Brain Fog Glossary
804 terms explained in plain language. Use this index to understand the clinical terminology used across causes, tests, and treatment explainers.
25-hydroxyvitamin D
The primary circulating form of vitamin D measured in blood tests (also called 25-OH vitamin D or calcidiol). Reflects total vitamin D from sun, food, and supplements over the past 2-3 weeks.
25-OH Vitamin D
Severe deficiency doubles dementia risk
4AT
A rapid bedside delirium screen used to flag acute confusion, inattention, and fluctuating mental status.
A1c + fasting glucose context review
This route is for the situation where HbA1c and fasting glucose do not fully explain a strong post-meal or fasting crash pattern.
AASP Sensory Profile
Adult sensory processing patterns
Ablation
Burning or destroying the surface of endometriosis lesions rather than removing them. Generally considered less effective than excision because deeper disease tissue may remain.
Acanthosis Nigricans
Dark, velvety patches on skin (neck, armpits, groin). A visible sign of insulin resistance. If you have this, your insulin is almost certainly elevated.
ACB
Now calculate the Anticholinergic Burden.
ACE Questionnaire
The ACE questionnaire counts types of childhood adversity: abuse, neglect, and household dysfunction before age 18.
ACE Score
Adverse Childhood Experiences score - a 10-question screening tool counting types of childhood adversity. Higher scores are associated with increased health risks including cognitive impairment.
acetylcholine
The primary neurotransmitter for memory, learning, and attention.
acetylcholinesterase
The enzyme that breaks down acetylcholine after nerve signal transmission. Organophosphate and carbamate pesticides inhibit this enzyme, causing acetylcholine to accumulate and overstimulate nerves. The mechanism behind pesticide-induced cognitive symptoms.
actigraphy
A wearable sleep-wake tracker used over days to weeks to show actual timing patterns when sleep logs and memory are unreliable.
Active B12 (Holotranscobalamin)
More accurate than serum B12 for cellular deficiency
Adaptogen
A plant-derived compound marketed as helping the body adapt to stress. Some adaptogens have small stress-response trials, but the category is not a diagnosis or a guarantee of endocrine benefit.
Adenomyosis
A condition where endometrial-like tissue grows into the muscular wall of the uterus. Frequently co-occurs with endometriosis and can cause heavy bleeding, painful periods, and cognitive symptoms through similar inflammatory pathways.
adenosine
A chemical that builds up during waking hours, creating sleep pressure. Caffeine works by blocking adenosine receptors; chronic use causes the brain to upregulate these receptors.
ADH and Osmolality
Antidiuretic hormone and blood concentration markers.
ADOS-2
Gold standard clinician-administered autism assessment using structured social scenarios.
Adrenal insufficiency
A medical disorder where the body does not produce enough cortisol. It can cause fatigue, dizziness, low blood pressure, and can become an emergency if severe.
AHI
Apnea-Hypopnea Index, a sleep-study metric used when sleep apnea is part of the ADHD differential.
Air Quality
The practical mix of ventilation, CO2, particulate matter, combustion byproducts, humidity, and chemical exposures in the air you spend time in.
Albuminuria / proteinuria
Protein leaking into the urine. This is a key marker of kidney damage and often shows up before severe symptoms do.
Alcohol
A central nervous system depressant that disrupts sleep architecture, depletes B vitamins (especially thiamine), and with regular use causes measurable hippocampal volume loss and neuroinflammation.
Alexithymia
Difficulty identifying and describing emotions. Present in ~50% of autistic adults. Makes brain fog harder to recognize and communicate.
Allopregnanolone
A neurosteroid metabolite of progesterone that modulates GABA-A receptors. In PMDD, the brain responds abnormally to allopregnanolone fluctuations, destabilizing the calming system.
Allostatic load
The cumulative physiological toll of chronic stress on the body, including effects on cortisol, immune function, metabolism, and cognitive performance.
alpha rhythm
Brain waves in the 8-13 Hz frequency range, associated with relaxed alertness, attention readiness, and cortical arousal regulation. Reduced posterior alpha is consistently found in brain fog patients across Long COVID, ME/CFS, and fibromyalgia studies (Babiloni 2024). Think of alpha as your brain's 'ready' signal - when it's low, you're not cognitively primed.
Alpha-wave intrusion
A sleep EEG finding where waking-type alpha waves intrude into deep sleep stages, preventing restorative sleep. Common in fibromyalgia and linked to next-day cognitive dysfunction and pain amplification.
AM Cortisol (8am)
Morning cortisol explainer focused on the timed 8am draw clinicians usually use for baseline adrenal-context questions.
AMH
Anti-Müllerian hormone - a hormone produced by ovarian follicles that reflects ovarian reserve. Elevated AMH is common in PCOS and correlates with follicle count. Used alongside other criteria to support PCOS diagnosis.
Amygdala
A threat-detection and emotion-processing region of the brain that becomes more reactive under stress.
amyloid
A protein that can accumulate in the brain when the glymphatic system isn't clearing waste effectively. Associated with Alzheimer's disease. Deep sleep is essential for amyloid clearance.
Amyloid-beta
A protein fragment involved in normal brain biology that can accumulate abnormally when clearance is impaired; it is often discussed in the context of Alzheimer disease and sleep-linked waste clearance.
ANA
Antinuclear Antibodies.
ANA (Antinuclear Antibodies)
Screening for autoimmune disease - positive in lupus, Sjögren's, RA
ANA (antinuclear antibody)
A blood test that detects antibodies directed against components of the cell nucleus. A positive ANA at 1:80 or above is the entry criterion for SLE classification per 2019 EULAR/ACR criteria. ANA results include titer (how concentrated the antibodies are) and pattern (homogeneous, speckled, nucleolar), both of which provide diagnostic clues.
anaerobic threshold
The activity intensity above which the body shifts into a less sustainable energy state. In ME/CFS and Long COVID, crossing it can contribute to post-exertional worsening.
anaphylaxis
A severe, potentially life-threatening allergic reaction involving multiple organ systems. Some MCAS patients experience anaphylaxis or anaphylactoid reactions. Epinephrine auto-injectors may be prescribed for patients with severe MCAS.
Androgen
A hormone in the testosterone family. In adults, androgens influence libido, muscle maintenance, recovery, body hair, and parts of motivation and cognitive drive.
Anemia
Anemia can contribute to brain fog.
Anhedonia
The inability to feel pleasure from activities that used to be enjoyable. A core depression symptom that helps distinguish it from fatigue-only conditions.
Anorexia Nervosa
An eating disorder characterized by restriction of energy intake leading to significantly low body weight, intense fear of weight gain, and distorted body image. Causes severe brain fog through glucose starvation, micronutrient depletion, and gray matter loss.
anosmia
Complete loss of sense of smell. Can be caused by nasal polyps, viral infection, or neurological conditions.
Anti-dsDNA Antibodies
Specific for systemic lupus erythematosus (SLE)
Anti-TNF Therapy
Biologic medications (infliximab, adalimumab) that block TNF-alpha. May directly improve brain fog by reducing TNF-alpha crossing the blood-brain barrier.
Anti-TPO
Antibodies against thyroid peroxidase, an enzyme involved in thyroid hormone production. Anti-TPO above 34 IU/mL is significant for Hashimoto's thyroiditis. Testing anti-TPO alongside TSH catches autoimmune thyroid disease that a normal TSH alone would miss.
Anticholinergic
A property of certain medications (including some antidepressants) that can worsen brain fog, memory, and concentration by blocking acetylcholine.
Anticholinergic burden
The cumulative cognitive-impairing effect of medications that block acetylcholine. Common culprits: antihistamines, sleep aids, certain antidepressants. Particularly relevant for women 40-60 who are often prescribed multiple medications.
Anticholinergic Burden Review
Anticholinergic medications block acetylcholine, one of the main neurotransmitters for attention and memory.
Anticholinergic Burden Score
A numerical estimate of total anticholinergic load from all current medications. A score of 3 or more is a meaningful clue that cognition may be taking a hit from the medication list.
Antiphospholipid antibodies
Autoantibodies associated with increased clotting risk and certain neuropsychiatric lupus manifestations. Testing includes anticardiolipin, anti-beta2-glycoprotein I, and lupus anticoagulant. Important for NPSLE risk stratification.
Anxiety
A high-alert state marked by worry, hypervigilance, panic physiology, or chronic threat-scanning that can crowd out concentration and memory.
apnea
Sleep apnea - repeated pauses in breathing during sleep that can cause heavy mornings and overlap with bedroom-air problems.
APOE-4
A genetic variant carried by ~25% of women. May modify the cognitive response to HRT - early evidence suggests APOE-4 carriers may benefit more from early-initiated hormone therapy.
AQ-10 Screening
Autism spectrum screening questionnaire
AQI
Air Quality Index - the public scale used to summarize outdoor air pollution risk. Higher AQI means dirtier air.
ARFID
Avoidant/Restrictive Food Intake Disorder. Significant food avoidance based on sensory sensitivity, fear of consequences, or low appetite - not body image. Can cause severe micronutrient deficiencies and brain fog without the weight/body concerns of anorexia.
ARIA
Amyloid-related imaging abnormalities. A side effect of anti-amyloid therapies (lecanemab, donanemab) involving brain swelling or microbleeds, monitored by regular MRI during treatment.
Aromatase
An enzyme that converts testosterone into estradiol. Aromatase activity tends to rise with higher body-fat levels, which can lower bioavailable testosterone.
ASL-MRI
Arterial Spin Labeling.
ASL-MRI (Arterial Spin Labeling)
Non-invasive brain blood flow measurement
ASMBS
American Society for Metabolic and Bariatric Surgery. Publishes the clinical practice guidelines for nutrition monitoring and supplementation after bariatric surgery.
ASRS-v1.1
The Adult ADHD Self-Report Scale, a short screening tool used to identify people who may need full ADHD evaluation.
ASRS-v1.1 (ADHD)
Patient-facing ADHD screener route matching the ASRS-v1.1 wording used in results cards and clinician conversations.
ASRS-v1.1 Screener
Adult ADHD Self-Report Scale - 6-question screener
Atomoxetine
A non-stimulant ADHD medication that works primarily through norepinephrine reuptake inhibition.
Attention fragmentation
A pattern of repeatedly broken focus caused by interruptions, notification anticipation, or rapid switching between digital inputs.
Attention Restoration Theory
A theory suggesting that natural environments restore directed attention because they engage the mind gently rather than demanding constant cognitive control.
aura
Neurological symptoms (visual disturbances, sensory changes, speech difficulty) occurring before or during the headache phase. Only about 25% of people with migraine experience aura.
Autism
A neurodevelopmental condition characterized by differences in social communication, sensory processing, and patterns of thinking. Brain fog in autistic adults typically stems from autistic burnout.
Autistic burnout
Chronic exhaustion, skill regression, and reduced tolerance from sustained masking and sensory overload. First formally defined by Raymaker et al. in 2020. Distinct from occupational burnout and depression.
Autoimmune
Autoimmune is a nearby overlapping cause that's often worth ruling out when the story pattern is similar.
Autoimmune disease
A category of conditions where the immune system attacks the body's own tissues. Common examples include Hashimoto's thyroiditis, systemic lupus erythematosus, rheumatoid arthritis, celiac disease, and Sjogren's syndrome. Brain fog is a frequent but under-recognized symptom across most autoimmune conditions.
Autoimmune encephalitis
A treatable immune attack on the brain that can initially look psychiatric, especially when the onset is sudden and the behavior change is dramatic.
autophagy
The cell's self-cleaning process - damaged components are broken down and recycled. Triggered by fasting, exercise, and sleep. Impaired autophagy leads to cellular debris accumulation and cognitive decline.
B12
Holotranscobalamin.
B2 (Riboflavin)
A B-vitamin involved in mitochondrial energy production. 400mg/day has AHS Grade B evidence for migraine prevention. Not to be confused with magnesium, which is a separate supplement also used for migraine.
Bartonella
A genus of gram-negative bacteria transmitted primarily through cat scratches and flea bites that can cause chronic infection with neuropsychiatric, dermatologic, and vascular symptoms including brain fog, rage, anxiety, shin streaks, and small fiber neuropathy.
Bartonella IgG/IgM
Bartonella infection screening
Bartonella PCR
Direct detection of Bartonella DNA
Baseline Cognitive Assessment
A baseline screen helps document that the problem is measurable, track change over time, and decide when formal neuropsychology is worth the extra effort.
Basic Metabolic Panel
Blood test measuring sodium, potassium, chloride, bicarbonate, glucose, BUN, and creatinine. First-line screening for electrolyte imbalance and kidney function.
BBB
Blood-brain barrier - the selective membrane protecting the brain from harmful substances in the bloodstream. Damage to the BBB is a key driver of brain fog.
BDNF
Brain-derived neurotrophic factor - a protein that promotes neuron growth, survival, and new connections.
Beers Criteria
A medication-safety framework from the American Geriatrics Society listing drugs that are potentially inappropriate or higher-risk for older adults, including many that affect cognition.
Behavioral activation
A depression treatment approach where you schedule activities before feeling motivated - action precedes motivation. As effective as CBT for depression.
Beighton Score
Joint hypermobility assessment for EDS/HSD
benzodiazepine
A class of sedative medications (Valium, Xanax, Ativan) that enhance GABA activity. Effective short-term for anxiety but cause cognitive impairment, memory problems, and dependence with regular use.
Bergen Social Media Addiction Scale
A short questionnaire used to screen for problematic social-media use by asking about salience, tolerance, withdrawal, conflict, relapse, and mood modification.
beta-hydroxybutyrate
The primary ketone body used by the brain during nutritional ketosis. Produced in the liver from fatty acids, it crosses the blood-brain barrier and serves as an alternative fuel to glucose.
Bile acid sequestrant
A drug class that binds bile acids in the gut. Examples include cholestyramine and colesevelam; some mold-focused clinicians use them as binders.
bioaccumulation
Process by which mercury concentration increases up the food chain.
Biofilm
A protective matrix that bacteria create around themselves, making them harder for antibiotics and the immune system to reach. Bartonella can form biofilms, which may contribute to treatment resistance and relapse.
Biologic
Medications made from living cells targeting specific immune pathways. In IBD: anti-TNF, anti-integrin (vedolizumab), anti-IL-12/23 (ustekinumab). More targeted than traditional immunosuppressants.
biomarker
A measurable substance in the body that indicates a biological state or condition. Blood biomarkers like ferritin, hs-CRP, and TSH help identify the root cause of brain fog objectively.
biopsychosocial model
A framework viewing health as the product of biological, psychological, and social factors interacting - not just physical disease.
Blood Mercury
Mercury exposure marker that reflects recent-to-intermediate methylmercury exposure over roughly the past 2-3 months.
blood mercury level
Measurement of mercury in whole blood.
blood pooling
In POTS and dysautonomia, blood accumulates in the lower body when standing due to poor venous return. Causes reduced cerebral perfusion and brain fog. Visible as purple/red discoloration in feet (acrocyanosis). Treated with compression garments and counter-maneuvers.
Blood Sugar Assessment
This bundle is more useful than a single glucose marker when the story suggests post-meal crashes, normal average labs with variability, or early insulin resistance.
blood-brain barrier
A selective membrane that helps control what reaches the brain from the bloodstream.
Blue light
Short-wavelength visible light from screens and LEDs that can shift circadian timing when exposure is concentrated late in the evening.
Bortezomib (Velcade)
A proteasome inhibitor used in myeloma treatment. Effective against myeloma cells but causes peripheral neuropathy in 30-40% of patients.
Box breathing
A structured breathing pattern with equal-length inhale, hold, exhale, and hold phases, often used to reduce physiological arousal.
BPD/DS (Biliopancreatic Diversion with Duodenal Switch)
The most malabsorptive bariatric procedure. Bypasses the majority of the small intestine, causing the highest rates of nutrient deficiency.
Brain MRI
Structural neuroimaging used to evaluate red flags and differential neurological causes.
Brain rot
An emerging informal term for the dulled, low-depth mental state linked to compulsive low-quality digital content consumption. It isn't a formal medical diagnosis.
Breath test
The primary diagnostic test for SIBO. You drink a sugar solution (lactulose or glucose) and breathe into collection tubes over 2-3 hours. Elevated hydrogen, methane, or hydrogen sulfide indicates bacterial overgrowth.
BRIEF-A
Behavior Rating Inventory of Executive Function
Bristol Stool Chart
A clinical scale classifying stool into 7 types based on form. Types 3-4 are considered ideal; types 1-2 indicate constipation; types 6-7 indicate diarrhea.
Buffalo Protocol
The Buffalo Concussion Treadmill Test - a graded aerobic exercise protocol that identifies your symptom-free heart rate threshold. Exercise at 80-90% of this threshold to accelerate recovery.
Bulimia Nervosa
An eating disorder characterized by cycles of binge eating followed by compensatory behaviors (purging, fasting, excessive exercise). Causes acute brain fog through electrolyte derangements, especially potassium and magnesium depletion.
BUN
Blood urea nitrogen - another waste marker that rises with dehydration and kidney dysfunction.
Burnout
A state of chronic overload and depleted mental reserve classified by the WHO (ICD-11 QD85) as an occupational phenomenon - not a medical condition - resulting from chronic workplace stress that hasn't been successfully managed.
Burnout Assessment Tool (BAT)
A newer burnout instrument (2020) that explicitly measures cognitive impairment as one of four core dimensions alongside exhaustion, mental distance, and emotional impairment.
butyrate
A short-chain fatty acid produced when gut bacteria ferment dietary fibre. Strengthens the gut lining, reduces inflammation, and crosses the blood-brain barrier to directly support neurons.
C-PTSD
Complex PTSD. Recognized by the ICD-11 as a distinct diagnosis caused by repeated or prolonged trauma. Includes core PTSD symptoms plus emotional dysregulation, negative self-concept, and relationship disturbance.
C-Reactive Protein
General inflammation marker - less sensitive than hs-CRP
C4a (Complement)
Part of the complement immune cascade.
CA-125
A blood test sometimes elevated in endometriosis but not specific or sensitive enough for diagnosis. Normal CA-125 doesn't rule out endometriosis. Not recommended as a standalone diagnostic test.
Caffeine
A stimulant that blocks adenosine receptors, temporarily improving alertness but causing jitters, crashes, withdrawal fog, and sleep disruption with chronic use.
calcitriol
The active hormonal form of vitamin D (1,25-dihydroxyvitamin D). Produced mainly in the kidneys. Can be normal even when deficient, so it isn't the right screening test.
calprotectin
A stool marker of intestinal inflammation. Levels below 50 mcg/g help rule out inflammatory bowel disease; elevated levels warrant further investigation.
CAM
Confusion Assessment Method. A structured tool used to diagnose delirium in clinical settings.
Candida Antibody Panel (IgG, IgA, IgM)
Blood test measuring immune response to Candida.
CAPS-5
Clinician-Administered PTSD Scale for DSM-5. The gold-standard structured interview for diagnosing and measuring PTSD severity. Requires trained administration. Uses frequency and intensity ratings with a diagnostic algorithm.
Carbon monoxide
A colorless, odorless gas that can impair thinking, trigger headaches, and become dangerous or life-threatening with ongoing exposure.
Cast nephropathy
Kidney damage caused by myeloma light chains forming casts in the kidney tubules. The most common cause of myeloma-related kidney failure.
CBC
Complete blood count - a basic blood panel that measures red cells, white cells, and platelets.
CBC + CMP
Baseline panel combining complete blood count and metabolic chemistry for broad screening context.
CBC with Differential
Core blood count panel used to review white cell patterns, hemoglobin, and platelet context.
CBT
Cognitive behavioral therapy, a structured psychological treatment that can help when problematic internet or social media use becomes compulsive.
CBT for ADHD
A structured, skills-based cognitive behavioral approach adapted for executive dysfunction rather than generic talk therapy.
CBT-I
Cognitive Behavioral Therapy for Insomnia. Well-evidenced for menopausal insomnia with improvements persisting 6+ months. Since sleep disruption drives much of menopause fog, this is a high-value intervention.
CCI
Craniocervical instability.
CDT
Carbohydrate-Deficient Transferrin.
CDT (Carbohydrate-Deficient Transferrin)
Specific marker for chronic alcohol consumption
Celiac
An autoimmune reaction to gluten that damages the small intestine and can cause digestive symptoms, nutrient deficiency, inflammation, and brain fog. Some people experience the cognitive part as prominently as the gut part - up to 10-22% of cases present with neurological symptoms only.
Central Sensitisation Inventory
Screens for central sensitization syndromes
Central sensitization
A state where the central nervous system amplifies pain signals and sensory input. In fibromyalgia, this amplification affects cognition as well as pain - the same mechanism that makes light touch painful also overwhelms thinking capacity.
Central Sensitization Inventory (CSI)
A 25-item validated self-report questionnaire that screens for central sensitization. Scores above 40 suggest central sensitization is likely. Used in pain clinics worldwide.
Cerebral blood flow
The volume of blood flowing through brain tissue per unit time. Prolonged sitting reduces cerebral blood flow across the day, while brief movement breaks restore it. Morning exercise has been shown to protect brain blood flow throughout the afternoon.
cerebral hypoperfusion
Reduced blood flow to the brain. In POTS, this occurs on standing when blood pools in the legs instead of reaching the brain. Directly causes brain fog, difficulty concentrating, and cognitive slowing. Measured via transcranial Doppler ultrasound.
Cervical
Cervical can contribute to brain fog.
cervicogenic
Originating from the cervical spine (neck). Cervicogenic headache and dizziness can mimic or coexist with post-concussion symptoms and are treatable with physiotherapy.
CGM
Continuous glucose monitor - a wearable device that tracks blood sugar every few minutes, revealing patterns that finger-stick tests miss. A 2-week CGM trial can show exactly which foods, activities, and timing patterns affect your glucose and cognition.
CGM (Continuous Glucose Monitor)
14-day glucose variability tracking - reveals hidden spikes
CGRP
Calcitonin gene-related peptide - the key neuropeptide in migraine pathophysiology. CGRP-blocking medications (erenumab, fremanezumab, galcanezumab) are the first migraine-specific preventive treatments.
chelation therapy
Medical treatment using drugs (DMSA, DMPS, or EDTA) that bind heavy metals in the blood for excretion.
Chemobrain
Chemobrain can contribute to brain fog.
cholecalciferol
Vitamin D3, the form produced by skin in response to UVB sunlight and the preferred supplementation form. More effective than ergocalciferol (D2) at raising blood levels.
Cholestyramine
A bile-acid sequestrant prescription drug used as a binder in some CIRS-style treatment plans after exposure control.
Cholinesterase inhibitors
Medications (donepezil, rivastigmine, galantamine) that increase acetylcholine levels in the brain, used to manage symptoms of Alzheimer's disease and other dementias.
chronicity
The tendency of a condition to persist over time. In post-viral illness, chronicity means symptoms can last for months rather than days or weeks and usually require active management rather than passive waiting.
Cinacalcet
A calcimimetic drug that lowers calcium and PTH levels by making the parathyroid glands more sensitive to calcium. Used when surgery isn't possible. Not a cure - calcium rises if the drug is stopped.
circadian
Relating to the body's ~24-hour internal clock. Circadian disruption (irregular sleep times, night-shift work, blue light at night) impairs melatonin production, cortisol rhythm, and cognitive performance.
Circadian anchoring
Using a consistent wake time and morning light exposure to stabilize the body clock so melatonin timing and alertness become more predictable.
circadian drift
A repeating pattern where sleep time keeps sliding later or becomes irregular enough that the brain never gets a stable wake cue.
Circadian rhythm
The body’s internal 24-hour timing system that affects alertness, sleep, hormone timing, and next-day cognitive function.
CIRS
Chronic Inflammatory Response Syndrome - a proposed condition where biotoxins (from mold, Lyme, etc.) trigger persistent innate immune activation. Characterized by multiple symptoms including brain fog, fatigue, and sensitivity to environments. Controversial; not recognized in mainstream guidelines.
CKD
Chronic kidney disease - long-term loss of kidney function that can affect cognition through toxin buildup, anemia, blood-pressure instability, and metabolic stress.
Co-infection Panel
Tests for Babesia, Bartonella, Anaplasma, Ehrlichia
CO₂
Carbon dioxide. Indoors, rising CO2 is mainly a ventilation marker: when it climbs, clear thinking often falls.
CO₂ Monitor
High CO₂ = poor ventilation = cognitive impairment
CO₂ Monitoring
CO2 is mainly a ventilation marker, but it is one of the fastest ways to test whether your room is part of the brain-fog story.
Cognitive impairment (burnout dimension)
The fourth dimension of burnout as defined by the BAT (2020). Includes memory lapses, difficulty concentrating, inability to think clearly, and making mistakes. Validated as a core feature of burnout, not a side effect.
Cognitive Processing Therapy
A 12-session structured psychotherapy for PTSD that focuses on identifying and challenging unhelpful trauma-related beliefs. APA and VA/DoD recommended first-line alongside PE and EMDR.
Cognitive remediation
Computerized training programs targeting attention, memory, and executive function. An emerging approach for persistent cognitive symptoms after depression treatment.
Cognitive reserve
The brain’s resilience against injury, aging, or disease. Higher reserve means a person may function better for longer despite the same biological stressor.
Colesevelam
A bile-acid sequestrant prescription medication used mainly for cholesterol and diabetes care. Some CIRS clinicians use it as a gentler alternative to cholestyramine.
Collateral history
Information from a parent, partner, sibling, report card, or older records that helps establish the childhood pattern.
Comorbidity
The presence of two or more conditions at the same time. Burnout commonly co-occurs with depression, anxiety, sleep disorders, and thyroid dysfunction. Managing comorbid conditions is essential for recovery.
Complex PTSD
Recognised by the ICD-11 as a distinct diagnosis caused by repeated or prolonged trauma (childhood abuse, domestic violence, captivity). Includes core PTSD symptoms plus emotional dysregulation, negative self-concept, and relationship disturbance. Recovery may require a phase-based treatment approach.
Complex PTSD (cPTSD)
A condition resulting from prolonged or repeated trauma, especially in childhood. Includes PTSD symptoms plus difficulties with emotion regulation, self-concept, and relationships. Recognized in ICD-11 but not yet in DSM-5.
Comprehensive Nutrient Panel
This bundle is useful when the story sounds like low reserve, blood loss, restrictive intake, malabsorption, or medication-related depletion and you want one coherent nutrient conversation instead of scattered one-off r…
convergence insufficiency
Difficulty bringing both eyes inward to focus on a near object. Common after concussion and treatable with vision therapy.
Copper Myelopathy
Spinal cord damage from copper deficiency. Mimics B12 deficiency on labs (both cause macrocytic anemia) but causes irreversible neurological damage. Only 5.1% recover to baseline.
cortical spreading depression
A wave of electrical and chemical activity that spreads slowly across the brain surface at about 3mm per minute, temporarily silencing neural activity. The mechanism behind migraine aura.
Cortisol
The body's main glucocorticoid stress hormone. It follows a daily rhythm and helps regulate alertness, glucose availability, blood pressure, and stress responses.
cortisol awakening response
The normal rise in cortisol during the first 30 to 45 minutes after waking. A blunted pattern can show up in chronic stress and poor recovery states.
cotinine
A metabolite of nicotine with a half-life of about 16-19 hours, used in urine or blood tests to confirm recent tobacco or nicotine use or abstinence.
counter-maneuvers
Physical movements to increase blood return to the heart in POTS and orthostatic intolerance. Examples: leg crossing with thigh tensing, squatting, toe raises, fist clenching. Used before and during standing to prevent symptoms.
CPAP
Continuous Positive Airway Pressure - the gold-standard treatment for obstructive sleep apnea.
CPET
Cardiopulmonary exercise test - measures oxygen consumption, carbon dioxide output, heart rate, and ventilation during exercise. A two-day CPET protocol can objectively demonstrate post-exertional malaise in ME/CFS by showing reduced capacity on day 2. Gold standard for documenting exercise intolerance.
CRAB criteria
The four defining features of symptomatic myeloma: Calcium elevation, Renal impairment, Anemia, and Bone lesions.
Creatinine
A waste product filtered by the kidneys and used to calculate eGFR. It's useful, but not enough on its own.
Crohn's Disease
A type of IBD that can affect any part of the GI tract. Commonly affects the ileum (where B12 is absorbed), making B12 deficiency and brain fog particularly common.
cromolyn
Cromolyn sodium (Gastrocrom) - a mast cell stabilizer taken before meals to prevent GI-triggered mast cell degranulation. Prescription medication used as second-line treatment in MCAS.
CSI (Central Sensitization Inventory)
A free 25-question screening tool for central sensitization. A score of 40 or above indicates the nervous system is amplifying pain signals. Developed by Mayer et al. (2012), with the clinical cutoff established by Neblett et al. (2013).
CTE
Chronic traumatic encephalopathy - a neurodegenerative condition associated with repetitive head impacts over years. Currently diagnosable only post-mortem. Distinct from PCS but shares risk factors (repeated concussions).
Cushing's syndrome
A medical disorder caused by pathologically high cortisol exposure. It requires clinician-guided diagnosis and should not be confused with everyday stress.
cyclic sighing
A structured breathing technique using a double inhale and long exhale. It has trial support for improving mood and reducing anxiety.
CYP1A2
The liver enzyme responsible for metabolizing about 95% of caffeine. Genetic variants create fast and slow metabolizers with very different caffeine sensitivity and half-life.
Cystatin C
Alternative kidney filtration marker used when creatinine may be misleading or when you need a cleaner confirmatory estimate of kidney function.
cytokine
Chemical messengers released by immune cells. Pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) drive brain fog by disrupting neuron communication. Anti-inflammatory cytokines help resolve it.
D-Arabinitol (Urine)
Fungal metabolite marker specific to Candida species.
D-dimer
Clotting marker - elevated in Long COVID microclots
D-lactic acidosis
A metabolic condition where D-lactate-producing bacteria in the gut cause neurological symptoms including brain fog, confusion, and slurred speech. Linked to SIBO and probiotic overuse.
DAO
Diamine oxidase - the enzyme that breaks down histamine in the gut. Produced primarily in intestinal enterocytes. Requires vitamin B6, copper, and vitamin C as cofactors.
DAO (Diamine Oxidase) Levels
Low DAO = impaired histamine breakdown = histamine intolerance
deconditioning
A state of reduced physical fitness from prolonged inactivity that worsens orthostatic intolerance and POTS symptoms.
Deep infiltrating endometriosis
Endometriosis lesions that penetrate more than 5mm below the peritoneal surface. Can affect bowel, bladder, and other organs. Often requires specialist surgical expertise for adequate treatment.
Default mode network
A brain network active during rest, mind-wandering, and self-referential thought. Loneliness is associated with altered default mode network connectivity, potentially reflecting an internally-focused cognitive orientation that impairs outward engagement.
degranulation
The process by which mast cells release their stored inflammatory mediators (histamine, tryptase, prostaglandins, cytokines) into surrounding tissue. In MCAS, degranulation occurs inappropriately in response to normally harmless triggers.
delirium
An acute, fluctuating problem with attention and awareness. After surgery, it should be treated as a medical problem, not brushed off as normal recovery.
dendritic
Relating to dendrites - the branch-like extensions of neurons that receive signals from other neurons. Dendritic sprouting (growth of new branches) is a sign of healthy neuroplasticity.
DePaul Symptom Questionnaire
A validated symptom questionnaire used in ME/CFS research and clinical workups to capture PEM, sleep, pain, autonomic, and cognitive patterns in a structured way.
depersonalization
A dissociative experience where you feel detached from yourself, your body, or your usual sense of identity.
deprescribing
A clinician-guided process of tapering, stopping, or replacing medications that may be causing more harm than benefit.
Depression
A mood disorder whose symptoms (cognitive dysfunction, fatigue, mood changes) overlap significantly with chronic Bartonella infection. Many patients with Bartonella-driven neuropsychiatric symptoms are initially misdiagnosed with depression.
derealization
A dissociative experience where the external world feels unreal, flat, dreamlike, or strangely distant.
dermatographia
Skin writing - a condition where light scratching causes raised red marks that persist for minutes. Indicates mast cell hyperreactivity and may be a visible sign of histamine sensitivity.
Dexamethasone
A high-dose corticosteroid used in almost every myeloma regimen. Causes insomnia, mood swings, and cognitive disruption. Given in cycles.
Dexamethasone suppression test
A cortisol test where a small dose of dexamethasone is taken the night before blood work to check whether cortisol production suppresses normally.
DHEA-S
A long-acting adrenal hormone often used alongside cortisol to add context to chronic stress and HPA-axis discussions.
Diabetes
A metabolic condition in which the body can't properly regulate blood glucose, either because the pancreas produces insufficient insulin (Type 1) or because cells become resistant to insulin's effects (Type 2). Both types can impair cognition through glucose instability, neuroinflammation, and microvascular damage.
DIAGNOSTIC
THE COLLAR TEST.
Dialysis
A treatment that removes waste products and excess fluid from the blood when the kidneys can no longer do so adequately.
Diamine oxidase
DAO. The main enzyme responsible for breaking down ingested histamine in the gut. Low DAO activity leads to histamine intolerance, where aged, fermented, and leftover foods trigger symptoms including brain fog, flushing, headache, and GI distress. DAO levels can be measured by blood test.
Dienogest
A progestin medication with strong evidence for endometriosis symptom control. Taken as a daily 2mg oral tablet. Generally better tolerated than GnRH agonists with fewer cognitive side effects.
Digital Motion X-ray
Real-time imaging of cervical instability
DII
Dietary Inflammatory Index - a literature-derived scoring system that rates the inflammatory potential of a diet based on 30+ nutrients. Higher DII = more pro-inflammatory. UK Biobank data links higher DII scores to increased risk of anxiety, depression, sleep disorders, and dementia through measurable blood markers.
Disease-modifying therapy (DMARD)
Medications that target the underlying autoimmune process rather than just managing symptoms. Examples include hydroxychloroquine for lupus, methotrexate for RA, and levothyroxine for Hashimoto's. Early treatment often improves cognitive symptoms alongside other disease markers.
dissociation
A stress-linked disconnection between attention, emotion, body sensation, or surroundings. It can happen in anxiety without meaning psychosis.
DIVA-5
A structured diagnostic interview used in some adult ADHD assessments.
dive reflex
A hardwired mammalian reflex triggered by cold water on the face that can slow heart rate and help interrupt panic physiology.
DMSA / DMPS
Chelating medicines used in confirmed heavy-metal poisoning under medical supervision. They aren't routine treatment for mild dietary mercury concerns.
Donanemab
An anti-amyloid antibody for early Alzheimer's disease. The TRAILBLAZER-ALZ 2 trial showed 35% slowing of decline, with nearly half of treated patients showing no decline at one year.
Doomscrolling
Compulsive, repetitive consumption of distressing or low-value content that keeps attention captured without restoring clarity.
Dopamine
A neurotransmitter involved in reward, motivation, and attention regulation. ADHD treatment often targets dopamine and norepinephrine pathways.
drift diffusion model
A computational model describing how the brain accumulates information when making decisions. In Long COVID, reduced drift rate and altered decision boundaries show slowed information processing and need for more evidence before deciding.
DRSP
Daily Record of Severity of Problems - a validated daily symptom tracking tool for diagnosing PMDD. Requires tracking for at least two menstrual cycles to confirm the pattern of luteal-phase symptoms with follicular-phase relief.
drug-drug interaction
A situation where two or more medications change how one another work, increasing the chance of side effects or changing how strongly the drugs affect the brain.
DSM-5
The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, which lays out current ADHD diagnostic criteria.
DTI
Diffusion tensor imaging - advanced MRI technique that can reveal white matter changes not visible on standard MRI scans.
DTI MRI (Diffusion Tensor Imaging)
Advanced brain imaging - detects concussion damage
Dual N-Back
A working-memory training task where you track visual and auditory stimuli across multiple steps back in time. It is one of the few brain-training tasks with some transfer-effect evidence.
Dumping Syndrome
Rapid movement of food from the stomach pouch into the small intestine, causing nausea, cramping, diarrhea, and blood sugar swings. Early dumping (within 30 min) and late dumping (1-3 hours) have different mechanisms.
DUTCH test
A specialty dried urine hormone test that estimates cortisol patterns and sex-hormone metabolites over a day. It is not a standard first-line medical test.
dysautonomia
Dysfunction of the autonomic nervous system - the automatic controller of heart rate, blood pressure, digestion, and temperature.
dysbiosis
An imbalance in gut bacteria - too many inflammatory species, too few protective ones. Drives systemic inflammation, impairs nutrient absorption, and disrupts neurotransmitter production.
Dysmenorrhea
Painful menstrual periods. Primary dysmenorrhea has no underlying cause. Secondary dysmenorrhea (caused by conditions like endometriosis) typically worsens over time and may not respond to standard painkillers.
EA
Early Antigen - the key EBV reactivation marker. Elevated EA with positive VCA IgG and negative VCA IgM suggests the virus is actively replicating.
EAET
Emotional Awareness and Expression Therapy - a structured psychotherapy that targets emotional processing pathways involved in chronic pain amplification. Has evidence for fibromyalgia, outperforming CBT in a 2017 trial.
EAET (Emotional Awareness and Expression Therapy)
A psychological treatment for chronic pain that addresses emotional components of pain processing. A 2024 RCT found EAET produced clinically significant pain reduction in 35% of participants vs 7% with CBT (Yarns et al., JAMA Netw Open).
EBNA
Epstein-Barr Nuclear Antigen - develops 2-4 months after infection. Helps date the infection: negative EBNA with positive VCA IgG suggests relatively recent infection.
EBNA IgG (Epstein-Barr Nuclear Antigen)
Indicates past infection with a timing clue: EBNA typically develops 2-4 months after acute infection.
EBV
Epstein-Barr virus - a herpesvirus carried by about 90% of adults. It causes infectious mononucleosis and can reactivate to cause brain fog and fatigue.
EBV Early Antigen (EA-D IgG)
The key marker for EBV reactivation.
EBV Reactivation Panel
Most doctors only order VCA IgG, which is positive in 90% of adults and tells you nothing about current viral activity.
EBV VCA IgG (Viral Capsid Antigen IgG)
Shows past EBV exposure.
EBV VCA IgM (Viral Capsid Antigen IgM)
Indicates recent or acute EBV infection within the past 4-6 weeks.
EDS
Ehlers-Danlos Syndrome.
eGFR
Estimated glomerular filtration rate - a calculated measure of how well the kidneys are filtering blood. The trend is usually more useful than a single result.
Electrolytes
Minerals (sodium, potassium, magnesium, calcium) that carry electrical charges and are essential for nerve signaling, muscle function, and brain activity. Imbalance can cause brain fog, confusion, muscle cramps, and fatigue.
elimination diet
A structured approach to identifying food triggers: remove suspected foods for 2–4 weeks, then reintroduce one at a time while monitoring symptoms. The gold standard for finding diet-driven brain fog.
Elimination-reintroduction diet
The gold standard for identifying food sensitivities. Phase 1: remove suspected trigger foods for 2-4 weeks. Phase 2: systematically reintroduce one food every 3-4 days while tracking symptoms. Clear reactions during reintroduction confirm that food as a trigger.
ELISA (Lyme)
Lyme screening - high false negative rate
EMDR
Eye Movement Desensitization and Reprocessing - a trauma therapy using bilateral stimulation to process traumatic memories. NICE-recommended first-line treatment for PTSD.
EMF
Electromagnetic fields generated by electrical devices and wireless systems. Brain-fog relevance remains controversial and low-priority compared with better-supported triggers.
Emotional exhaustion
The feeling of being emotionally drained and depleted. The first and most prominent dimension of burnout in the Maslach model. Often described as having nothing left to give.
Emotional Flashback
A sudden regression to the emotional state of a past trauma without a visual memory. The person feels the fear, helplessness, or shame of the original event without knowing why. Common in developmental trauma.
EncephalApp
A Stroop-style app used to help screen for covert hepatic encephalopathy.
Endometriosis
A chronic inflammatory condition where tissue similar to the uterine lining grows outside the uterus. Affects up to 1 in 10 women of reproductive age. The resulting pain, inflammation, and hormonal disruption can impair concentration, memory, and processing speed.
energy envelope
A pacing concept in ME/CFS where you plan daily activity to stay within the amount of energy your body can reliably tolerate without triggering a crash.
enterochromaffin cells
Specialized cells in the gut lining that produce most of the body serotonin and act as sensors connecting gut contents to the nervous system.
Enterogenic Dementia
Emerging concept describing cognitive decline from chronic gut inflammation. IBD patients show 17% higher dementia risk with onset 7+ years earlier.
Environmental Air Quality Review
Air-quality brain fog is usually diagnosed by pattern and exposure context rather than by bloodwork.
ePCR
Enrichment PCR - a specialized, more sensitive form of PCR testing that first enriches the blood sample to increase bacterial DNA concentration before amplification. Available through specialized reference laboratories for Bartonella detection when standard serology is negative.
EPDS
Edinburgh Postnatal Depression Scale - a validated 10-question screening tool for postnatal depression. Score above 13 suggests probable depression. Developed by Cox et al. in 1987 and used globally.
EPOS
European Position Paper on Rhinosinusitis - the most comprehensive evidence-based guideline for CRS diagnosis and management. Current version: EPOS 2020.
Epworth
Epworth Sleepiness Scale - an 8-question self-assessment measuring daytime sleepiness. Score your likelihood of dozing in different situations (reading, watching TV, as a passenger). Score ≥10 = excessive daytime sleepiness, suggesting a sleep disorder.
Epworth Sleepiness Scale
A short questionnaire that estimates how likely you're to fall asleep in ordinary situations; high scores suggest daytime sleepiness is real, not imagined.
Equol
Active metabolite of soy isoflavones produced by specific gut bacteria. Only 30-50% of Western populations produce equol, which may explain variable cognitive response to soy/phytoestrogen supplements.
ergocalciferol
Vitamin D2, a plant-derived form of vitamin D. Less effective than D3 (cholecalciferol) at raising and maintaining blood levels. Often prescribed in high-dose form.
ERMI
Environmental Relative Moldiness Index. An EPA-developed dust-DNA metric that estimates mold burden in a building. Originally for research, not clinical use. A low ERMI does not rule out mold in walls; a high ERMI does not prove symptoms are mold-caused.
ERMI (Environmental Relative Moldiness Index)
Home mold DNA test - identifies problematic species
ESR
Erythrocyte Sedimentation Rate.
ESR (Erythrocyte Sedimentation Rate)
Non-specific inflammation marker - elevated in autoimmune conditions
Estradiol
The primary form of estrogen. Regulates brain glucose metabolism, supports dopamine function, and maintains neuronal health. Transdermal delivery (patches/gel) is preferred over oral for cognitive outcomes.
Estrobolome
The collection of gut bacteria that regulate circulating estrogen levels. Menopause reduces gut microbial diversity, which may further reduce circulating estrogen - creating a vicious cycle.
Excision surgery
Surgical removal of endometriosis lesions by cutting them out completely, as opposed to ablation (burning the surface). Excision by a specialist has better outcomes and lower recurrence rates than ablation.
Executive dysfunction
Difficulty organizing, initiating, sequencing, and following through, even when the task is understood.
Executive function
The brain's project manager - handles working memory, cognitive flexibility, and task initiation. Differences worsen dramatically during burnout.
Expressive writing
A structured writing exercise where you write openly about a stressful experience for a short, fixed block of time.
Familial hypocalciuric hypercalcemia (FHH)
A benign genetic condition that causes mildly elevated calcium and can mimic PHPT. Distinguished by low 24-hour urine calcium. Important to rule out before surgery because FHH doesn't require treatment.
Fasting Glucose
Higher fasting glucose impairs executive function
Fasting Insulin
A blood test measuring insulin levels after an overnight fast. High fasting insulin with normal fasting glucose indicates insulin resistance, which can be present years before glucose rises. Not part of standard screening but clinically useful for identifying early metabolic dysfunction.
Fatigue
Fatigue is a nearby overlapping cause that is often worth ruling out when the story pattern is similar.
feature importance
In machine learning, a score indicating how much a variable contributes to predicting an outcome. Higher feature importance means the model relied more heavily on that variable when separating groups or making predictions.
Fecal Calprotectin
A stool test measuring gut inflammation. Below 50 mcg/g rules out significant inflammation. Above 200 suggests active IBD. More specific to gut inflammation than CRP.
Ferritin
A blood marker reflecting iron stores. Low ferritin can worsen fatigue, restless legs, and in some cases attention symptoms.
FESS
Functional endoscopic sinus surgery - minimally invasive surgery to open blocked sinus drainage pathways.
FIB-4
A non-invasive liver-fibrosis estimate derived from age, AST, ALT, and platelet count.
Fibro fog
The cognitive dysfunction associated with fibromyalgia, characterized by difficulty with word-finding, working memory, processing speed, and concentration. Often rated by patients as more disabling than the pain itself.
Fibromyalgia
A chronic pain and central-sensitization condition that affects sleep, sensory tolerance, fatigue, and cognition. Fibro fog commonly reflects the combined burden of pain, poor sleep, and nervous-system overload.
Finger Tapping Test
Simple motor-speed screening task sometimes used in cognitive and neurological assessments.
FIQR
Fibromyalgia Impact Questionnaire Revised - a validated self-report instrument measuring the overall impact of fibromyalgia on daily functioning, including physical impairment, overall impact, and symptom severity.
Flashback
A trauma-related intrusion where the person re-experiences a past event as if it were happening now, often with vivid sensory and emotional components. A hallmark symptom of PTSD distinct from ordinary memory recall.
Flexion-Extension Imaging
Dynamic X-ray for cervical spine movement
fludrocortisone
A mineralocorticoid medication that helps the body retain sodium and water, increasing blood volume. Used in POTS and orthostatic hypotension to improve cerebral perfusion.
FODMAP
Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols - short-chain carbohydrates that are poorly absorbed and rapidly fermented by gut bacteria. A landmark 2013 trial found that FODMAPs, not gluten, may be the actual trigger in many people who believe they're gluten-sensitive.
folate
Vitamin B9 - essential for methylation, DNA repair, and neurotransmitter production.
Folate (Serum or RBC)
Essential for methylation and neurotransmitter synthesis
follicular phase
The first half of the menstrual cycle, from menstruation to ovulation (roughly days 1-14). Estrogen rises during this phase. In PMDD, symptoms are absent or minimal during the follicular phase - this contrast is diagnostic.
FoMO
Fear of missing out. In digital-overload contexts it can make silence, batching, and distance from the phone feel harder than they should.
Food sensitivity
A repeatable adverse reaction to specific foods that doesn't involve IgE-mediated allergy. Unlike true allergies (immediate, potentially severe), food sensitivities cause delayed reactions (24-72 hours) including brain fog, GI symptoms, headache, and fatigue. Identified through systematic elimination-reintroduction, not commercial IgG tests.
Free T3
The active form of thyroid hormone that directly affects brain metabolism.
Free T4
The storage form of thyroid hormone.
Free Testosterone
The bioactive form of testosterone not bound to proteins. More sensitive than total testosterone for detecting hyperandrogenism in PCOS.
Freeze Response
A survival response where the nervous system immobilizes the body when fight or flight isn't possible. Experienced as feeling stuck, blank, unable to think or move. A major contributor to trauma fog.
Frontotemporal dementia
A group of brain disorders caused by degeneration of the frontal and temporal lobes. Often presents with personality changes, loss of empathy, impulsivity, or language difficulties rather than memory loss. Most common young-onset dementia.
FSH
Follicle-Stimulating Hormone. Rises when ovarian function declines. Unreliable single measurement during perimenopause because levels fluctuate dramatically. Diagnosis is clinical, not lab-based.
FSH (Follicle-Stimulating Hormone)
Elevated >25 mIU/mL suggests perimenopause/menopause
FSH / Estradiol
This pair is mainly useful when the story itself contains cycle disruption, menopausal transition, fertility treatment, postpartum change, or clinician concern about estrogen status.
Functional cognitive disorder
A condition where cognitive symptoms are real and distressing but aren't caused by structural brain disease or neurodegeneration. Many patients referred for dementia evaluation actually have FCD.
GABA
Gamma-aminobutyric acid - the brain's main calming neurotransmitter. Balances excitatory signals. Benzodiazepines and alcohol artificially boost GABA, which is why withdrawal causes rebound anxiety and fog.
GAD-7
A short anxiety screener used to estimate symptom burden and track changes over time.
GAD-7 (Anxiety)
Validated anxiety symptom screener used to support differential assessment in clinical context.
Gadolinium
A contrast agent used in MRI scans to highlight areas of inflammation, tumors, or blood-brain barrier breakdown. Used when MS, tumor, or infection is suspected.
gestational diabetes
Diabetes that develops during pregnancy, usually diagnosed at 24-28 weeks via glucose tolerance test. Can affect cognitive function and energy. Blood sugar instability from gestational diabetes can worsen pregnancy brain fog independently of other pregnancy-related cognitive changes.
GFAP
Glial fibrillary acidic protein - a blood biomarker released when astrocytes (brain support cells) are damaged. Elevated levels after head injury help confirm brain involvement. Emerging as a clinical tool for TBI diagnosis and prognosis.
GGT
Gamma-Glutamyl Transferase.
GGT (Gamma-Glutamyl Transferase)
Liver enzyme - elevated with alcohol, medications
GH Stimulation Test
General term for tests that provoke GH release to assess pituitary function. ITT and glucagon stimulation test are the two main options. Required for definitive GHD diagnosis per Endocrine Society guidelines.
GI-MAP
Stool DNA Test.
GI-MAP (Stool DNA Test)
Detects pathogens, parasites, dysbiosis, digestive markers
GLP-1
Glucagon-like peptide-1, a hormone pathway targeted by drugs such as semaglutide and tirzepatide.
Glucose Breath Test
Alternative SIBO test - only detects proximal overgrowth
glutamate
The brain's primary excitatory neurotransmitter. Essential for learning, but excess glutamate is neurotoxic. MSG sensitivity and neuroinflammation can cause glutamate overload.
Glutathione (RBC)
Master antioxidant - low indicates oxidative stress
Glycation
A chemical process where excess glucose sticks to proteins and tissues, contributing to long-term metabolic and vascular damage.
glymphatic
The brain's waste-clearance system, most active during deep sleep.
glymphatic system
The brain's waste-clearance network, active primarily during deep sleep. Alcohol suppresses the deep sleep required for this process, allowing neurotoxic byproducts to accumulate.
glyphosate
The active ingredient in Roundup and other herbicides - the world's most widely used pesticide. Disrupts the gut microbiome by affecting the shikimate pathway in bacteria. Debate continues about neurological effects at typical exposure levels.
GnRH agonist
A medication (e.g., leuprolide, goserelin) that suppresses estrogen production, creating a temporary menopause-like state. Used for endometriosis symptom control but can cause bone density loss and cognitive side effects. Always use with add-back therapy for long-term treatment.
Graded exercise therapy
Starting exercise well below your capacity and increasing by about 10% per week. The strongest evidence-based treatment for central sensitization. The goal is recalibrating the nervous system's threat detection, not building fitness.
Gray Matter
Brain tissue containing neuron cell bodies - where thinking, decision-making, and processing happen. The ENIGMA consortium found eating disorders produce the largest gray matter reductions of any psychiatric disorder. Largely reversible with sustained nutritional rehabilitation.
gray matter remodeling
The reduction of gray matter volume observed during pregnancy, primarily in brain regions involved in social cognition. First documented on MRI by Hoekzema et al. in 2017. This appears to represent neural reorganization for parenting rather than damage - the changes correlate with maternal bonding and may improve efficiency in caregiving circuits.
Grounding Techniques
Sensory-based strategies (such as the 5-4-3-2-1 exercise) used to anchor attention in the present moment during dissociation, flashbacks, or overwhelming arousal. A foundational skill in trauma-informed care.
Growth Hormone (GH)
Hormone produced by the anterior pituitary gland. Stimulates growth, cell reproduction, and metabolic regulation. In adults, it's critical for body composition, energy metabolism, and -- through IGF-1 -- brain function.
Gut
Gut is a nearby overlapping cause that's often worth ruling out when the story pattern is similar.
gut-brain axis
The bidirectional communication network between the gastrointestinal tract and the central nervous system, operating through the vagus nerve, immune signaling, and microbial metabolites.
Hair Cortisol
3-month cortisol average - best for chronic stress assessment
hair mercury
Mercury concentration in hair, reflecting average exposure over the growth period of the hair sample (approximately 1 cm per month).
half-life
The time for caffeine blood levels to drop by half - typically 5-6 hours in most adults, but ranging from 1.5 to 9.5 hours depending on CYP1A2 genotype, pregnancy, and other factors.
Hashimoto
Hashimoto's thyroiditis - an autoimmune condition where the immune system attacks the thyroid gland. The most common cause of hypothyroidism. Detected by elevated TPO antibodies, often years before TSH goes abnormal.
Hashimoto's thyroiditis
The most common autoimmune disease and the most common cause of hypothyroidism. The immune system attacks the thyroid gland, often causing brain fog, fatigue, weight gain, and cold intolerance. Diagnosed by anti-TPO and anti-thyroglobulin antibodies.
HbA1c
Glycated hemoglobin - a blood test measuring average blood glucose over 2-3 months. Normal is below 5.7%, prediabetes is 5.7-6.4%, and diabetes is 6.5% or above. HbA1c shows the average but can miss day-to-day glucose variability that drives cognitive symptoms.
HbA1c + Fasting Insulin
This panel is more useful than HbA1c alone when the story suggests glucose variability, reactive symptoms, or insulin-resistance overlap.
HBOT
Hyperbaric oxygen therapy - breathing pure oxygen in a pressurised chamber. Promotes neuroplasticity and reduces neuroinflammation. The strongest evidence is for post-COVID brain fog (60-session protocols at 2.0 ATA).
Heart Rate Monitoring
Track HR response to position changes
Heavy Metal Panel
Blood/urine screening for lead, mercury, arsenic, cadmium
HEPA
High-Efficiency Particulate Air filter - the main home tool for removing fine particles such as dust, wildfire smoke, and traffic-related PM.
Hepatic encephalopathy
Brain dysfunction caused by liver failure or portal-systemic shunting that allows neurotoxic substances to affect cognition.
hepcidin
Liver hormone that regulates iron absorption. Rises after each iron dose, which is why alternate-day dosing is more efficient than daily dosing.
Herxheimer reaction
A temporary worsening of symptoms that can occur when antibiotics kill bacteria, releasing bacterial toxins. Common in early Bartonella and Lyme treatment. Usually indicates the treatment is working.
Histamine
A biogenic amine released by mast cells and produced by gut bacteria. Acts as neurotransmitter, immune signal, and gastric acid stimulant. DAO enzyme breaks it down in the gut. When histamine input exceeds clearance, overflow causes brain fog, flushing, congestion, headache, and GI symptoms.
Histamine intolerance
Difficulty clearing histamine from the body, often due to low diamine oxidase (DAO) enzyme activity. Aged foods (cheese, wine, fermented foods, cured meats) can trigger symptoms including brain fog, headache, flushing, and GI distress. Often confused with or overlaps with food sensitivity.
HIT-6
Headache Impact Test - a 6-question validated tool measuring the impact of headache on daily function. Score >60 indicates severe impact. Useful for tracking treatment response.
HIT-6 (Headache Impact Test)
HIT-6 captures the full impact of headache beyond just pain - including cognitive function, fatigue, and activity limitation.
HLA-DR
Human Leukocyte Antigen-DR. A genetic marker some CIRS clinicians use to estimate susceptibility to biotoxin illness. The pattern interpretation remains debated outside the Shoemaker framework.
HLA-DR Genotype
24% have mold-susceptible HLA types
HLA-DR/DQ Genotyping
Blood test for immune system genes.
HNMT
Histamine N-methyltransferase - the intracellular enzyme that breaks down histamine inside cells, particularly in the brain and liver. Complements DAO (which works in the gut).
HOMA-IR
Homeostatic Model Assessment for Insulin Resistance. Calculated from fasting insulin and glucose. Above 2.0 indicates insulin resistance. Above 2.9 suggests significant resistance.
homocysteine
A blood marker that can rise when B12, folate, or B6 status is functionally weak even if one isolated vitamin level looks borderline normal.
HPA axis
The hypothalamic-pituitary-adrenal axis - your body's central stress response system. Chronic burnout dysregulates HPA signaling, altering cortisol patterns and contributing to cognitive impairment.
HRT / MHT
Hormone Replacement Therapy / Menopausal Hormone Therapy. Replaces declining estrogen (and progesterone if uterus present). Transdermal estradiol has the best cognitive evidence profile.
HRV
Heart Rate Variability.
HRV (Heart Rate Variability)
Low HRV = sympathetic dominance = chronic stress state
hs-CRP
High-sensitivity C-reactive protein - a blood marker for systemic inflammation. Levels >3mg/L may indicate inflammatory depression subtype requiring different treatment approach.
HSAT
Home Sleep Apnea Test - a portable test that can catch many moderate-severe cases but can miss UARS, mild OSA, or more complex patterns.
Hydrogen (H₂) Breath
Elevated hydrogen indicates bacterial fermentation
Hydrogen Sulfide (H₂S) Breath
Third gas SIBO type - causes diarrhea, sulfur smell
Hydroxychloroquine
An antimalarial medication used as standard treatment for systemic lupus erythematosus. Reduces flares, protects organs, and is recommended for all lupus patients unless contraindicated. May support cognitive function by reducing overall disease activity.
hyperadrenergic POTS
A subtype of POTS with elevated norepinephrine, causing anxiety, tremor, and high blood pressure on standing in addition to tachycardia. May respond to clonidine, guanfacine, or beta-blockers. Diagnosed by standing norepinephrine levels >600 pg/mL.
Hyperandrogenism
Excess male hormones (testosterone, DHEA-S) in women. Causes acne, hair changes, and cognitive effects via androgen receptors in the prefrontal cortex and hippocampus.
Hyperarousal
A threat-state where the nervous system stays keyed up. It can look like scanning, poor sleep, irritability, panic, and difficulty holding onto thoughts.
Hypercalcemia
Abnormally high blood calcium, typically above 10.5 mg/dL. Causes include hyperparathyroidism, cancer, vitamin D toxicity, and certain medications.
hyperventilation
Overbreathing that lowers carbon dioxide levels and can cause dizziness, tingling, and worse cognitive fog through cerebral vasoconstriction.
Hypervigilance
A state of heightened alertness and scanning for threats. Cognitively exhausting and a core contributor to trauma-related brain fog.
Hyperviscosity
Blood that's too thick to flow properly, caused by high M-protein levels. Reduces blood flow to the brain. A medical emergency requiring plasmapheresis.
hypoglossal nerve stimulation
An implanted therapy that stimulates tongue muscles during sleep to reduce airway collapse in selected people who can't tolerate CPAP.
Hypoglycemia
Blood sugar dropping below 70 mg/dL, causing neuroglycopenic symptoms including confusion, difficulty concentrating, shakiness, sweating, and irritability. Below 54 mg/dL, cognitive function is severely impaired. Common in people taking insulin or sulfonylureas.
Hyponatremia
Serum sodium below 135 mEq/L. Can cause confusion, headache, fatigue, and in severe cases, seizures. Common in older adults, people on diuretics, and those who drink excessive plain water without electrolytes.
Hypoperfusion
Reduced blood flow to the brain, often most obvious in upright posture. Causes position-sensitive brain fog, lightheadedness, and cognitive impairment that improves when lying flat.
Hypopituitarism
Deficiency of one or more pituitary hormones. GHD is often one component of broader hypopituitarism -- which is why a full pituitary panel is important.
hyposmia
Reduced sense of smell. Common in CRS, especially with nasal polyps. A 2025 meta-analysis linked olfactory impairment to future cognitive decline.
hypothyroid
Underactive thyroid - insufficient thyroid hormone production.
IBD (Inflammatory Bowel Disease)
Umbrella term for Crohn's disease and ulcerative colitis - chronic autoimmune conditions causing inflammation and tissue damage in the GI tract. Distinct from IBS, which is functional without tissue damage.
ICD-11 QD85
The WHO International Classification of Diseases code for burnout. Classified as an occupational phenomenon, not a medical condition. Defined as chronic workplace stress that hasn't been successfully managed.
IFA
Immunofluorescence Assay - a standard antibody test that uses fluorescent markers to detect antibodies against Bartonella. Has limited sensitivity of approximately 50%, meaning a negative result doesn't rule out infection.
IGeneX Panel
Specialty Lyme testing - detects more strains
IGF-1 (Insulin-like Growth Factor 1)
Protein produced mainly by the liver in response to GH. Crosses the blood-brain barrier and drives neuroplasticity, hippocampal neurogenesis, and neuronal survival. The main mediator of GH's effects on the brain.
IgG food testing
Commercial blood tests that measure IgG antibodies to foods. NOT recommended by the AAAAI, EAACI, or gastroenterology societies. IgG levels reflect food exposure (what you eat regularly), not food sensitivity. High false positive rates lead to unnecessary dietary restriction.
IL-1
Interleukin-1β - a pro-inflammatory cytokine that reduces neurogenesis and disrupts sleep architecture. One of the key drivers of sickness behaviour and brain fog.
IL-6
Interleukin-6 - a pro-inflammatory cytokine. Elevated in Long COVID, chronic stress, and autoimmune conditions. Directly impairs hippocampal function (memory) and prefrontal cortex (focus).
IL-6 (Interleukin-6)
Pro-inflammatory cytokine elevated in Long COVID and chronic inflammation
IMO
Intestinal Methanogen Overgrowth. Methane-producing archaea in the gut, formerly called methane-dominant SIBO. Causes constipation and responds differently to treatment than hydrogen SIBO.
ImPACT
Immediate Post-Concussion Assessment and Cognitive Testing - computerized neurocognitive test used for baseline comparison and post-injury assessment.
Insulin Resistance
A condition where cells respond poorly to insulin, requiring the pancreas to produce more insulin to maintain normal glucose levels. High insulin with normal glucose is the earliest sign. The brain has its own insulin receptors, so insulin resistance directly impairs neuronal function and memory.
Insulin Tolerance Test (ITT)
Gold standard stimulation test for GHD diagnosis. Insulin is given IV to induce hypoglycemia, which should trigger a GH surge. A peak GH below 3 mcg/L confirms severe deficiency. Requires medical supervision.
Interoception
The sense of internal body signals. Many autistic people have reduced interoception, meaning basic needs go unnoticed.
intestinal permeability
The degree to which the gut lining allows molecules to pass through. Increased permeability (sometimes called leaky gut) may allow bacterial products like LPS into the bloodstream, potentially triggering systemic inflammation.
intrinsic factor
Stomach protein required to absorb vitamin B12 from food. Absent in pernicious anemia, which is why oral B12 can't compensate.
ISO
Intestinal Sulfide Overproduction. Hydrogen sulfide-producing bacteria in the gut. Associated with diarrhea and rotten egg odor. The newest recognized SIBO subtype.
k-means clustering
A machine learning algorithm that groups similar data points together. Applied to Long COVID symptoms, it identified 6 distinct phenotypes: sleep-dominant (58% PASC), triple-mix (80%), mental-dominant (66%), asymptomatic (1%), physical-dominant (51%), and physical+mental (85%).
Keto
A very-low-carbohydrate, high-fat diet that shifts the body's primary fuel source from glucose to ketone bodies. Brain fog during keto usually reflects electrolyte depletion or metabolic adaptation, not ketosis itself.
keto flu
A cluster of transient symptoms (headache, fatigue, nausea, brain fog, irritability) commonly reported during the first 1-2 weeks of a ketogenic diet, likely driven by electrolyte shifts and metabolic adaptation rather than being an inevitable consequence of carbohydrate restriction.
keto-adaptation
The metabolic process by which the body upregulates enzymes and transporters to efficiently use ketone bodies as fuel. Typically requires 2-4 weeks, with full metabolic flexibility developing over 4-6 weeks.
ketogenic
A very-low-carbohydrate, high-fat diet that shifts the brain's fuel source from glucose to ketones.
Kidney Function Workup
Kidney-related fog is rarely answered by one creatinine value.
koilonychia
Spoon-shaped nails - a physical sign of iron deficiency where nails become thin, brittle, and concave. Often appears before blood tests flag a problem.
L-theanine
An amino acid found in tea that can soften stress reactivity and promote calm attention without strong sedation in some people.
Lactulose breath test
A diagnostic test for SIBO. Patient drinks lactulose solution, then breath samples are collected over 2-3 hours measuring hydrogen and methane. Positive if hydrogen rises >20ppm in 90 minutes.
Laparoscopy
A minimally invasive surgical procedure using a camera inserted through small incisions. The gold standard for definitive endometriosis diagnosis - lesions can be visualized and excised during the same procedure.
LDN
Low-dose naltrexone - naltrexone at 1–4.5 mg (vs. standard 50 mg) modulates the immune system and reduces neuroinflammation. Used off-label for Long COVID, fibromyalgia, and autoimmune brain fog. Requires prescription.
LDN (low-dose naltrexone)
Naltrexone at doses of 1.5-4.5 mg (much lower than the standard 50 mg dose used for addiction). Emerging evidence suggests anti-inflammatory effects through microglial modulation. Used off-label in some autoimmune conditions with growing but still moderate evidence.
leaky gut
The colloquial term for increased intestinal permeability - gaps in the gut lining that allow inflammatory molecules into the bloodstream, triggering immune activation and brain fog.
Lecanemab
An anti-amyloid antibody FDA-approved for early Alzheimer's disease. The Clarity AD trial showed it reduced cognitive decline by 27% over 18 months.
Lenalidomide (Revlimid)
An immunomodulatory drug (IMiD) used in myeloma treatment and maintenance. Common side effects include fatigue and low blood counts.
leukotriene
Inflammatory mediators produced by mast cells from arachidonic acid. Leukotrienes contribute to bronchoconstriction, mucus production, and inflammation. Urinary leukotriene E4 is one of the biomarkers tested during MCAS workup.
Levine Protocol
Also called the CHOP protocol. A structured recumbent exercise program proven effective for POTS (86% adolescent remission rate). Starts with horizontal exercises (rowing, swimming, recumbent bike) and progressively adds upright training over 3-6 months.
LH
Luteinizing Hormone.
LH (Luteinizing Hormone)
Pituitary hormone - high LH with low T = primary hypogonadism
Light chains
Small protein fragments produced by myeloma cells. Can damage kidneys (cast nephropathy) and are tracked as a disease marker (free light chains/FLC).
lipopolysaccharide
Bacterial fragments (endotoxins) from gram-negative gut bacteria. When they leak through a damaged gut barrier into the bloodstream, they trigger a powerful inflammatory response that reaches the brain.
Loneliness
Subjective feeling of disconnection or inadequate social relationships, regardless of actual social contact. A person can be lonely in a crowd or content alone. Perceived loneliness is a stronger predictor of cognitive decline than objective isolation.
Long COVID / ME/CFS
Long COVID / ME/CFS can contribute to brain fog.
Low-Dose Naltrexone
Naltrexone used at much lower doses than addiction treatment, usually around 0.5 to 4.5 mg, as an off-label immune and neuroinflammation modulator.
LPS
Lipopolysaccharides - bacterial endotoxins that trigger inflammation when they leak from the gut into the bloodstream through a damaged intestinal barrier.
LPS Antibodies
Indicates bacterial endotoxin translocation from gut
Lupus
Systemic lupus erythematosus (SLE), an autoimmune disease where the immune system attacks the body's own tissues. Can affect joints, skin, kidneys, blood, and the nervous system. Brain fog often follows the broader flare-and-remit pattern of disease activity.
Luteal phase
The ~14-day stretch between ovulation and menstruation. This is when PMDD symptoms emerge - progesterone rises, converts to allopregnanolone, and GABA-A receptors destabilize.
Lyme
A tick-borne bacterial infection caused by Borrelia burgdorferi that frequently co-occurs with Bartonella. Shares some neurological symptoms but is more associated with joint pain, erythema migrans rash, and tick-endemic area exposure.
M-protein (paraprotein)
An abnormal antibody produced by myeloma cells. High levels can thicken the blood (hyperviscosity). Tracked as a disease activity marker.
Magnetite
An iron oxide particle identified in polluted air and later found in human brain tissue, helping show that particulate pollution can reach the brain.
mandibular advancement device
An oral appliance that pulls the lower jaw forward to keep the airway more open, often used for mild to moderate obstructive sleep apnea.
MARCoNS
A controversial nasal-colonization concept used inside the Shoemaker protocol, not a routine mainstream mold term.
Masking (camouflaging)
Suppression of natural autistic responses and adoption of neurotypical-appearing alternatives. Primary driver of autistic burnout and cognitive exhaustion.
Maslach Burnout Inventory (MBI)
The gold-standard burnout assessment tool since 1981, measuring three dimensions: emotional exhaustion, depersonalization, and reduced personal accomplishment.
MASLD
Metabolic dysfunction-associated steatotic liver disease (formerly NAFLD) - fatty liver disease driven by metabolic syndrome. Can cause fatigue, brain fog, and cognitive impairment through inflammation, insulin resistance, and impaired detoxification.
mast cell
Immune cells that release histamine and other chemicals during allergic and inflammatory reactions.
mast cell stabilizer
A medication that prevents mast cell degranulation. Examples include cromolyn sodium, ketotifen, and quercetin. Used in MCAS to reduce the frequency and severity of flares.
MBSR
Mindfulness-Based Stress Reduction, an 8-week structured program that combines meditation, body awareness, and gentle movement.
MCAS
Mast cell activation syndrome - mast cells release excessive histamine and other mediators, causing brain fog, flushing, hives, GI symptoms, and reactions to foods/chemicals.
MCV
Mean Corpuscular Volume.
MCV (Mean Corpuscular Volume)
Elevated MCV suggests B12/folate deficiency or alcohol
MDQ
Mood Disorder Questionnaire. A bipolar-spectrum screening tool used to decide whether a fuller bipolar assessment is worth doing.
Medication Brain Fog
Cognitive slowing caused or worsened by prescription drugs, over-the-counter medications, nutrient depletion from long-term medication use, or interaction burden from several drugs taken together.
Medication Depletion Panel
Some medications do not cause fog directly so much as they quietly deplete the nutrients the brain depends on.
Medication Review
Identify fog-causing meds: benzos, anticholinergics, etc.
Medication Therapy Management
A structured medication review, often led by a pharmacist, looking for interactions, duplications, side effects, and opportunities to simplify the regimen.
Melatonin
A hormone involved in sleep timing. Evening light exposure can delay the normal melatonin rise that helps prepare the brain for sleep.
Melatonin / DLMO
Melatonin is a hormone involved in sleep timing. DLMO means dim-light melatonin onset and is a marker of circadian phase.
Menopause
The permanent end of menstrual cycles. PMDD resolves after menopause, but perimenopause (the transition) often worsens PMDD as hormone swings become more erratic.
Mercury
Mercury is a nearby overlapping cause that is often worth ruling out when the story pattern is similar.
Mercury / Heavy Metal Toxicity
Mercury / Heavy Metal Toxicity can contribute to brain fog.
metabolic flexibility
The ability to switch efficiently between glucose and fat/ketone oxidation as fuel sources. People with good metabolic flexibility can tolerate dietary shifts with fewer cognitive symptoms.
Metabolic vascular
A brain-fog pattern driven by accumulated metabolic and blood-vessel burden rather than one isolated trigger.
Metformin
First-line medication for Type 2 diabetes that reduces liver glucose production and improves insulin sensitivity. Important cognitive side effect: long-term use depletes vitamin B12, which causes its own brain fog independent of glucose levels. B12 should be monitored annually in metformin users.
Methane (CH₄) Breath
Elevated methane = IMO (intestinal methanogen overgrowth)
methylmalonic
Methylmalonic acid (MMA) - a more sensitive marker for B12 deficiency than serum B12 alone. Elevated MMA indicates functional B12 deficiency even when serum B12 is borderline normal.
Methylmalonic acid
A functional vitamin B12 marker. Elevated methylmalonic acid can indicate tissue-level B12 deficiency even when serum B12 still looks normal.
methylmercury (MeHg)
The organic form of mercury found in fish and seafood.
MGUS
Monoclonal Gammopathy of Undetermined Significance. A precursor condition to myeloma. Doesn't require treatment but needs monitoring for progression.
microbiome
The community of trillions of bacteria, fungi, and viruses living in your gut that influence digestion, immunity, and brain function.
microglia
The brain's resident immune cells.
microglial activation
Microglia are the brain's immune cells. After TBI, they activate to clear damage but can become chronically overactive, maintaining neuroinflammation months or years after the initial injury. A target for anti-inflammatory interventions.
microglial priming
A state where microglia (brain immune cells) become sensitized by prior inflammation, making them react more strongly to future triggers. This may explain why some people develop persistent brain fog after infections - their microglia remain in a 'hair-trigger' state.
Microvascular damage
Damage to small blood vessels, relevant in diabetes and hypertension because the brain depends on intact microcirculation.
MIDAS
Migraine Disability Assessment Score - a validated questionnaire that quantifies migraine-related disability across work, household, and social domains over the past 3 months. Grades I-IV.
MIDAS (Migraine Disability Assessment)
MIDAS translates subjective migraine burden into a standardized disability grade.
midodrine
An alpha-1 agonist medication that constricts blood vessels, raising blood pressure. Used in orthostatic hypotension to prevent blood pooling when standing.
Migraine
A primary neurological disorder involving episodic headache, sensory sensitivity, aura, nausea, and cognitive disruption. Brain fog can occur before, during, or after the headache phase.
mitochondri
Mitochondria - the energy-producing structures inside every cell. When they malfunction (from inflammation, nutrient deficiency, or viral damage), cells can't produce enough ATP (energy). Result: fatigue and brain fog.
MMA
Methylmalonic acid. A confirmatory marker that helps catch functional B12 deficiency when serum B12 is borderline.
MMA (Methylmalonic Acid)
Elevated MMA confirms B12 deficiency at tissue level
MMC
The Migrating Motor Complex - your gut's 'cleaning wave' that sweeps bacteria and debris from the small intestine. It only activates during fasting (90-120 min after eating). Frequent snacking prevents MMC firing, promoting bacterial overgrowth.
MMP-9
Matrix Metalloproteinase-9. An enzyme marker of inflammation and tissue remodeling. Elevated in many inflammatory conditions, not specific to mold or CIRS.
MMP-9 (Matrix Metalloproteinase-9)
Elevated in active mold exposure and inflammation
MoCA
Montreal Cognitive Assessment. A 10-minute screening test for mild cognitive impairment, more sensitive than the older MMSE. Score below 26/30 suggests impairment warranting further evaluation.
MOH
Medication overuse headache - chronic daily headache caused by taking acute headache medications (triptans, NSAIDs, paracetamol) too frequently. Risk threshold: >10 days/month for triptans, >15 days/month for simple analgesics.
Mold
Microscopic fungi that grow in damp indoor environments and can worsen respiratory, allergic, and sometimes cognitive symptom patterns when exposure is ongoing.
mononucleosis
Infectious mononucleosis (mono) - the acute illness caused by primary EBV infection. Common in teens and young adults. Symptoms include extreme fatigue, sore throat, swollen lymph nodes, and fever.
MRI
Diffusion Tensor Imaging.
MS
MS can contribute to brain fog.
MSH
Melanocyte-Stimulating Hormone. A regulatory hormone often low in CIRS patients per the Shoemaker model. Not a routine test in mainstream practice.
MSH (Melanocyte-Stimulating Hormone)
Low MSH = impaired immune regulation in CIRS
MSPSS
Multidimensional Scale of Perceived Social Support - a 12-item questionnaire measuring support from family, friends, and significant others. Ranked 13th predictor in Long COVID ML classification. Low social support = measurably worse outcomes. Treatable via social prescribing and support groups.
mTBI
Mild traumatic brain injury - the clinical classification for most concussions. 'Mild' refers to the initial injury severity, not the symptoms that follow. Persistent symptoms after mTBI can be severe and disabling.
mucolytic
A substance that thins mucus, making it easier to clear. NAC (N-acetyl cysteine) is the most common mucolytic supplement.
Multiple myeloma
A blood cancer of plasma cells in the bone marrow. These abnormal cells produce monoclonal protein (M-protein) and crowd out normal blood cell production.
Mycotoxin
A toxin produced by some molds. Exposure concerns are most relevant in water-damaged environments and should be handled with careful, non-sensational wording.
Myo-inositol
A supplement that acts as a second messenger in insulin signaling. Evidence from 26+ RCTs shows it improves insulin sensitivity in PCOS comparably to metformin with fewer side effects.
N-Methylhistamine (24hr Urine)
Histamine metabolite - more stable than plasma histamine
N3 sleep
Deep slow-wave sleep, the stage most associated with feeling physically restored and mentally clearer the next day.
NAC
N-acetyl cysteine - an amino acid supplement that replenishes glutathione (the body's master antioxidant), reduces neuroinflammation, and helps break down mucus. Dose: 600–1,200 mg/day.
NAD+
Nicotinamide adenine dinucleotide - a coenzyme essential for mitochondrial energy production. Depleted after TBI through PARP-1 overactivation. NAD+ precursors (nicotinamide riboside) are being investigated as neuroprotective supplements.
NAFLD/MASLD
Fatty liver disease in its older and newer naming systems.
NASA Lean Test
A simple orthostatic screening test: stand leaning against a wall (heels 6 inches from wall) for 10 minutes.
nasal endoscopy
In-office ENT procedure using a thin camera to visualise the inside of the nose and sinuses. Takes about 5 minutes. Gold standard for structural assessment.
nasal polyps
Noncancerous growths on the lining of nasal passages or sinuses that block airflow and drainage. Associated with chronic inflammation.
NCGS
Non-Celiac Gluten Sensitivity. A condition where gluten ingestion causes intestinal and extra-intestinal symptoms (including brain fog) without celiac disease or wheat allergy. Formal diagnosis requires double-blind gluten challenge (Salerno criteria, 2015). Mechanisms may involve FODMAPs, innate immune responses, or both.
NEAT
Non-exercise activity thermogenesis - the energy expended through daily activities that aren't structured exercise (walking to the kitchen, fidgeting, standing). NEAT can account for 15-50% of total daily energy expenditure and contributes to cognitive benefits independently of formal exercise.
Nephrologist
A physician who specializes in kidney disease, electrolyte problems, and dialysis-related care.
Neuroception
The nervous system's unconscious detection of safety or danger in the environment. Faulty neuroception from trauma means the body reads safe situations as threatening, keeping the fog-producing threat response active.
Neurodivergent
Umbrella term for neurological differences including autism, ADHD, dyslexia. Frames these as natural variations.
neurofilament light (NfL)
A protein released from damaged nerve fibers (axons) into the blood. Elevated NfL after concussion indicates axonal injury. Used as a biomarker for injury severity and recovery tracking.
neurogenesis
The creation of new neurons, primarily in the hippocampus (memory centre).
Neuroglycopenic
Symptoms caused by the brain not getting enough usable glucose, such as confusion, slowed thinking, or difficulty concentrating.
neuroinflammation
Inflammation in the brain and nervous system, often used to describe one of the pathways by which pollution and irritant exposure can worsen cognition.
Neurological red flags
Warning signs that cognitive symptoms may have a dangerous underlying cause requiring urgent medical evaluation, such as stroke, brain tumor, neurodegenerative disease, or normal-pressure hydrocephalus.
Neuropathic POTS
A subtype of POTS caused by damage to small fiber nerves controlling blood vessels. Often associated with autoimmune conditions. May respond to IVIG or other immunomodulatory treatments. Diagnosed via skin biopsy showing reduced nerve fiber density.
Neuroplasticity
The brain's ability to reorganize and form new connections. MRI studies show burnout causes structural brain changes that are partially reversible with treatment - evidence that the brain can recover from sustained overload.
Neuropsych Testing
Tests memory, attention, executive function, processing speed
Neuropsychological Evaluation
Gold standard for ADHD and cognitive dysfunction
neuropsychological testing
Standardized objective cognitive assessment measuring processing speed, attention, memory, and executive function. More useful than MRI for detecting post-concussion cognitive deficits.
neurosteroid
Steroid hormones produced in the brain that modulate neurotransmitter receptors, particularly GABA. Allopregnanolone is the key neurosteroid implicated in PMDD - abnormal sensitivity to its fluctuations may cause luteal-phase symptoms.
NF-kB
Nuclear factor kappa-B - a protein complex that controls inflammation gene expression. When chronically activated, it drives sustained neuroinflammation. Curcumin, omega-3s, and NAC help modulate it.
Nicotine
Nicotine can contribute to brain fog.
Nitrogen dioxide
A combustion-related gas produced by traffic and gas stoves. Indoors it can worsen headaches, irritation, and air-quality-driven brain fog.
NLR
Neutrophil-to-Lymphocyte Ratio - a calculated inflammation marker from a standard CBC.
NLR (calculated)
Neutrophil-to-lymphocyte ratio derived from CBC differential as an inflammatory context signal.
NMDA receptor
A receptor involved in memory, learning, and brain signaling. Anti-NMDA receptor encephalitis can look like psychosis or severe psychiatric illness.
NMN
Nicotinamide mononucleotide - a precursor to NAD+, the coenzyme essential for mitochondrial energy production. Emerging evidence for cognitive benefits, particularly in age-related and post-viral brain fog.
Nociplastic pain
A third pain mechanism (alongside nociceptive and neuropathic) where the nervous system generates and amplifies pain without tissue damage or nerve injury. Fibromyalgia is the prototypical nociplastic pain condition.
Non-celiac gluten sensitivity (NCGS)
A condition where gluten ingestion causes symptoms (including brain fog) in people who don't have celiac disease or wheat allergy. Formal diagnostic criteria (Salerno 2015) require double-blind gluten challenge. A Lancet Neurology paper showed gluten sensitivity can affect the brain directly, even without GI symptoms.
Non-stimulant medication
ADHD treatments such as atomoxetine, guanfacine XR, or clonidine XR that don't use stimulant mechanisms.
noradrenaline
Also called norepinephrine. The neurotransmitter that governs alertness. In hyperadrenergic POTS, excessive noradrenaline causes anxiety, tremor, and palpitations alongside orthostatic symptoms.
norepinephrine
A neurotransmitter and stress hormone that governs alertness and attention. Too little = foggy and fatigued. Too much = anxious and scattered. Cold exposure triggers a reliable spike.
Notification
A push alert, banner, vibration, or badge that pulls attention toward a device and can create interruption costs even when ignored.
NPH
Normal-pressure hydrocephalus. A treatable condition where excess cerebrospinal fluid causes the classic triad of cognitive impairment, gait difficulty, and urinary incontinence. Shunt surgery can restore function.
NPSLE
Neuropsychiatric systemic lupus erythematosus - when lupus directly affects the central nervous system. Can cause cognitive dysfunction, headaches, seizures, psychosis, and mood changes. Affects up to 40% of SLE patients and requires specific evaluation and treatment beyond standard lupus management.
Nrf2
A protein that activates your body's antioxidant defence genes. Sulforaphane (from broccoli sprouts), curcumin, and exercise activate Nrf2. It's one of the most powerful natural anti-inflammatory pathways.
NRT
Nicotine replacement therapy.
NSDR
Non-sleep deep rest. A guided rest practice used to downshift arousal without necessarily falling asleep.
Nutrient
Nutrient is a nearby overlapping cause that's often worth ruling out when the story pattern is similar.
Nutrient deficiency
A short way of saying the brain and body are missing something they need to function well, such as iron, B12, folate, vitamin D, or magnesium.
nutritional ketosis
A metabolic state where blood ketone levels reach 0.5-3.0 mmol/L through dietary carbohydrate restriction, distinct from diabetic ketoacidosis (which involves dangerously high ketones above 10 mmol/L alongside high blood glucose).
ODI
Oxygen Desaturation Index - the number of times oxygen drops during sleep, which can matter even when people focus only on the AHI.
omega-3 confounding
A key challenge in mercury research: people with higher mercury levels typically eat more fish, which also provides neuroprotective omega-3 fatty acids. This makes it difficult to separate mercury's harmful effects from fish's beneficial effects in observational studies.
Omega-6:3 ratio
Fatty-acid balance marker used to contextualize inflammatory dietary patterns.
Opioid-induced hyperalgesia
A paradoxical increase in pain sensitivity caused by long-term opioid use. The opioids that are supposed to reduce pain actually increase the nervous system's sensitivity over time, worsening both pain and cognitive fog.
organophosphate
A class of pesticides that inhibit acetylcholinesterase, disrupting nervous system function. Common in agriculture. Acute exposure causes cholinergic crisis; chronic low-level exposure is linked to cognitive impairment, neuropsychiatric symptoms, and brain fog.
Orthorexia
Not yet a formal diagnosis but increasingly recognized: an obsessive focus on 'healthy' or 'clean' eating that becomes restrictive enough to cause nutrient deficiencies. Can cause brain fog when entire food groups are eliminated.
Orthostatic BP Measurement
Blood pressure change from lying to standing
orthostatic intolerance
Symptoms triggered by upright posture: dizziness, brain fog, palpitations, nausea, weakness. Umbrella term that includes POTS, orthostatic hypotension, and other conditions where the body cannot properly regulate blood flow when vertical.
orthostatic vital signs
Blood pressure and heart rate measurements taken while lying down and after standing. Used to screen for orthostatic hypotension (BP drop 20+ mmHg) and POTS (HR rise 30+ bpm).
Orthostatic Vitals
Combined HR and BP measurements with position
OSA
Obstructive sleep apnea, a common metabolic-syndrome overlap that independently causes cognitive impairment.
Osteocalcin
A hormone produced by bones that crosses the blood-brain barrier and affects cognition. Eating disorders that cause bone loss (especially anorexia nervosa) may impair cognitive function through this bone-brain pathway. An emerging research area.
P300
An event-related potential (brain response) occurring approximately 300 milliseconds after a stimulus, reflecting cognitive processing speed and attention allocation. Significantly delayed in brain fog patients (Fabio 2024: F(1,39)=16.11, p<0.01), meaning the brain takes measurably longer to classify relevant information. Persists at 8 months post-infection.
P300 ERP
Event-related potential index of processing speed and attention timing.
pagophagia
Compulsive ice craving strongly associated with iron deficiency. A form of pica that often resolves when iron stores are restored.
Pain
Chronic pain, particularly neuropathic pain and foot/shin pain, is a common feature of Bartonella infection due to vasculitis and small fiber neuropathy affecting peripheral nerves and blood vessels.
Pain catastrophizing
A pattern of rumination, magnification, and helplessness in response to pain. Measured by the Pain Catastrophizing Scale (PCS). Higher catastrophizing amplifies both pain intensity and cognitive fog. CBT and EAET can reduce it.
Pain neuroscience education (PNE)
Educational approach that teaches patients about the neuroscience of pain, including central sensitization. Understanding that pain can be driven by nervous system sensitivity rather than tissue damage changes pain processing and reduces both pain and disability.
Pain Scales
Standardized pain assessment tools
parasympathetic
The 'rest-and-digest' branch of the autonomic nervous system, controlled primarily by the vagus nerve. Activating it reduces heart rate, lowers inflammation, and supports cognitive recovery.
parathyroid hormone
PTH, a hormone that rises when vitamin D or calcium is low. Elevated PTH with low vitamin D is a key clinical finding called secondary hyperparathyroidism.
Parathyroid hormone (PTH)
A hormone produced by the parathyroid glands that regulates blood calcium levels. PTH pulls calcium from bones, increases calcium absorption from the gut, and reduces calcium loss in the kidneys.
Parathyroidectomy
Surgical removal of one or more parathyroid glands. For PHPT, minimally invasive focused parathyroidectomy targets the single overactive gland. Outpatient procedure, 20-60 minutes, >95% cure rate.
PASC
Post-Acute Sequelae of SARS-CoV-2 infection - the formal medical term for Long COVID.
PCFS
Post-COVID Functional Scale - a validated measure of functional status after COVID-19, grading ability to perform daily activities. Ranked #1 predictor (importance 0.0766) in ML classification - how much you can do is the strongest signal of Long COVID severity.
PCL-5
PTSD Checklist for DSM-5. A screening and tracking tool used when trauma symptoms may be driving cognition problems.
PCOS (Polycystic Ovary Syndrome)
A metabolic-hormonal condition affecting ~10% of women. Involves insulin resistance, androgen excess, and chronic inflammation. Not just a reproductive condition - affects the brain directly.
Pcs
Post-concussion syndrome - a persistent cluster of cognitive, sensory, and neurological symptoms that continue after a concussion or mild traumatic brain injury.
PEA
Palmitoylethanolamide - a naturally occurring fatty acid with anti-inflammatory and neuroprotective properties. Works by calming overactive microglia. Dose: 600–1,200 mg/day. Well-tolerated with few interactions.
Pelvic floor physical therapy
Specialized physiotherapy targeting the muscles of the pelvic floor. Can help with chronic pelvic pain, painful intercourse, and bladder/bowel symptoms in endometriosis. An underutilized complementary approach.
PEM
Post-exertional malaise - the hallmark symptom of ME/CFS and many Long COVID cases.
Perimenopause
The transition period before menopause when hormone levels fluctuate. Can start in late 30s to mid-40s. Often when cognitive symptoms first appear - sometimes years before hot flashes.
perinatal
The period from pregnancy through approximately one year postpartum. Perinatal mood disorders (depression and anxiety during this window) affect 15-20% of women and can present as brain fog, poor concentration, and difficulty thinking clearly. ACOG recommends screening at least once during the perinatal period.
Perioperative Neurocognitive Disorder (PND)
Umbrella term for cognitive changes associated with surgery and the broader perioperative period, including acute delirium and longer postoperative cognitive decline.
pernicious anemia
Autoimmune destruction of stomach parietal cells that make intrinsic factor, causing B12 malabsorption. Requires B12 injections rather than oral supplementation.
Pesticides
Pesticides can contribute to brain fog.
PHES
Psychometric Hepatic Encephalopathy Score, a validated paper-based test battery for covert hepatic encephalopathy.
Phosphatidylserine
A phospholipid supplement sometimes used to blunt stress reactivity, especially when the problem feels like a high-alert response to mental or exercise load.
photobiomodulation
Using specific wavelengths of red or near-infrared light to stimulate mitochondrial function in brain cells. Transcranial devices (worn on the head) have shown cognitive improvements in Long COVID trials.
PHQ-9
Patient Health Questionnaire-9: a free, validated 9-question depression screening tool. Score >=10 suggests moderate depression. Question 9 screens for suicidal thoughts.
pituitary
A small gland at the base of the brain that controls hormones including cortisol, thyroid, growth hormone, and sex hormones. Can be damaged by moderate-to-severe traumatic brain injury in 20-40% of cases.
Pituitary Gland
Pea-sized gland at the base of the brain that produces GH, TSH, ACTH, LH, FSH, and prolactin. Damage from TBI, tumors, surgery, or radiation can impair one or more hormone outputs.
Plasma Histamine
Direct histamine measurement - elevated causes brain fog, flushing
PLR
Platelet-to-Lymphocyte Ratio - a blood inflammation marker calculated from CBC.
PLR (calculated)
Platelet-to-lymphocyte ratio derived from CBC values used as an adjunct inflammatory/vascular signal.
PM2.5
Fine particulate matter 2.5 microns or smaller. These particles are small enough to penetrate deeply into the body and are one of the main air-pollution brain-fog concerns.
PM2.5 Monitoring
PM2.5 monitoring helps when the trigger looks more like smoke, traffic, cooking, candles, or wildfire days than stale air alone.
PM2.5 Sensor
Fine particulate matter - affects brain inflammation
PMDD
Premenstrual dysphoric disorder - a DSM-5 neuropsychiatric condition where normal hormonal fluctuations trigger severe cognitive, emotional, and physical symptoms during the luteal phase. Not the same as PMS.
PNE
Pain Neuroscience Education - teaching patients how the nervous system processes and amplifies pain. Understanding central sensitization itself is therapeutic and associated with meaningful reductions in pain and disability.
PNIF
Peak nasal inspiratory flow - an objective measure of nasal airway patency. Low PNIF indicates significant nasal obstruction.
polypharmacy
The concurrent use of 5 or more medications. Polypharmacy raises the odds of duplication, interaction burden, and cognitive side effects.
polysomno
Polysomnography - an overnight sleep study that monitors brain waves, breathing, oxygen levels, and muscle activity. The gold standard for diagnosing sleep apnea, UARS, and other sleep disorders.
polysomnography
An overnight in-lab sleep study that monitors brain waves, breathing, oxygen levels, heart rhythm, and body position.
Polysomnography (Sleep Study)
Gold standard for sleep apnea diagnosis
polyvagal theory
A framework about vagal-state regulation used to describe shifts between safety, mobilization, and shutdown. Useful conceptually, but not a standalone diagnosis.
Post surgical
Brain-fog symptoms that began after an operation and are being interpreted through a surgical recovery lens.
Post-exertional malaise
A disproportionate crash 24-48 hours after physical or mental effort. A hallmark of ME/CFS and Long COVID but NOT typically present in burnout. Its presence suggests a post-viral or neuroimmune condition rather than burnout.
Post-exertional malaise (PEM)
Disproportionate worsening of symptoms after physical or cognitive exertion, lasting more than 24 hours. A hallmark of ME/CFS that distinguishes it from fibromyalgia. If exercise consistently worsens fog the next day, ME/CFS overlap should be evaluated.
postdrome
The 'migraine hangover' phase lasting 24-48 hours after the headache resolves. Characterized by brain fog, fatigue, difficulty concentrating, and mood changes. This is part of the migraine attack, not a separate problem.
Postmenopause
The stage after 12 consecutive months without a period. Brain fog typically improves during this stage as the brain adapts to stable (lower) hormone levels.
Postoperative Cognitive Dysfunction (POCD)
Older term for measurable cognitive decline after surgery. The newer consensus language places this under the broader PND framework.
Postpartum
The recovery period after childbirth, when dramatic hormone shifts, sleep disruption, blood loss, nutrient depletion, mood changes, and thyroid problems can all combine to impair cognition.
postpartum thyroiditis
Inflammation of the thyroid gland occurring in 5-10% of women in the months after childbirth. Has two phases: a brief hyperthyroid phase followed by hypothyroidism. 20-30% develop permanent hypothyroidism.
Postprandial
After a meal. Postprandial glucose refers to blood sugar levels 1-3 hours after eating. Postprandial spikes and crashes are a primary driver of acute diabetes-related brain fog and can be reduced by eating protein first and walking after meals.
POTS
Postural Orthostatic Tachycardia Syndrome - an autonomic dysfunction causing rapid heart rate on standing. Bartonella can cause POTS-like symptoms through vascular inflammation and autonomic nervous system disruption.
Prediabetes
HbA1c between 5.7% and 6.4%, or fasting glucose between 100-125 mg/dL. The intervention window where lifestyle changes have the highest return. Research shows cognitive decline begins in this range, not just after diabetes diagnosis.
preeclampsia
A pregnancy complication involving high blood pressure and protein in urine, typically developing after 20 weeks. Can cause severe headache, vision changes, confusion, and upper abdominal pain. A medical emergency that requires urgent evaluation. May affect long-term cognitive health.
prefrontal cortex
The front region of your brain responsible for planning, decision-making, working memory, and focus.
Pregnancy
Pregnancy-related brain fog refers to cognitive changes during pregnancy that can affect memory, attention, and mental stamina. Documented on MRI as gray matter volume reductions in regions involved in social cognition. Most women report cognitive recovery within months of delivery.
Pregnenolone
A steroid precursor sometimes marketed for memory, mood, or hormonal support. It is hormone-adjacent and should be treated more cautiously than a standard over-the-counter supplement.
Premature ovarian insufficiency (POI)
Loss of ovarian function before age 40. Associated with higher cognitive and dementia risk. HRT recommended to at least average age of natural menopause (~51) per ESHRE/ASRM guidelines.
prenatal
Before birth; relating to pregnancy. Prenatal vitamins, prenatal care, and prenatal screening are standard components of pregnancy management. Prenatal iron and thyroid status directly affect both maternal cognition and fetal brain development.
presyncope
The feeling of nearly fainting - lightheadedness, tunnel vision, grey-outs, and warmth - without fully losing consciousness. A strong clue for hypoperfusion.
Primary hyperparathyroidism (PHPT)
A condition where one or more parathyroid glands overproduce PTH, causing chronically elevated blood calcium. Most commonly caused by a single benign adenoma (80-85% of cases).
Problematic smartphone use
A pattern of phone use that has become compulsive, impairing, or hard to control despite clear downsides.
prodrome
The earliest phase of a migraine attack, occurring hours to days before headache. Symptoms include brain fog, fatigue, mood changes, food cravings, and yawning. Recognizing prodrome allows earlier treatment.
Progesterone
Hormone that supports sleep and airway tone. Declines before estrogen during perimenopause. Micronized progesterone (body-identical) is preferred over synthetic progestins (MPA) for cognitive safety.
Prokinetic
A medication or supplement that stimulates gut motility (movement). Used in SIBO maintenance to keep the MMC firing and prevent recurrence. Examples: low-dose erythromycin, prucalopride, ginger.
Prolactin
Elevated prolactin suppresses testosterone
Prolonged Exposure
An 8-15 session psychotherapy for PTSD involving gradual, repeated engagement with trauma-related memories, feelings, and situations that are being avoided. One of the most studied and recommended first-line PTSD treatments.
PROMIS cognitive
Patient-Reported Outcomes Measurement Information System Cognitive Function - a validated questionnaire measuring subjective cognitive complaints. Ranked 5th predictor (importance 0.0626) in Long COVID ML classification. Gives doctors a validated number instead of 'I feel foggy.'
Prostaglandin D2
Mast cell mediator - elevated in MCAS and allergic reactions
Provoked Challenge Test
DMSA/DMPS chelation challenge - controversial but used
Pseudodementia
Cognitive impairment caused by depression that can mimic neurodegenerative dementia. Unlike true dementia, pseudodementia typically improves with antidepressant treatment.
PSG
Sleep Study.
PSQI
Pittsburgh Sleep Quality Index - a standard questionnaire that helps quantify how restorative or disrupted sleep has felt over the last month.
PSS-10
Perceived Stress Scale - a 10-item validated questionnaire measuring stress levels. Ranked 11th predictor (importance 0.0421) in Long COVID ML classification. Score 14-26 = moderate stress, 27+ = high. High stress is as predictive as clinical measures like headache.
Psychiatric conditions
A broad label for conditions like bipolar disorder, PTSD, OCD, psychosis, dissociation, and severe anxiety when the illness itself, the surrounding sleep loss, or the treatment burden can impair cognition.
PTLDS
Post-Treatment Lyme Disease Syndrome. Persistent symptoms of fatigue, pain, and cognitive difficulty that continue after standard antibiotic treatment for Lyme disease. The cause is debated and treatment approaches differ between IDSA and ILADS guidelines.
PTSD
Post-traumatic stress disorder. A trauma response where the nervous system remains locked into threat surveillance, causing brain fog through hypervigilant scatter, dissociation, or trigger-linked shutdown.
pyrethroid
A class of synthetic pesticides derived from chrysanthemum flowers. Used in household insect sprays, pet treatments, and agriculture. Generally considered safer than organophosphates but can cause neurological symptoms at high exposure.
QbTest
Computer-based attention and impulsivity testing
QEEG
Quantitative electroencephalography. A processed EEG map that compares brain-wave patterns against a normative database and is sometimes used before neurofeedback.
quantitative EEG
Digital analysis of brain electrical activity patterns, breaking the raw EEG signal into frequency bands (delta, theta, alpha, beta, gamma) to quantify brain function. Research shows measurable differences in brain fog patients vs healthy controls: reduced alpha (8-13 Hz) and increased theta (4-7 Hz). Currently research-grade only - not yet a standard clinical diagnostic for brain fog.
Quantitative EEG (qEEG)
Electrophysiology-based mapping sometimes used in specialist cognitive evaluation.
RAADS-R
80-item self-report autism screening tool. Score 65+ suggests autism. Not diagnostic on its own.
random forest
A machine learning algorithm that builds multiple decision trees and combines their predictions. It is commonly used to rank variables, classify groups, or estimate risk from many overlapping features.
Rapid Alternating Movement
Bedside coordination screen assessing dysdiadochokinesia and cerebellar-motor timing.
RBC
Glutathione.
RBC Magnesium
Red blood cell magnesium test. More reliable than serum magnesium for detecting true deficiency because serum reflects only 1% of total body magnesium stores.
RDI
Respiratory Disturbance Index - a broader count that can include arousal-based breathing events beyond classic apneas and hypopneas.
Reactive Hypoglycemia
Blood sugar dropping 2-4 hours after eating, typically following a post-meal glucose spike. Causes a crash pattern of fog, shakiness, and irritability that's relieved by eating. Common in insulin resistance and early diabetes, and a key pattern distinguishing diabetes fog from other causes.
Reduced personal accomplishment
The third MBI dimension - a sense of ineffectiveness and lack of achievement at work. People feel incompetent despite objective evidence of past competence.
Refeeding Syndrome
A potentially fatal condition that occurs when nutrition is restarted after prolonged fasting or malnutrition. Rapid electrolyte shifts - especially phosphate - can cause confusion, seizures, and cardiac complications. This is why refeeding must be medically supervised.
REM sleep
Rapid eye movement sleep, a stage tied to memory, dreaming, and emotional processing. Repeated interruptions here can leave mornings fuzzy.
REM-predominant OSA
A pattern where breathing events cluster more heavily in REM sleep, which can make a person feel foggy even when part of the night looked milder.
Remediation
Fixing the moisture problem and removing or containing damaged material so mold growth stops returning.
RERA
Respiratory effort-related arousal, a subtle sleep-breathing event that can fragment sleep without classic severe apnea.
RERAs
Respiratory effort-related arousals - brief awakenings caused by increased breathing effort that don't meet the criteria for apnea. Cause fragmented sleep and daytime fog. Many sleep labs don't score them unless asked.
reticulocyte count
Measurement of immature red blood cells released from bone marrow. Indicates how actively your body is making new red blood cells in response to anemia.
Reverse T3
An inactive thyroid hormone metabolite sometimes checked when thyroid symptoms persist despite a basic thyroid panel that looks acceptable.
Rheumatoid Factor
Elevated in rheumatoid arthritis and other autoimmune conditions
rhinitis medicamentosa
Rebound nasal congestion caused by overuse of decongestant sprays (Afrin/oxymetazoline) beyond 3 consecutive days.
Rhodiola rosea
An adaptogenic herb studied mainly for stress-related fatigue and strain. It is better framed as a fatigue-support adjunct than as proof of “adrenal fatigue.”
Rifaximin
A non-absorbable antibiotic that stays in the gut and targets small intestinal bacteria. The first-line prescription treatment for SIBO, especially hydrogen-dominant cases.
Romberg Balance
Patient-facing Romberg balance exam route covering the bedside balance screen often recommended in neurological or vestibular context.
Romberg Balance (eyes closed)
Balance and proprioception screen used in vestibular and neurological exam context.
Rome IV criteria
The current international diagnostic criteria for functional gastrointestinal disorders including IBS, based on symptom patterns rather than test results.
Rotterdam Criteria
The diagnostic standard for PCOS: need 2 of 3 features - irregular/absent periods, clinical or biochemical hyperandrogenism, polycystic ovaries on ultrasound.
RYGB (Roux-en-Y Gastric Bypass)
The most common malabsorptive bariatric procedure. Creates a small stomach pouch and bypasses the duodenum and proximal jejunum, reducing nutrient absorption.
Salivary cortisol
A saliva-based cortisol measurement often used in stress research and late-night Cushing screening because it is easy to collect at home.
SCAT6
Sport Concussion Assessment Tool, 6th edition (2023). Standardized assessment for evaluating concussion including symptom checklist, cognitive testing, and balance assessment.
SCFA
Short-chain fatty acids - metabolites produced by gut bacteria from dietary fibre (butyrate, propionate, acetate). They strengthen the gut barrier, reduce inflammation, and support brain function.
Screen time
Total time spent using phones, tablets, computers, or other screens. On this page, the more useful clue isn't the raw total alone but whether high-screen days map to worse symptoms.
Screen Time Audit
Digital wellness assessment
SDMT
The Symbol Digit Modalities Test.
Sedentary
Extended physical inactivity that reduces cerebral blood flow, BDNF production, and glucose regulation, contributing to cognitive sluggishness that typically reverses with consistent movement.
Sensory overload
When sensory input exceeds processing capacity. In autistic people, the threshold is often lower and drops further during burnout.
septoplasty
Surgery to straighten a deviated nasal septum, improving airflow through the nose.
seroconversion
The point when blood tests first detect antibodies to a virus. For EBV, seroconversion means VCA IgG becomes positive after initial infection.
serotonin
A neurotransmitter regulating mood, sleep, and gut motility. About 95% of the body total is produced in the gut, though peripheral serotonin doesn't directly cross the blood-brain barrier.
Serum Creatinine
Core kidney marker used to estimate filtration, especially when interpreted with eGFR rather than as a standalone number.
Serum Osmolality
Measure of dissolved particles in blood (normal 275-295 mOsm/kg). Helps distinguish types of hyponatremia and assess overall fluid balance.
Serum Potassium
Abnormal potassium affects nerve and muscle function
Serum Sodium
Core electrolyte marker that may affect fatigue, cognition, and autonomic symptoms.
Serum Tryptase
Mast cell activation marker - elevated in MCAS
Sestamibi scan
A nuclear medicine imaging study that uses a radioactive tracer to locate overactive parathyroid tissue. Used for surgical planning, NOT for diagnosis. A negative scan doesn't mean you don't have PHPT.
SGLT2 inhibitor
A newer class of medications that slows CKD progression and reduces cardiovascular risk, even in many patients without diabetes.
SGLT2i
Sodium-glucose cotransporter 2 inhibitors - diabetes medications that cause glucose excretion in urine. Beyond glucose control, they show cardiovascular and kidney protection. Examples: empagliflozin, dapagliflozin.
SHBG
Sex Hormone Binding Globulin.
SHBG (Sex Hormone Binding Globulin)
High SHBG = less free testosterone available
Shoemaker Protocol
A functional-medicine sequence used by some CIRS clinicians after exposure removal. It isn't established mainstream mold care.
short-chain fatty acid
Metabolites (butyrate, propionate, acetate) produced when gut bacteria ferment fibre. They strengthen the gut lining, reduce systemic inflammation, and directly support neuron health.
SIBO
Small intestinal bacterial overgrowth - bacteria that should live in the large intestine colonize the small intestine, causing bloating, malabsorption, and brain fog via the gut-brain axis.
SIBO Breath Test
Screens for small intestinal bacterial overgrowth
SIFO
of patients with unexplained GI symptoms had small intestinal fungal overgrowth.
sIgA (Secretory IgA)
Gut immune function - low in chronic stress, dysbiosis
SII
Systemic Immune-Inflammation Index - a composite blood marker calculated from CBC that tracks overall immune activation.
SIMO
Small Intestinal Microbial Overgrowth. A newer umbrella term for SIBO that includes bacteria, archaea (methanogens), and other microbes, not just bacteria.
SLEDAI
SLE Disease Activity Index - a standardized scoring system used by rheumatologists to measure lupus disease activity. Higher scores indicate more active disease. Useful for tracking whether treatment is controlling lupus activity over time.
Sleep
Sleep is a nearby overlapping cause that is often worth ruling out when the story pattern is similar.
Sleep Apnea
Obstructive sleep apnea frequently coexists with diabetes and worsens insulin resistance through intermittent hypoxia and sleep fragmentation. Treating sleep apnea can improve HbA1c and cognitive symptoms. Worth investigating if fog is worst on waking with snoring or unrefreshing sleep.
Sleep Latency Testing
Time to fall asleep - <8 min indicates severe sleep deprivation
Sleep Study (PSG)
Overnight polysomnography explainer framed around the patient-facing 'sleep study' language most people actually search.
Small fiber neuropathy
Damage to the small nerve fibers that detect pain and temperature. Can cause burning, tingling, and autonomic symptoms. Has been associated with Bartonella infection in clinical case series.
SMART protocol
A safer-amalgam-removal protocol used by trained biological dentists to reduce mercury vapor exposure during dental drilling.
SNOT-22
Sino-Nasal Outcome Test - a 22-question validated patient-reported outcome measure for CRS symptom severity. Used to track treatment response.
Social isolation
Objective lack of social contact, measured by factors like living alone, few social contacts per week, and limited community participation. Distinct from loneliness, which is subjective. Both independently affect cognition.
Social jetlag
The mismatch between your biological clock and your social schedule, often seen when weekend wake times drift far later than workday wake times.
Social prescribing
A healthcare approach, pioneered by the NHS, where clinicians prescribe community activities (support groups, volunteering, classes, peer connections) alongside or instead of medical treatments for conditions like loneliness and social isolation.
Somatic Experiencing
A body-oriented therapy developed by Peter Levine for resolving trauma held in the body. One RCT (Brom et al. 2017) showed significant benefit for PTSD symptoms.
Somatopause
The age-related decline in growth hormone and IGF-1 signaling that may overlap with reduced recovery capacity, muscle maintenance, and resilience.
Somatotroph Cells
The specific cells in the anterior pituitary that produce growth hormone. These are the cells damaged in GHD.
Somatotropin
Another name for growth hormone. Recombinant somatotropin is the synthetic form used in GH replacement therapy.
SPECT Scan
Brain perfusion imaging - shows hypoperfusion areas
SpO2
Peripheral oxygen saturation - the oxygen reading used on sleep tests and pulse oximetry to show how low breathing events are driving the blood oxygen level.
statin
Cholesterol-lowering medications. Some people report cognitive side effects (memory problems, confusion). Lipophilic statins (atorvastatin, simvastatin) cross the blood-brain barrier more readily than hydrophilic ones.
Stem cell transplant (autologous)
A procedure using high-dose melphalan to kill myeloma cells, followed by infusion of the patient's own stem cells to restore marrow. Cognitive effects can last 3-12 months.
Stimulant medication
First-line ADHD medications such as methylphenidate and amphetamine formulations.
STOP-BANG
A rapid 8-item screening questionnaire for obstructive sleep apnea risk.
STOPP/START
Two prescribing checklists used in older adults: STOPP flags medications that may be inappropriate, and START highlights useful treatments that may have been omitted.
Stress-related exhaustion disorder (SED)
A Swedish diagnostic category (ICD-10-SE F43.8A) that formally recognizes burnout as a clinical condition requiring at least 6 months of identifiable stressors. More specific than the WHO QD85 classification.
Sugar
Sugar is a nearby overlapping cause that is often worth ruling out when the story pattern is similar.
Sugar (Blood Sugar Pattern)
A separate cause page covering brain fog from dietary sugar sensitivity in people with normal glucose labs. The distinction from diabetes is whether there's measurable metabolic dysfunction (diabetes) or purely dietary sensitivity (sugar pattern).
Sulforaphane
A compound concentrated in broccoli sprouts and other cruciferous vegetables that's studied for its role in pollutant detox pathways.
Surgical menopause
Immediate menopause caused by bilateral oophorectomy (surgical removal of ovaries). More abrupt hormone drop than natural menopause. Earlier age at surgery correlates with greater cognitive risk.
SWAN study
Study of Women's Health Across the Nation. Multi-site longitudinal study following women through the menopausal transition. Source of key findings on cognitive changes being transient and recovering postmenopause.
sympathetic
The 'fight-or-flight' branch of the autonomic nervous system. Chronic sympathetic dominance (from ongoing stress) drives cortisol elevation, inflammation, and brain fog.
symptom cluster
A group of symptoms that tend to occur together, identified through clinical pattern recognition or statistical analysis. Cluster language is useful when the same diagnosis can show up in different dominant patterns.
Symptom Tracking (2+ Cycles)
Map fog timing to cycle phases for hormonal patterns
syncope
Fainting or loss of consciousness caused by temporary insufficient blood flow to the brain, often triggered by standing or position change.
tapering
Gradually reducing caffeine intake, typically by 25% every 3-5 days, to minimize withdrawal symptoms rather than stopping cold turkey.
Telepressure
The felt pressure to respond quickly to messages and digital communication, even when the device is technically silent.
Testosterone
Primary male hormone - affects cognition, mood, energy
TGF-beta-1
Transforming Growth Factor Beta-1. An inflammatory marker often elevated in CIRS. Not specific to mold exposure; it rises in many inflammatory states.
TGF-β1
Mold/CIRS marker - elevated in biotoxin illness
theta rhythm
Brain waves in the 4-7 Hz frequency range, associated with drowsiness, cognitive slowing, and reduced information processing efficiency. Elevated theta power in brain fog patients correlates with subjective fatigue severity (Fabio 2024). Think of theta as your brain's 'buffering' indicator - when it's elevated, information processing is sluggish.
thiamine (vitamin B1)
Essential B-vitamin for glucose metabolism in neurons. Depleted by alcohol use. Severe deficiency causes Wernicke's encephalopathy and, if untreated, permanent Korsakoff's syndrome.
Thyroglobulin Antibodies
Second marker for autoimmune thyroid disease
Thyroid
Thyroid is a nearby overlapping cause that's often worth ruling out when the story pattern is similar.
TIBC
Total iron-binding capacity - measures how much iron your blood can carry. High TIBC with low ferritin confirms iron deficiency, even when haemoglobin looks normal.
tilt table test
The gold standard diagnostic test for POTS.
Time blindness
Difficulty sensing how long tasks take, how much time has passed, or how close a deadline really is.
Timing hypothesis
The concept that HRT started within 10 years of menopause (or before age 60) may protect cognition, while starting later shows no benefit or possible harm. Supported by Song et al. 2025 meta-analysis.
TNF
Tumour necrosis factor-alpha - a pro-inflammatory cytokine. Elevated in chronic inflammation, obesity, and autoimmune disease. Impairs synaptic plasticity (the brain's ability to form new connections).
TNF-α (Tumor Necrosis Factor Alpha)
Key inflammatory cytokine - elevated crosses blood-brain barrier
tolerance
The body's adaptation to chronic caffeine use through adenosine receptor upregulation, requiring increasing doses for the same effect and causing withdrawal when stopped.
Total + Free Testosterone
This panel should be used selectively.
Total Testosterone
Low T impairs verbal memory and processing speed
tPBM
Transcranial photobiomodulation: red or near-infrared light delivered to the head to target brain tissue rather than skin or muscle.
TPO
Thyroid peroxidase antibodies - elevated levels indicate Hashimoto's thyroiditis (autoimmune thyroid disease), one of the most commonly missed causes of brain fog.
TPO Antibodies
Elevated in Hashimoto's thyroiditis - autoimmune thyroid attack
transcranial
Delivered through the skull to the brain - refers to non-invasive therapies like transcranial photobiomodulation (light) or transcranial direct current stimulation (electrical) that target brain tissue from outside.
Transcranial Doppler
Measures cerebral blood flow - detects hypoperfusion
transferrin saturation
Percentage of the iron-transport protein transferrin that's loaded with iron. Below 20% suggests functional iron deficiency.
Trauma
Trauma-related brain fog refers to cognitive impairment driven by a nervous system stuck in survival mode, often presenting as dissociation, shutdown, hypervigilance, or difficulty accessing memory and attention.
Trio-Smart (3-Gas Breath Test)
Advanced at-home breath test measuring hydrogen, methane, AND hydrogen sulfide to distinguish SIBO, IMO, and ISO subtypes.
triptan
A class of medications (sumatriptan, rizatriptan, etc.) that target serotonin receptors specifically involved in migraine. First-line acute treatment. Most effective when taken early in an attack.
tryptase
A protease enzyme released by mast cells during degranulation. Serum tryptase is the most commonly ordered MCAS biomarker, but it's often normal between flares and must be collected during symptoms for diagnostic value.
TSH
Thyroid-stimulating hormone - the standard thyroid screening test.
TSH (Thyroid Stimulating Hormone)
Primary thyroid screening marker.
TSH + B12 + Ferritin
This grouped panel is useful when the story could reflect thyroid slowdown, iron depletion, or B12-related cognitive symptoms and you want one first-pass conversation instead of three disconnected requests.
TSH + Free T3 + Free T4
This panel helps frame whether the story fits thyroid slowdown, conversion issues, or a closer competitor cause before you default to broad lifestyle explanations.
tTG-IgA (Celiac)
Patient-facing celiac serology explainer route focused on the test wording users actually bring from clinician visits.
tTG-IgA (Tissue Transglutaminase)
Celiac disease screening - gluten triggers neuroinflammation
turbinate
Bony structures inside the nose covered with mucosa that warm, humidify, and filter air. Enlarged turbinates cause nasal obstruction.
Tyrosine
An amino acid used as a precursor in catecholamine synthesis. It's one reason protein is discussed in the ADHD food section.
UACR
Urine albumin-to-creatinine ratio - the standard screening test for albuminuria.
UARS
Upper Airway Resistance Syndrome, a sleep-related breathing problem that can mimic ADHD-like fatigue and brain fog.
UARS/RERA Scoring
Detects subtle upper airway resistance missed by standard AHI
UCLA Loneliness Scale
A 20-item validated questionnaire measuring perceived loneliness. Scores range from 20-80, with higher scores indicating greater loneliness. A 3-item short form exists for screening. More informative than blood tests for assessing social isolation.
Ulcerative Colitis (UC)
A type of IBD limited to the colon and rectum. UC's brain fog is more purely inflammation-driven, with fMRI showing decreased hippocampal activity.
Upright MRI
Detects cervical instability missed by supine MRI
Uremic toxins
Waste products such as indoxyl sulfate and p-cresyl sulfate that accumulate when kidney function falls and can contribute to neuroinflammation and cognitive dysfunction.
Urine Mercury
Longer-term mercury exposure marker
Urine Mycotoxin Panel
Tests for mold toxin metabolites in urine.
Urine Organic Acids Test
Detects metabolic dysfunction, mitochondrial issues, and fungal metabolites.
UVB
Ultraviolet B radiation (290-315 nm wavelength) from sunlight. Triggers vitamin D3 synthesis in skin. Blocked by glass, sunscreen, and cloud cover. Strongest at midday and lower latitudes.
vagal
Relating to the vagus nerve - the main nerve of the parasympathetic nervous system. Vagal tone refers to the activity level of this nerve. Higher vagal tone = better stress resilience and lower inflammation.
Vagal Tone
A measure of vagus nerve activity reflecting the capacity for nervous system regulation. Low vagal tone is associated with difficulty calming down after stress, poor emotional regulation, and persistent cognitive fog.
vagus nerve
The longest cranial nerve, connecting the brain to the gut, heart, and lungs. It controls the parasympathetic (rest-and-digest) nervous system. Stimulating it (cold exposure, deep breathing, gargling) reduces inflammation.
valacyclovir
An antiviral medication sometimes used off-label for chronic EBV reactivation. Evidence is limited (one small open-label study). Usually reserved for clear reactivation with elevated EA.
varenicline
A prescription smoking cessation medication (brand names Chantix/Champix) that partially stimulates nicotinic acetylcholine receptors, reducing cravings and withdrawal severity.
Vasculitis
Inflammation of blood vessels. Bartonella specifically invades endothelial cells lining blood vessels, causing vasculitis that can lead to visible skin changes (shin streaks) and circulation problems.
Vasomotor symptoms
Hot flashes and night sweats caused by disrupted thermoregulation as estrogen declines. Night sweats fragment sleep, which is the primary driver of menopause-related brain fog.
VCA
Viral Capsid Antigen - an EBV protein. VCA IgM indicates recent infection; VCA IgG indicates past exposure (positive in 90% of adults).
VCS
Visual Contrast Sensitivity. A quick screening test measuring ability to detect faint contrast patterns. Used in some CIRS protocols as a non-specific marker that can change with many conditions, not just mold.
VCS Test (Visual Contrast Sensitivity)
Free screening for mold/CIRS - reduced contrast sensitivity
VEGF
Vascular Endothelial Growth Factor.
VEGF (Vascular Endothelial Growth Factor)
Growth factor that regulates blood vessel formation and oxygen delivery.
vestibular
Relating to the inner ear balance system. Vestibular dysfunction is common after concussion and treatable with vestibular rehabilitation.
Vestibular Assessment
Tests balance system - dysfunction causes dizziness, fog
vestibular migraine
A migraine variant where dizziness, balance problems, and cognitive fog dominate, often with minimal or no headache. One of the most underdiagnosed causes of episodic cognitive dysfunction.
VIP
Vasoactive intestinal peptide - a neuropeptide with anti-inflammatory and regulatory functions. Used as a nasal spray in some CIRS protocols for patients who don't fully respond to other treatments. Requires prescription and monitoring.
VIP nasal spray
A later-step treatment in some Shoemaker-style protocols. It is specialty care, not standard mainstream mold treatment.
Vitamin B12
Patient-facing vitamin B12 explainer route, useful when a story or clinician uses plain language instead of the active-B12 variant.
Vitamin D
Vitamin D can contribute to brain fog.
Vitamin D (25-OH)
Patient-facing vitamin D explainer route matching the common 25-OH wording used in lab and search language.
VOC
Volatile organic compound - gases released from fragrances, cleaners, renovation materials, furniture, and many household products.
VOMS
Vestibular Ocular Motor Screening - tests smooth pursuit, saccades, VOR, convergence, and visual motion sensitivity to identify vestibular involvement after concussion.
Vortioxetine
An antidepressant (brand name Trintellix) with specific evidence for improving cognitive function in depression, independent of mood effects.
Welchol
Brand name for colesevelam, a gentler bile-acid sequestrant that some mold-focused clinicians use when cholestyramine is poorly tolerated.
Wernicke Encephalopathy
Acute neurological emergency caused by severe thiamine (B1) deficiency. Classic triad: confusion, eye movement abnormalities (ophthalmoplegia), and balance problems (ataxia). Treatable with IV thiamine but can cause permanent brain damage if missed.
Wernicke-Korsakoff syndrome
Two-stage neurological disorder from thiamine deficiency, most common in heavy alcohol use. Wernicke's phase: acute confusion, eye movement problems, balance loss. Korsakoff's phase: permanent short-term memory impairment. A medical emergency requiring immediate thiamine treatment.
Western Blot (Lyme)
Lyme confirmatory test - follows positive ELISA
Window of Tolerance
The zone of nervous system arousal where a person can function effectively. Too high (hyperarousal) or too low (hypoarousal) and cognitive function degrades. Trauma narrows this window.
withdrawal
A set of symptoms (headache, fatigue, fog, irritability, flu-like feelings) that occur 12-24 hours after the last caffeine dose, peaking at days 2-3. Recognized as DSM-5 diagnosis 292.0.
Working memory
The ability to hold information in mind long enough to use it. In ADHD this often feels brittle or inconsistent.
WURS
The Wender Utah Rating Scale, often used to help reconstruct childhood ADHD symptoms.
Yoga Nidra
A guided resting meditation sometimes used as an NSDR-style practice to reduce arousal and support recovery.
zonulin
A protein that regulates the tight junctions between gut lining cells. Gluten and certain bacteria trigger zonulin release, opening gaps in the gut wall (intestinal permeability) and allowing inflammatory molecules into the bloodstream.
Note on Clinical Language
The Field Guide uses precise medical terminology to ensure accuracy. If you encounter a term not listed here, please check our editorial methodology or consult your healthcare provider for clarification.
Definitions here are simplified for accessibility. For cited clinical detail, open the corresponding cause page, article, or test explainer rather than treating the glossary as the final source.
Related Causes
Glossary readers often need direct examples tied to technical terms.