Brain Injury Glossary: Clear Definitions of Common Neurological Terms
Brain Injury Glossary
Medical appointments move fast and the terminology rarely gets explained. This glossary covers the neurological terms that come up most often for families navigating brain injury, CTE, dementia, Parkinson's, PTSD, FND, and related conditions. Each term includes a clinical definition, a plain-language explanation, and why it matters for caregivers.
This glossary supports the Brain Injury 101 educational library. Where a full article exists, a link is provided.
Akinesia
Medical Definition
Absence or marked reduction of voluntary movement, commonly associated with Parkinson's disease and other movement disorders.
Plain Language
The brain sends the signal to move but the body does not respond normally. Movement may freeze or fail to initiate.
Why This Matters
Akinesia affects daily tasks, safety, and independence. It is distinct from weakness and requires different management strategies.
Amygdala
Medical Definition
Structure deep within the brain involved in emotional processing, fear response, and threat detection.
Plain Language
Part of the brain's alarm system.
Why This Matters
Changes in amygdala function may affect emotional reactions, stress responses, and how the person responds to perceived threats.
Anosognosia
Medical Definition
Neurological condition in which a person lacks awareness of their own impairment due to dysfunction in brain regions responsible for self-awareness.
Plain Language
The brain cannot recognize that it is injured. This is not denial. It is a symptom.
Why This Matters
Affects treatment decisions, safety awareness, and the ability to agree to help. Understanding anosognosia helps caregivers respond with accuracy rather than frustration.
Anterior Cingulate Cortex
Medical Definition
Brain region involved in emotional regulation, attention, decision-making, and error detection.
Plain Language
Helps manage emotions, focus, and self-monitoring.
Why This Matters
Disruption in this region can affect emotional control and the ability to self-correct behavior.
Aphasia
Medical Definition
Language disorder caused by neurological damage affecting the ability to speak, understand speech, read, or write. Does not affect intelligence.
Plain Language
The words are in there but the brain has trouble getting them out or understanding them coming in. Thinking is intact even when language is not.
Why This Matters
Aphasia is frequently misread as confusion or cognitive decline. Understanding aphasia changes how caregivers and providers communicate with the person.
Atypical Parkinsonism
Medical Definition
Group of neurological disorders that produce movement symptoms similar to Parkinson's disease but follow different progression patterns and respond differently to treatment.
Plain Language
Movement symptoms that look like Parkinson's but have a different underlying cause and often a different trajectory.
Why This Matters
Treatments that help Parkinson's disease may not work the same way for atypical Parkinsonism. Accurate diagnosis affects the entire care plan.
Autonomic Dysfunction
Medical Definition
Impaired regulation of involuntary body functions including heart rate, blood pressure, digestion, and temperature control.
Plain Language
The body's automatic systems stop regulating normally. This can cause dizziness when standing, digestive problems, and difficulty with temperature.
Why This Matters
Autonomic dysfunction can cause falls, fainting, and serious complications that may appear unrelated to brain injury but are directly connected.
Brain Fog
Medical Definition
Subjective cognitive symptoms including slowed thinking, reduced mental clarity, difficulty concentrating, and impaired word retrieval.
Plain Language
Thinking feels cloudy, slow, or like pushing through mud. Common after brain injury, illness, or during neurological flares.
Why This Matters
Brain fog affects work, memory, and daily functioning. It is a real neurological symptom, not laziness or lack of effort.
Caregiver Burden
Medical Definition
Documented physical, emotional, financial, and social strain experienced by individuals providing ongoing care for someone with chronic illness or neurological injury.
Plain Language
The cumulative weight of caregiving. Not a personal failing. A clinical reality with measurable health consequences for caregivers.
Why This Matters
Caregiver burden increases the risk of depression, physical illness, and burnout. Recognizing it is the first step toward addressing it.
Chronic Traumatic Encephalopathy (CTE)
Medical Definition
Progressive neurodegenerative condition associated with repeated head impacts and abnormal accumulation of tau protein in specific patterns throughout the brain. Currently diagnosed only at autopsy.
Plain Language
Brain condition linked to repeated hits to the head over time. Cannot be definitively confirmed while the person is alive.
Why This Matters
CTE affects mood, behavior, cognition, and movement in ways that overlap with other conditions. Understanding CTE helps families recognize patterns that may otherwise be misattributed.
Cognitive Decline
Medical Definition
Gradual reduction in cognitive abilities including memory, reasoning, attention, language, and executive function.
Plain Language
Thinking abilities that were once reliable become less consistent over time.
Why This Matters
Early recognition allows for earlier intervention, planning, and safety measures.
Cognitive Fatigue
Medical Definition
Mental exhaustion resulting from the increased neurological effort required for cognitive tasks after brain injury or neurological disease.
Plain Language
The brain is working harder than it used to for the same tasks. That extra effort depletes mental energy faster than it used to.
Why This Matters
Cognitive fatigue is not visible and is frequently underestimated. Pushing through it makes symptoms worse. Pacing is a legitimate medical strategy.
Cognitive Overload
Medical Definition
State in which incoming information or environmental demands exceed the brain's reduced processing capacity, causing system breakdown in thinking, behavior, or emotional regulation.
Plain Language
Too much coming in at once. The brain cannot sort and process it all and begins to shut down or dysregulate.
Why This Matters
Understanding cognitive overload helps caregivers reduce environmental triggers before a breakdown occurs rather than managing the aftermath.
Complex PTSD (cPTSD)
Medical Definition
Post-traumatic stress condition resulting from prolonged, repeated trauma rather than a single event. Includes core PTSD symptoms plus significant disturbances in self-perception, emotional regulation, and relationships.
Plain Language
PTSD that developed from sustained trauma over time rather than one incident. The effects run deeper and are often more complex to treat.
Why This Matters
cPTSD is common in combat veterans and significantly overlaps with TBI and CTE in terms of behavioral and emotional presentation. Distinguishing between them affects treatment.
Corticobasal Degeneration
Medical Definition
Rare progressive neurodegenerative disorder affecting the cerebral cortex and basal ganglia, producing asymmetric movement problems alongside cognitive and language changes.
Plain Language
A condition that affects both movement and thinking, often affecting one side of the body more than the other.
Why This Matters
Sometimes misdiagnosed as Parkinson's disease. Understanding the distinction helps families advocate for accurate diagnosis and appropriate care.
Decision Fatigue
Medical Definition
Deterioration in the quality of decisions made after prolonged cognitive effort or repeated decision-making demands.
Plain Language
The brain runs out of decision-making capacity. Later decisions in a day tend to be worse than earlier ones.
Why This Matters
Scheduling important conversations and decisions earlier in the day, when cognitive resources are highest, produces better outcomes.
Dementia
Medical Definition
Umbrella term for a group of symptoms affecting memory, thinking, and social abilities severely enough to interfere with daily functioning. Caused by various underlying neurological conditions.
Plain Language
Not a single disease but a description of symptoms. Alzheimer's is one cause of dementia. So are Lewy body disease, vascular damage, CTE, and Parkinson's disease.
Why This Matters
The underlying cause of dementia determines the treatment approach, progression pattern, and what caregivers can expect over time.
Disinhibition
Medical Definition
Reduced ability to suppress impulsive thoughts, words, or behaviors due to frontal lobe disruption.
Plain Language
The brain's filter stops working reliably. Things that would normally be held back come out instead.
Why This Matters
Disinhibition is a neurological symptom, not a character change. Understanding this protects the relationship between the caregiver and the person they care for.
Dysarthria
Medical Definition
Motor speech disorder caused by weakness, paralysis, or incoordination of the muscles used for speaking. Affects clarity and volume of speech.
Plain Language
The mechanics of speaking are affected. Words may be slurred, slow, or quiet even when the person knows exactly what they want to say.
Why This Matters
Dysarthria is often confused with cognitive impairment. Clear speech and clear thinking are separate systems. A person can have significant dysarthria and intact cognition.
Dysphagia
Medical Definition
Difficulty swallowing caused by neurological impairment affecting the coordination of muscles involved in swallowing.
Plain Language
Swallowing becomes difficult or unsafe. Food or liquid may go into the airway instead of the esophagus.
Why This Matters
Dysphagia increases the risk of aspiration pneumonia, a serious and potentially life-threatening complication. It requires evaluation by a speech-language pathologist.
Emotional Dysregulation
Medical Definition
Difficulty managing emotional responses proportionately to the situation, caused by neurological changes affecting the brain's emotional regulation systems.
Plain Language
Emotions come on faster, harder, or less predictably than before. The response may not match the situation from the outside but is neurologically real.
Why This Matters
Emotional dysregulation is one of the most challenging symptoms for families to navigate because it affects the relationship directly. It is a symptom, not a choice.
Emotional Blunting
Medical Definition
Reduced intensity or range of emotional response following neurological injury or disease. The person may feel less reactive to both positive and negative events.
Plain Language
Emotions feel flatter or less accessible. This is not the same as not caring. The neurological connection between feeling and expressing emotion has been disrupted.
Why This Matters
Emotional blunting is frequently misread by families as indifference or depression. Understanding the neurological basis helps caregivers avoid personalizing it.
Energy Envelope Theory
Medical Definition
Framework describing how individuals with neurological conditions function best when activity levels stay within their available cognitive and physical energy limits.
Plain Language
Everyone has a daily energy budget. After brain injury that budget is smaller and harder to predict. Staying within it reduces crashes and symptom flares.
Why This Matters
Pacing is not giving up. It is a documented management strategy that reduces the severity and frequency of symptom flares.
Executive Dysfunction
Medical Definition
Impairment in the set of cognitive skills governing planning, organization, task initiation, sequencing, task completion, working memory, and flexible thinking. Managed primarily by the prefrontal cortex.
Plain Language
The brain has trouble starting tasks, staying on them, switching between them, or finishing them. The ability to plan ahead and follow through is affected.
Why This Matters
Executive dysfunction affects nearly every area of daily life. It is one of the most common and most misunderstood effects of TBI, dementia, CTE, and Parkinson's disease.
Frontotemporal Dementia (FTD)
Medical Definition
Group of neurodegenerative conditions primarily affecting the frontal and temporal lobes of the brain, producing changes in personality, behavior, language, and judgment before memory is significantly affected.
Plain Language
A type of dementia that often shows up first as personality changes, impulsivity, or language problems rather than memory loss.
Why This Matters
FTD is frequently misdiagnosed as psychiatric illness because memory may be relatively preserved early on. The behavioral symptoms can be severe and are neurological in origin.
Functional Neurological Disorder (FND)
Medical Definition
Neurological condition involving disrupted brain network function producing genuine physical and neurological symptoms without structural damage visible on standard imaging.
Plain Language
The brain is sending the wrong signals. Symptoms are real and can be severe and disabling even when scans look normal. This is a software problem, not a hardware problem.
Why This Matters
FND carries significant stigma and is frequently dismissed by clinicians. Average time to correct diagnosis is 8.4 years. Understanding FND helps families advocate effectively and respond to symptoms accurately.
Hypomimia
Medical Definition
Reduced facial expression caused by neurological impairment of the muscles controlling facial movement, commonly associated with Parkinson's disease.
Plain Language
The face appears flat or expressionless even when the person is engaged, happy, or emotionally present. Sometimes called facial masking.
Why This Matters
Hypomimia is frequently misread as depression, disengagement, or cognitive decline. The person may be fully present and emotionally connected even when their face does not show it.
Impulse Control
Medical Definition
Cognitive ability to pause, evaluate, and inhibit impulsive responses before acting or speaking. Governed primarily by the prefrontal cortex and disrupted by frontal lobe damage.
Plain Language
The ability to stop before doing or saying something. When this is impaired, responses come out before the filter has a chance to engage.
Why This Matters
Impulse control disorders are documented in dementia, CTE, TBI, and Parkinson's disease. Impulsive purchasing, risky decisions, and disinhibited speech are neurological symptoms, not character flaws.
Irritability
Medical Definition
Increased neurological sensitivity to frustration, noise, demands, and stress resulting in lower threshold for anger or agitation following brain injury or neurological disease.
Plain Language
The fuse is shorter. Things that would not have triggered a reaction before now do. The neurological tolerance for stress has been reduced.
Why This Matters
Irritability is one of the most relationship-straining symptoms of brain injury. Understanding the neurological basis protects caregivers from personalizing responses that are driven by the injury, not the person.
Lewy Body Dementia
Medical Definition
Neurodegenerative disorder caused by abnormal deposits of alpha-synuclein protein in brain cells, affecting cognition, behavior, movement, and autonomic function.
Plain Language
A type of dementia that often includes visual hallucinations, movement symptoms similar to Parkinson's, and significant fluctuations in alertness and cognition.
Why This Matters
Some medications commonly used for other dementias can cause severe reactions in people with Lewy body dementia. Accurate diagnosis is critical for safe treatment.
Memory Impairment
Medical Definition
Reduced ability to encode, store, or retrieve information due to neurological damage or disease. May affect short-term memory, long-term memory, or both depending on the location and nature of the injury.
Plain Language
Forgetting happens more and recovery of information is less reliable. Not all forgetting is equal. Different types of memory are affected differently.
Why This Matters
Understanding which type of memory is affected helps caregivers communicate more effectively and set realistic expectations.
Mild Cognitive Impairment (MCI)
Medical Definition
Stage between normal age-related cognitive changes and dementia, characterized by noticeable cognitive decline that does not yet significantly interfere with daily functioning.
Plain Language
Thinking and memory are measurably below where they used to be but the person can still manage most daily activities independently.
Why This Matters
MCI does not always progress to dementia but it is a significant risk factor. Early recognition allows for planning, legal preparation, and lifestyle interventions that may slow progression.
Mild Traumatic Brain Injury (mTBI)
Medical Definition
Brain injury classification that includes concussion. Characterized by brief loss of consciousness or alteration of consciousness, confusion, and neurological symptoms. The word mild refers to injury severity at the time of impact, not the duration or severity of symptoms.
Plain Language
Concussion is mTBI. Mild does not mean insignificant. Symptoms can persist for months or years and repeated mTBIs compound in effect.
Why This Matters
The term mild frequently causes families and clinicians to underestimate the impact. Repeated mild TBIs are associated with CTE and long-term cognitive decline.
Neurodegeneration
Medical Definition
Progressive loss of structure or function of neurons, including their death, over time. The underlying mechanism in Alzheimer's, Parkinson's, CTE, and other neurodegenerative diseases.
Plain Language
Brain cells are progressively lost or damaged over time. This is the process underlying conditions like CTE, Parkinson's disease, and Alzheimer's.
Why This Matters
Understanding that neurodegeneration is progressive helps families plan ahead and prioritize what matters most at each stage.
Neuroinflammation
Medical Definition
Inflammatory response occurring within the brain and nervous system following injury, infection, or disease. Can contribute to ongoing neurological damage beyond the initial injury.
Plain Language
The brain's immune response can cause additional damage after the original injury. Inflammation that helps elsewhere in the body can be harmful when it persists in the brain.
Why This Matters
Neuroinflammation is a key mechanism in CTE progression and is an active area of research for potential treatment targets.
Neuroplasticity
Medical Definition
The brain's ability to reorganize itself by forming new neural connections in response to learning, experience, or injury.
Plain Language
The brain can rewire itself. This is the foundation of rehabilitation after brain injury.
Why This Matters
Neuroplasticity means recovery and adaptation are possible even after significant brain injury. It also means that consistent therapy and cognitive engagement have real neurological effects.
Parkinson's Disease
Medical Definition
Progressive neurodegenerative disorder caused by loss of dopamine-producing neurons in the substantia nigra, producing motor symptoms and non-motor symptoms including cognitive changes, mood disorders, and autonomic dysfunction.
Plain Language
A brain condition affecting movement, thinking, mood, and many automatic body functions. Far more than a tremor disorder.
Why This Matters
Parkinson's disease is significantly underestimated by families and sometimes by clinicians. Non-motor symptoms including cognitive decline, depression, and autonomic dysfunction often cause more disability than the movement symptoms.
Parkinsonism
Medical Definition
Umbrella term for movement symptoms including tremor, rigidity, slowed movement, and postural instability that can occur in Parkinson's disease and other neurological conditions.
Plain Language
Movement symptoms that look like Parkinson's disease but may have a different underlying cause.
Why This Matters
Not all Parkinsonism is Parkinson's disease. The distinction matters for treatment decisions and prognosis.
Post-Concussive Syndrome
Medical Definition
Persistent neurological, cognitive, and emotional symptoms lasting weeks, months, or longer after concussion or mild TBI.
Plain Language
Concussion symptoms that do not resolve on the expected timeline. Headaches, brain fog, mood changes, and sleep disruption that continue beyond the acute phase.
Why This Matters
Post-concussive syndrome is common and frequently undertreated. It can significantly affect work, relationships, and quality of life.
Prefrontal Cortex
Medical Definition
Front region of the brain's frontal lobe responsible for executive functions including decision-making, impulse control, working memory, planning, and social behavior.
Plain Language
The brain's control center for judgment and self-regulation. Damage here affects behavior, decision-making, and emotional control.
Why This Matters
The prefrontal cortex is highly vulnerable to TBI and is significantly affected in CTE. Many of the behavioral changes families find most difficult to navigate originate here.
Processing Speed
Medical Definition
Rate at which the brain takes in, interprets, and responds to information. Commonly reduced after brain injury, neurological disease, and aging.
Plain Language
Everything takes longer to process. The information gets there but slower than it used to.
Why This Matters
Slowed processing speed affects conversations, decision-making, driving, and workplace performance. Giving more time and fewer simultaneous demands helps significantly.
PTSD (Post-Traumatic Stress Disorder)
Medical Definition
Psychiatric condition that develops following exposure to traumatic events, characterized by intrusive symptoms, avoidance, negative alterations in cognition and mood, and hyperarousal.
Plain Language
The nervous system gets stuck in threat response mode after trauma. The brain and body respond to current situations as if the original threat is still present.
Why This Matters
PTSD in veterans frequently co-occurs with TBI and significantly overlaps with CTE in presentation. The conditions interact and compound each other in ways that require coordinated care.
Reduced Stress Tolerance
Medical Definition
Lowered neurological threshold for managing cognitive, emotional, or sensory demands following brain injury or neurological disease.
Plain Language
The brain has less capacity to handle stress than it used to. What was manageable before may now trigger significant symptom flares.
Why This Matters
Reducing unnecessary stressors in the environment is a legitimate medical intervention, not over-accommodation.
Repetitive Head Impacts
Medical Definition
Multiple blows or jolts to the head sustained over time, whether in sport, military service, or other contexts. Associated with cumulative neurological damage and CTE development.
Plain Language
The cumulative effect of repeated hits to the head over a lifetime. Each impact may seem minor but the total is not.
Why This Matters
Understanding the cumulative nature of head impacts helps explain why symptoms may appear years or decades after the exposures that caused them.
Sensory Overload
Medical Definition
State in which incoming sensory stimulation exceeds the brain's reduced capacity to filter and process it, causing cognitive, behavioral, or physical breakdown.
Plain Language
Too much sensory input at once. Noise, light, activity, and crowd density that others manage normally can overwhelm a brain that is already working at reduced capacity.
Why This Matters
Sensory overload is a neurological event, not a behavioral choice. Reducing sensory input before the threshold is reached prevents the event rather than managing the aftermath.
Sensory Sensitivity
Medical Definition
Heightened neurological response to sensory input including light, sound, touch, and smell, commonly occurring after TBI and in other neurological conditions.
Plain Language
The brain amplifies sensory input. Things that are mildly annoying to others can be genuinely painful or overwhelming.
Why This Matters
Sensory sensitivity is invisible to everyone else and frequently dismissed. It significantly affects where a person can go and what environments they can tolerate.
Social Masking
Medical Definition
Cognitive and behavioral effort used to conceal neurological symptoms in social settings, often resulting in significant post-interaction fatigue.
Plain Language
Performing normally in public takes enormous effort and depletes the energy needed for everything else. The crash that follows a social event is real and predictable.
Why This Matters
People who appear fine in social settings may be significantly impaired at home afterward. What others see is the performance. What caregivers see is the real picture.
Subconcussive Impacts
Medical Definition
Head impacts that do not cause overt concussion symptoms at the time but may cause measurable neurological changes with cumulative exposure. Associated with CTE development in contact sport athletes and military personnel.
Plain Language
Hits to the head that don't feel like a big deal in the moment but add up over time.
Why This Matters
Subconcussive impacts are believed to be a significant contributor to CTE, independent of diagnosed concussions. Total exposure matters, not just diagnosable events.
Tau Protein
Medical Definition
Protein that normally stabilizes the internal structure of neurons. In certain neurodegenerative conditions including CTE and Alzheimer's disease, tau becomes abnormally modified and accumulates in toxic deposits.
Plain Language
A protein that should help brain cells function normally but in some conditions clumps together and damages the cells instead.
Why This Matters
Tau accumulation is the defining pathological feature of CTE. Research into tau is central to developing diagnostic tools and potential treatments.
Tauopathy
Medical Definition
Group of neurodegenerative diseases defined by the pathological accumulation of abnormal tau protein in the brain, including CTE, Alzheimer's disease, and several other conditions.
Plain Language
A category of brain diseases that share the feature of abnormal tau protein buildup.
Why This Matters
Understanding that CTE is a tauopathy helps families understand why research into CTE is also relevant to Alzheimer's and other conditions.
Traumatic Brain Injury (TBI)
Medical Definition
Disruption of normal brain function caused by a bump, blow, jolt, or penetrating injury to the head. Classified as mild, moderate, or severe based on initial presentation.
Plain Language
Any injury to the brain caused by external force. Ranges from concussion to severe injury with extended loss of consciousness.
Why This Matters
TBI is not one thing. The type, severity, location, and number of injuries all affect outcomes. Repeated TBIs compound in effect even when individual injuries seem minor.
Working Memory
Medical Definition
Cognitive system that temporarily holds and manipulates information needed for ongoing tasks. Distinct from long-term memory and frequently impaired after brain injury.
Plain Language
The mental workspace used to hold information while doing something with it. Walking into a room and forgetting why is a working memory failure.
Why This Matters
Working memory impairment affects conversations, task completion, and the ability to follow multi-step instructions. Shorter, simpler instructions help.
This glossary is maintained by Robbins Nest Alliance, a 501(c)(3) nonprofit. Content is for educational purposes only and does not constitute medical advice. For clinical questions, consult a qualified medical professional. Return to Brain Injury 101 →