Glossary
Plain-language definitions of 73 words you may hear from doctors and researchers.
A
- Acetylcholine
- A chemical messenger in the brain that is important for memory and learning. Levels drop in Alzheimer's disease. Read more
- Activities of daily living (ADLs)
- Basic self-care tasks such as bathing, dressing, eating, toileting and moving around. Doctors use them to judge how much help someone needs.
- Advance directive
- A legal document that records a person's wishes for medical care if they can no longer speak for themselves.
- Agitation
- Restlessness, pacing, irritability or upset behavior, common in middle and later stages of dementia.
- Alzheimer's disease
- A progressive brain disease and the most common cause of dementia, marked by amyloid plaques and tau tangles. Read more
- Amyloid
- A protein fragment (beta-amyloid) that can clump into plaques between brain cells; a hallmark of Alzheimer's. Read more
- Amyloid PET scan
- A brain scan that uses a tracer to show whether amyloid plaques are present. Read more
- Anosognosia
- A brain-based lack of awareness of one's own illness or memory problems. It is not the same as denial.
- Anti-amyloid therapy
- Antibody medicines, such as lecanemab and donanemab, that remove amyloid from the brain to slow early Alzheimer's. Read more
- Aphasia
- Difficulty speaking, finding words, or understanding language, caused by brain damage.
- APOE4
- A common version of the APOE gene that raises the risk of Alzheimer's disease but does not guarantee it. Read more
- Apraxia
- Trouble carrying out learned movements, such as using a fork or getting dressed, even though muscles work.
- ARIA
- Amyloid-related imaging abnormalities: brain swelling or small bleeds seen on MRI, a side effect of anti-amyloid drugs. Read more
- Atrophy
- Shrinking of brain tissue as brain cells are lost.
B
- Biomarker
- A measurable sign of a disease, such as amyloid in blood, spinal fluid or on a scan. Read more
- Blood-brain barrier
- A protective lining of blood vessels that controls what passes from the blood into the brain.
C
- Care plan
- A written plan describing a person's needs, care tasks and who will help. Read more
- Caregiver burnout
- Physical, emotional and mental exhaustion from long-term caregiving. Read more
- Cerebrospinal fluid (CSF)
- The clear fluid around the brain and spinal cord; it can be tested for Alzheimer's proteins. Read more
- Cholinesterase inhibitor
- A class of medicines (donepezil, rivastigmine, galantamine) that boost acetylcholine to help symptoms. Read more
- Clinical trial
- A research study that tests whether a treatment or approach is safe and works in people. Read more
- Cognition
- Thinking skills, including memory, attention, language, reasoning and judgment. Read more
- Cognitive reserve
- The brain's resilience—its ability to keep working well despite damage—built through education and mental activity. Read more
- Cognitive Stimulation Therapy
- A group program of themed activities shown to help thinking and quality of life in mild to moderate dementia. Read more
- Consolidation
- The process by which a new memory becomes stable and long-lasting, much of it during sleep. Read more
- Creutzfeldt-Jakob disease (CJD)
- A rare, rapidly progressing brain disease caused by misfolded proteins called prions.
D
- Delirium
- A sudden, usually temporary state of confusion often caused by illness, infection or medication. It is a medical emergency. Read more
- Dementia
- An umbrella term for a decline in memory and thinking severe enough to interfere with daily life. Read more
- Donanemab
- An anti-amyloid antibody medicine (brand name Kisunla) approved in 2024 for early Alzheimer's. Read more
- Donepezil
- A cholinesterase inhibitor (brand name Aricept) used for all stages of Alzheimer's. Read more
- Durable power of attorney
- A legal document naming someone to make financial or health decisions if you cannot.
E
- Episodic memory
- Memory for personal experiences and events—what happened, where and when. Read more
- Executive function
- Mental skills for planning, organizing, decision-making and switching between tasks.
F
- Frontotemporal dementia (FTD)
- A group of dementias affecting the front and side lobes of the brain, often changing behavior or language first. Read more
G
- Galantamine
- A cholinesterase inhibitor used for mild to moderate Alzheimer's. Read more
- Geriatrician
- A doctor who specializes in the care of older adults.
H
- Hippocampus
- A seahorse-shaped brain region essential for forming new memories; often affected early in Alzheimer's. Read more
- Hospice
- Comfort-focused care for people near the end of life, including those with advanced dementia.
I
- Implicit memory
- Memory you use without conscious effort, such as riding a bike. Read more
- Instrumental activities of daily living (IADLs)
- More complex tasks like managing money, cooking, shopping and taking medicines.
L
- Lecanemab
- An anti-amyloid antibody medicine (brand name Leqembi) approved for early Alzheimer's. Read more
- Lewy bodies
- Abnormal clumps of the protein alpha-synuclein inside brain cells, found in Lewy body dementia and Parkinson's. Read more
- Lewy body dementia
- A dementia with fluctuating alertness, visual hallucinations, movement problems and sleep disturbances. Read more
- Long-term memory
- Memory stored for hours to a lifetime. Read more
M
- Memantine
- A medicine (brand name Namenda) for moderate to severe Alzheimer's that regulates the brain chemical glutamate.
- Memory care
- Specialized residential care designed for people living with dementia. Read more
- Mild cognitive impairment (MCI)
- Noticeable memory or thinking problems that are greater than normal aging but don't stop a person living independently. Read more
- MIND diet
- A brain-healthy eating pattern combining Mediterranean and DASH diets, emphasizing leafy greens, berries, nuts and fish. Read more
- Mini-Mental State Exam (MMSE)
- A short paper-and-pencil test of thinking skills used for screening. Read more
- Mixed dementia
- Dementia caused by more than one condition at once, most often Alzheimer's plus vascular changes.
- Montreal Cognitive Assessment (MoCA)
- A 10-minute screening test of memory, attention, language and other thinking skills. Read more
N
- Neurofibrillary tangles
- Twisted strands of tau protein inside brain cells; a hallmark of Alzheimer's. Read more
- Neurologist
- A doctor who specializes in the brain and nervous system.
- Neuron
- A nerve cell; the brain's basic signaling unit. Read more
- Neuroplasticity
- The brain's ability to change and form new connections throughout life. Read more
- Neuropsychological testing
- Detailed testing of thinking skills by a specialist, often taking several hours. Read more
- Normal pressure hydrocephalus (NPH)
- Buildup of fluid in the brain causing walking problems, bladder control problems and memory loss; sometimes treatable with a shunt. Read more
P
- p-tau217
- A form of tau protein measurable in blood that is a strong marker of Alzheimer's brain changes. Read more
- Parkinson's disease dementia
- Dementia that develops a year or more after Parkinson's movement symptoms begin.
- Plaques
- Clumps of beta-amyloid protein between brain cells. Read more
- Prion
- A misfolded protein that causes other proteins to misfold; the cause of CJD.
- Procedural memory
- Memory for skills and habits, like tying shoes; often preserved until late in dementia. Read more
R
- Respite care
- Short-term care that gives a family caregiver a break.
- Rivastigmine
- A cholinesterase inhibitor available as a pill or skin patch. Read more
S
- Semantic memory
- Memory for facts and general knowledge, like the meaning of words. Read more
- Short-term memory
- Holding a small amount of information in mind for seconds to minutes. Read more
- Sundowning
- Increased confusion, anxiety or agitation in the late afternoon and evening. Read more
- Synapse
- The tiny gap where one neuron passes a signal to another. Read more
T
- Tau
- A protein that normally stabilizes brain cells; in Alzheimer's it forms tangles. Read more
V
- Vascular dementia
- Dementia caused by reduced blood flow to the brain, often after strokes or from small vessel disease. Read more
W
- Wandering
- Walking or leaving home without a clear purpose, with risk of getting lost.
- Working memory
- Holding and using information in mind for a short time, like a phone number while dialing. Read more
Y
- Young-onset dementia
- Dementia that begins before age 65. Read more