Glossary
A working dictionary of brain health terms. Plain English up top, technical references underneath. 36 entries so far, growing.
A
Alzheimer's disease
A progressive neurodegenerative disease that gradually destroys memory and cognition. The most common cause of dementia worldwide.
Amygdala
Almond-shaped structures deep in each temporal lobe, central to emotional learning, fear processing, and the encoding of emotionally significant memories.
Amyloid plaques
Sticky clumps of beta-amyloid protein that accumulate between neurons. One of the two defining pathological features of Alzheimer's disease.
Atrophy
The loss of brain tissue volume or cortical thickness over time, reflecting a reduction in the size or number of neurons and their supporting cells.
B
Basal ganglia
A group of deep brain nuclei that coordinate voluntary movement, the learning of habits, and motivation. Central to Parkinson's disease.
Brain age
An estimate of how old your brain appears structurally compared to a healthy reference population, derived from a single MRI scan.
Brain age gap
The difference between brain age and chronological age. A positive gap means the brain looks older than it should; a negative gap, younger.
C
Cerebellum
The cauliflower-shaped structure tucked under the back of the brain — long known for movement, increasingly recognised for cognition and learning.
Cerebral cortex
The folded outer layer of the brain — only a few millimetres thick, but where most conscious thought, perception, and action happens.
Cerebrospinal fluid
The clear fluid that surrounds and cushions the brain and spinal cord, circulates through the ventricles, and plays a key role in waste clearance from the brain.
Cognitive reserve
The brain's accumulated resilience against pathology — built over a lifetime through education, cognitive engagement, and social activity — which allows some people to sustain function despite significant structural brain changes.
Corpus callosum
The largest white matter tract in the brain, connecting the two hemispheres with around 200 million axons.
Cortical thickness
The thickness of the brain's outer grey-matter ribbon (the cortex), measured millimetre-by-millimetre across its surface from a structural MRI.
D
Default mode network
A set of brain regions that are most active when the mind is at rest and not focused on an external task — linked to self-referential thinking, memory retrieval, and mind-wandering.
Dementia / Alzheimer's disease
Dementia is a syndrome of progressive cognitive decline severe enough to impair daily life; Alzheimer's disease is its most common cause, characterised by amyloid plaques, tau tangles, and gradual neurodegeneration.
Diffusion tensor imaging
An MRI technique that measures how water diffuses through brain tissue — sensitive to the microstructure of white matter tracts.
E
F
FLAIR sequence
An MRI sequence that suppresses the signal from cerebrospinal fluid, making lesions in the brain stand out brightly. The standard view for white matter pathology.
FreeSurfer / FastSurfer
Software pipelines that automatically segment the brain from an MRI scan and extract morphometric measurements such as cortical thickness and regional volume.
Functional MRI
An MRI technique that maps brain activity by detecting changes in blood oxygenation as different brain regions work harder or rest.
G
Glymphatic system
A brain-wide network of fluid channels, driven largely during sleep, that clears metabolic waste — including proteins linked to neurodegeneration — from brain tissue.
Gray matter
The darker, neuron-rich tissue that forms the outer cortex and the deep nuclei of the brain — where most signal processing happens.
H
M
Memory
The brain's ability to encode, store, and retrieve information. Multiple distinct systems with different anatomical homes and different vulnerabilities.
Mild cognitive impairment
A clinical state of cognitive decline that is noticeable and measurable, but not severe enough to interfere meaningfully with daily life.
Mini-Mental State Examination
A 30-point clinician-administered cognitive screen that takes about 10 minutes — one of the oldest and most widely used dementia screens.
Montreal Cognitive Assessment
A 30-point cognitive screening test that takes about 10 minutes — designed to be more sensitive than the MMSE to mild cognitive impairment.
MRI
A non-invasive imaging technique that uses strong magnetic fields and radio waves to produce detailed images of the brain's soft tissue structure.
Myelin
The fatty insulating sheath wrapped around axons, allowing electrical signals to travel up to a hundred times faster than along bare nerve fibres.
N
P
S
T
T1-weighted MRI
The standard MRI sequence for brain morphometry. Grey matter appears dark, white matter bright, and cerebrospinal fluid very dark — making tissue boundaries easy to measure.
Thalamus
A pair of large nuclei deep in the centre of the brain that act as the relay station for almost all sensory and motor information.
W
White matter
The bundles of myelinated axons that connect different regions of the brain — the brain's wiring, as opposed to its computing cells.
White matter hyperintensity
Bright spots in deep white matter on certain MRI sequences — markers of small vessel disease and accumulated cerebrovascular injury.