Cortical thickness
Also known as: cortical thinning
The thickness of the brain's outer grey-matter ribbon (the cortex), measured millimetre-by-millimetre across its surface from a structural MRI.
Cortical thickness is a measurement of the depth of the cerebral cortex — the thin, folded sheet of grey matter on the outside of the brain where most of cognition happens. It varies from roughly 1 to 4.5 millimetres in healthy adults, depending on the region.
The measurement is made from a high-resolution structural MRI by:
- Identifying the boundary between cortex and white matter
- Identifying the boundary between cortex and cerebrospinal fluid
- Measuring the distance between those two surfaces at every point
Tools like FreeSurfer and FastSurfer produce these surfaces automatically and report thickness over hundreds of cortical parcels.
Why it matters
Cortical thickness declines with age, but not uniformly. Some regions thin faster (frontal cortex), others slower (occipital cortex). Patterns of thinning are characteristic of specific conditions:
- Alzheimer's disease — early thinning in entorhinal cortex and parietal regions
- Frontotemporal dementia — frontal and temporal pole thinning
- Healthy ageing — a more diffuse, gentler pattern
Thickness is more sensitive to subtle change than crude volume measurements — useful in early-stage neurodegeneration and in measuring treatment effects in trials.
In our work
Cortical thickness is one of the metrics we extract in our neuroimaging analytics service, alongside surface area, gyrification, and regional volumes.
Related terms