Cortical thickness declines more steeply with age than surface area and is more strongly associated with longitudinal change in fluid cognition, so thickness appears to be a more sensitive marker of dynamic neurobiological processes in cognitive aging, whereas area seems to reflect primarily stable, trait-like variation in cognitive ability.
Cortical thickness declines more steeply with age than surface area across adulthood.
Thickness shows stronger associations than area with longitudinal change in fluid cognitive abilities, fairly uniformly across the cortex.
Cognitive change depends on baseline thickness, independent of thickness change and of baseline cognitive ability.
Surface area is relatively stable across adulthood and shows weaker, more heterogeneous associations with cognitive change.
The findings suggest thickness indexes dynamic neurobiological processes underlying cognitive aging, whereas area reflects stable, trait-like variation in cognitive ability.
This study asked whether two components of the brain's outer layer, the cortex, relate differently to cognitive aging. Cortical volume, often used as a marker of brain aging, is the product of cortical thickness and surface area. These two features have different genetic and developmental origins. The researchers analyzed brain scans and cognitive tests from three groups of adults (Cam-CAN, OASIS-3 and HABS-HD), covering wide age ranges and different follow-up times. The replication cohorts' analyses were pre-registered. Thickness declined more steeply with age than surface area did, and it was more strongly linked to changes in fluid cognitive abilities over time. These links were fairly similar across the cortex. People with thicker cortex at baseline showed different cognitive change later, even after accounting for how much their thickness changed and how well they performed at the start. Surface area stayed comparatively stable through adulthood until old age, and its links to cognitive change were weaker and varied more across regions. This research suggests that thickness may be a more sensitive marker of the ongoing biological processes behind cognitive aging. Surface area may instead reflect stable, lifelong differences in cognitive ability. Treating the two measures separately, rather than relying on volume alone, may help explain why earlier studies gave inconsistent results.
Demetriou I, Correia M, Vidal-Piñeiro D, Fisher S, Eising E, Escott-Price V, et al.. (2026). Dissociable contributions of cortical thickness and surface area to cognitive aging: evidence from multiple longitudinal cohorts.. Cerebral cortex (New York, N.Y. : 1991). https://doi.org/10.1093/cercor/bhag181