Structural brain indicators of cognitive performance in middle and late adulthood: The Human Connectome Project in Aging/Aging Adult Brain Connectome cohort.

Although cortical thinning and atrophy are well documented in aging and neurodegenerative disease, the cortical structural features associated with preserved or superior cognition across typical adulthood remain incompletely characterized. We examined associations between cortical thickness and cognitive performance in a large, typically aging cohort and tested whether they vary by age and cognitive domain. We analyzed cross-sectional data from cognitively healthy adults in the Human Connectome Project-Aging/Aging Adult Brain Connectome, spanning middle (36-59 years), early older (60-79), and late older (80 +) adulthood. Sex-stratified, age-residualized factor scores for memory, fluid, and crystallized abilities classified participants as high, middle, and low performers. Whole-brain cortical thickness was compared across groups. Descriptively, the largest and most consistent effects were observed for fluid abilities in midlife, with higher performance associated with greater thickness in bilateral somatomotor, visual, and auditory cortices. These effects spanned multiple sensory and motor regions and were replicated in stringent subsamples, including longitudinally stable and cross-domain high-performance groups. The observed patterns appear to be driven primarily by reduced thickness in low performers rather than by a distinct structural signature of high performers. Differences in cortical thickness between performance groups diminished with advancing age. These findings are consistent with the possibility that greater cortical thickness in sensory and motor cortices reflects a developmental structural advantage associated with higher fluid intelligence during middle adulthood. However, this advantage may not be sufficient to sustain high cognitive performance in later life, when other neural mechanisms may become increasingly important.