Morphological variations and cortical atrophy of the precuneus in normal aging and Alzheimer's disease.

The precuneus is a central hub of the human brain, and its morphology displays a noticeable individual variability. It is larger in humans than in other primates, and it is affected by atrophy and hypometabolism in the early stages of Alzheimer's disease (AD). In this study, we compare its general morphology in normal aging subjects and AD patients, considering its geometry through shape analysis, and the atrophy at its boundary by quantifying the intersulcal spacing. Results suggest that the AD sample displays a reduction of the inferior regions of the precuneus, namely those that fade into the posterior cingulate and retrosplenial cortex. During aging, sulcal spacing is pronounced at the superior and posterior regions, although in the AD sample the latter change is more marked. However, these differences are associated with a remarkable individual variation and a consistent overlap between group ranges. This study stresses further the differences between the dorsal and ventral regions of the precuneus. Beyond functional factors, the dorsal areas represent a region of scarce spatial constraints, whereas the ventral regions are embedded in a complex topological environment. This structural difference must be considered when investigating cortical morphology in both normal and pathological conditions.