Parieto-frontal gyrification and working memory in healthy adults.

Gyrification of the cortical mantle is a dynamic process that increases with cortical surface area and decreases with age. Increased gyrification is associated with higher scores on cognitive tasks in adults; however, the degree to which this relationship is independent of cortical surface area remains undefined. This study investigates whether regional variation in gyrification is associated with domain-general and domain-specific cognition. Our hypothesis is that increased local gyrification confers a functional advantage that is independent of surface area. To quantify regional gyrification, we computed the local gyrification index (LGI) at each vertex and averaged across a bilateral parietal-frontal region associated with general intelligence and reasoning (Jung and Haier 2007). A sample of 48 healthy adults (24 males/24 females; ages 18-68 years) completed a high-resolution 3 T T1-weighted MRI and standardized administration of the Wechsler Adult Intelligence Scale (WAIS). We found a positive correlation between cortical gyrification and working memory, which remained significant after controlling for cortical surface area. Results suggest that a higher degree of local cortical folding confers a functional advantage that is independent from surface area and evident for more dynamic or "fluid" cognitive processes (i.e., working memory) rather than over-learned or "crystallized" cognitive processes.