Cortical volume and developmental instability are independent predictors of general intellectual ability

Measures of developmental instability (DI) reflect developmental disruptions due to genetic and environmental perturbations during normal development. DI might be expected to influence the developmental course of brain development and hence intelligence, and several studies indicate this to be the case. The factors that mediate this relationship are unknown. One possibility is that DI affects intelligence through effects on cortical size. To investigate this possibility, we assessed a measure of DI, body fluctuating asymmetry (FA), the Raven's Advanced Progressive Matrices (RAPM), and other cognitive tests on a group of 19 healthy male volunteers on whom cortical volume, white matter, overall brain volume, and cross-sectional areas of the corpus callosum and planum temporale were measured. Both FA and cortical volume significantly predicted RAPM scores, but were not significantly correlated themselves. Multiple regression analyses yielded effects of FA on RAPM scores and a general intelligence principal component independent of cortical volume. Hence, it appears that developmental instability affects intellectual functioning through pathways not involving cortical volume. Possible mediators include macro-organizational structure, neural integrity, or metabolic efficiency.