The finding that differences in anatomy between individuals are more because of genetic influences in some brain regions and environmental influences in others raises questions regarding implications for the associated cognitive functions. In the study by Thompson, Cannon, et al. (2001), the same regions that were highly heritable were also those that correlated most strongly with cognitive ability. A multivariate analysis of IQ and brain gray and white matter volumes in a sample of 24 MZ pairs, 31 DZ pairs, and 25 additional siblings found that the association between IQ and gray and white matter volumes was because of genetic rather than environmental factors (Posthuma et al., 2002). A second study by the same group using voxel-based morphometry described more focal heritable regions of both gray and white matter, which appeared to be affected by common genetic factors with IQ (Hulshoff Pol et al., 2006).
