A recent study suggests that the most commonly
found interaction may operate on the level of the cerebral
cortex. Chiang et al. (2011) assessed cortical white matter
integrity with diffusion tensor imaging in 705 twins and
their siblings. They demonstrated that white matter integrity
was highly heritable and, moreover, that there were
significant Gene Environment interactions, such that
heritabilities were higher among twins with higher SES and
higher IQ scores.