Brain plasticity and intellectual ability are influenced by shared genes

Abstract

Although the adult brain is considered to be fully developed and stable until senescence when its size steadily decreases, such stability seems at odds with continued human (intellectual) development throughout life. Moreover, although variation in human brain size is highly heritable, we do not know the extent to which genes contribute to individual differences in brain plasticity. In this longitudinal magnetic resonance imaging study in twins, we report considerable thinning of the frontal cortex and thickening of the medial temporal cortex with increasing age and find this change to be heritable and partly related to cognitive ability. Specifically, adults with higher intelligence show attenuated cortical thinning and more pronounced cortical thickening over time than do subjects with average or below average IQ. Genes influencing variability in both intelligence and brain plasticity partly drive these associations. Thus, not only does the brain continue to change well into adulthood, these changes are functionally relevant because they are related to intelligence.

Figure 1.

Cortical thickness change in the adult human brain and intelligence. The cortical maps show the mean cortical thickening (left) and thinning (right) in mm change with age between 20 and 40 years. The graphs show the cortical thickness change in the parahippocampal cortex and superior frontal cortex for the three intelligence groups. The maximum change in cortical thickness was −0.026 mm per year.

Figure 2.

Heritability of cortical thickness and cortical thickness change showing the heritability (h²) of cortical thickness (left), the heritability of cortical thickness change (middle), and the χ² test statistics (χ², df = 1) of specific genetic influences on cortical thickness change, which are not associated with the genetic influences of absolute cortical thickness (right).