Positive correlations between corpus callosum thickness and intelligence

Abstract

Callosal morphology is thought to reflect the capacity for inter-hemispheric communication and thus, in addition to other cerebral characteristics, may serve as a neuroanatomical substrate of general intellectual capacity. We applied novel computational mesh-based methods to establish the presence and direction of correlations between intelligence and callosal thickness at high spatial resolution while removing the variance associated with overall brain size. Within healthy subjects (n=62), and within males (n=28) and females (n=34) separately, we observed significant positive correlations between callosal morphology and intelligence measures (full-scale, performance, and verbal). These relationships were pronounced in posterior callosal sections and were confirmed by permutation testing. Significant negative correlations were absent. Positive associations between intelligence and posterior callosal thickness may reflect a more efficient inter-hemispheric information transfer, positively affecting information processing and integration, and thus intellectual performance. At the same time, regional variations in callosal size might also partly reflect the underlying architecture of topographically connected cortical regions relevant for processing higher-order cognitive information. Our findings emphasize the importance of incorporating posterior (callosal) regions into the theories and models proposed to explain the anatomical substrates of intelligence.

Figure 1

Correlations between TBV and callosal thickness. Illustrated are correlation coefficients (top map) and associated significance values (bottom map). The upper color bar encodes the r-values that depict the magnitude and direction of correlations between TBV and callosal distance measures. The lower color bar encodes the p-values, with gray color indicating regions where no significant correlations between TBV and callosal distance measures were detected. The callosal anterior section is located on the left; the callosal posterior section points to the right.

Figure 2

Correlations between callosal thickness and intelligence. Partial correlation coefficients and associated significance values for full-scale IQ measurements are shown in the first and second columns of callosal maps, while significance values for performance and verbal IQ correlations are illustrated in the third and fourth column. Measurements are shown for the combined sample (first row), males (second row), and females (third row) separately. The fourth row depicts significant differences in the slopes of the gender-specific relationships (gender interaction). The left color bar encodes the r-values that depict the magnitude and direction of correlations between full-scale IQ measures and callosal distance measures. The right color bar encodes the significance associated with the partial correlations and also gender interactions associated with full-scale IQ, performance IQ, and verbal IQ.

Figure 3

Correlations between callosal thickness and intelligence. Partial regression plots showing relationships between full-scale IQ and callosal thickness (callosal residuals) at the most significant callosal surface point (point # 65), within the combined sample (left), and within males (top right) and females (bottom right). The most significant callosal surface point is located in the callosal posterior body, as marked by arrows.