Intelligence and regional brain volumes in normal controls

The relationship between brain size and intelligence was examined in a large sample of healthy normal volunteers (N = 90). In addition to confirmation of the small but significant relationship between IQ and whole brain volume (r = 0.25, p < .05) using magnetic resonance imaging, regional differences were examined using a completely automated procedure to generate lobar volumes to address questions related to regional specificity and its relationship to intelligence. A significant positive relationship was found between measures of full scale IQ and frontal (r = 0.25, p < .05) and temporal (r = 0.28, p < .01) regions, although when correlations across different brain regions were tested against each other, there was no evidence of regional specificity. In addition, no laterality effects were seen. Correlations between WAIS-R subtest scores and brain regions indicated few correlations between verbal subtest scores and brain size, but several significant correlations between the performance subtest scores and frontal, temporal, parietal, and cerebellar brain regions. These results support the notion of a modest relationship between brain size and measures of global intelligence and suggest diffuse brain involvement on performance tasks which require integration and use of multiple cognitive domains.