Men and women use different brain areas to achieve similar IQ results

Haier RJ, Jung RE, Yeo RA, Head K, Alkire MT. Structural brain variation and general intelligence. Neuroimage. 2004 Sep;23(1):425-33. PDF/HTML via ScienceDirect

Abstract. Total brain volume accounts for about 16% of the variance in general intelligence scores (IQ), but how volumes of specific regions-of-interest (ROIs) relate to IQ is not known. We used voxel-based morphometry (VBM) in two independent samples to identify substantial gray matter (GM) correlates of IQ. Based on statistical conjunction of both samples (N = 47; P < 0.05 corrected for multiple comparisons), more gray matter is associated with higher IQ in discrete Brodmann areas (BA) including frontal (BA 10, 46, 9), temporal (BA 21, 37, 22, 42), parietal (BA 43 and 3), and occipital (BA 19) lobes and near BA 39 for white matter (WM). These results underscore the distributed neural basis of intelligence and suggest a developmental course for volume–IQ relationships in adulthood. Keywords: IQ; Brain volume; Morphometry

This is an interesting paper in Neuroimage that seeks a structural correlation of white and gray matter with intelligence scores, in male and female subjects. The study was performed by Haier et al at UC-Irvine, and there is a good layman's summary at the UCI website, which makes the point:

The study shows women having more white matter and men more gray matter related to intellectual skill, revealing that no single neuroanatomical structure determines general intelligence and that different types of brain designs are capable of producing equivalent intellectual performance.

“These findings suggest that human evolution has created two different types of brains designed for equally intelligent behavior,” said Richard Haier, professor of psychology in the Department of Pediatrics and longtime human intelligence researcher, who led the study with colleagues at UCI and the University of New Mexico.
[...]
In general, men have approximately 6.5 times the amount of gray matter related to general intelligence than women, and women have nearly 10 times the amount of white matter related to intelligence than men. Gray matter represents information processing centers in the brain, and white matter represents the networking of – or connections between – these processing centers.

This, according to Rex Jung, a UNM neuropsychologist and co-author of the study, may help to explain why men tend to excel in tasks requiring more local processing (like mathematics), while women tend to excel at integrating and assimilating information from distributed gray-matter regions in the brain, such as required for language facility. These two very different neurological pathways and activity centers, however, result in equivalent overall performance on broad measures of cognitive ability, such as those found on intelligence tests.

These are fascinating results, especially since by eschewing the fMRI craze they have been able to exclude any number of confounding sources of correlation that might have undermined the results. Note that this is not the first study^[1] to investigate how IQ correlates with gray matter volume, but the gender dimorphism really adds a fascinating twist, especially in light of Harvard President Larry Summers' clumsily-expressed but nevertheless frank and thought-provoking thoughts on the topic of female academic achievement. This study demonstrates that men and women are equal but different, which is a common-sense result.


[1] Neuroimage. 2004 Nov;23(3):800-5, Nat Rev Neurosci. 2004 Jun;5(6):471-82.