It appears that while men and women have the same average IQ, the level of cognitive function is achieved in very different ways. Not only do women and men employ different brain regions, there is also a vast difference in the emphasis on gray and white matter.
Let’s take a look at what the researchers have done:
Here, we examine whether there are male and female differences in the correlations between IQ and GM [gray matter] or WM [white matter] volumes based on optimized voxel-based morphometry (VBM) of structural MRI data.
Not only do the researcher want to investigate if men and women use different regions to create their intelligence, they want to check if the white matter or the gray matter is “doing the heavy lifting” in the areas that are important.
If they can demonstrate these kinds deep structural differences – directly linked to functioning – in men’s and women’s brain, it will be a significant finding. Previous research has demonstrated several functional sex differences in the brain, but without the kind of unquestionable link to brain structures that the researchers are aiming for:
Functional brain imaging studies have reported a number of sex differences (Cahill et al., 2001; Gur et al., 2000; Haier and Benbow, 1995; Mansour et al., 1996; Neubauer et al., 2002; Shaywitz et al., 1995, 2001), but task-specific demands on cognitive resources with functional studies must always be considered as the task itself could affect interpretation of functional imaging results. Structural imaging correlated with off-line analyses of various cognitive performance measures and traits, on the other hand, can identify those differences in neuroanatomy which may underlie the cognitive measure of interest, irrespective of any task design constraints.
Never mind if you don’t want to grasp every technical detail; the main thing to remember here is that they are checking whether men and women use different brain regions to achieve similar intellectual functioning, and whether men and women rely on gray/white matter in the same way.
Here are the results:
These present results highlight an important dissociation of brain morphology related to intellectual functioning in normal adult brains, as the pattern of voxel types and voxel locations linked with intellectual functioning differed substantially between the sexes.
The regions employed in intellectual performance are far from the same in men and women – a somewhat startling finding perhaps. Even more shocking is that the sexes use gray and white matter in such different ways:
With respect to voxel types, men had roughly 6.5 times the number of GM [gray matter] voxels identified as related to intellectual functioning as did women, and women had roughly nine times more WM [white matter] voxels than did men.
6.5 times the number and roughly nine times more? That’s beyond significant.
These findings – as interesting as they are in their own right – also throw the next, inevitable question at us. If women and men use different neural substrates to achieve a similar general level of intelligence, are there any differences in subsets of cognitive performance?
The current results contribute to a growing body of evidence demonstrating that, although the sexes do not differ in general intellectual ability, the neural substrates of general intelligence are different. Whether similar neuroanatomical differences are associated with specific mental abilities (assessed for example by WAIS subtests) remains to be determined; our VIQ and PIQ findings need replication with larger samples.
It would be highly surprising if such marked differences in brain regions/tissue employed in cognitive functioning do not translate into different ways of processing information, integrating memory, experiencing emotion, etc.
If anyone is skeptical of the hereditary component in these gender differences – perhaps wondering if they can solely attributed to men’s and women’s different gender roles – then the researchers put that fear to rest (see the first phrase):
Although GM and WM volumes are highly hereditable in many areas (Posthuma et al., 2002; Thompson et al., 2001), there is evidence that GM volume in humans can increase with motor learning (Draganski et al., 2004) or the acquisition of a second language (Mechelli et al., 2004) and the nature of genetic determinism in general is now controversial (Silverman, 2004).
My own take on this research is that it’s amazing to see that the general level of complexity of a system (such as the brain), determines overall functioning to a higher degree than the specific components. This is why men and women have similar intelligence even though our brains are quite different.
I also feel that the research on gender specific brain differences has come far enough to once and for all let go of the belief that gender is mainly constructed, and innate factors simply a minor concern. Men and women have brains with clear differences in anatomy and physiology, and it is highly unlikely that this wouldn’t affect our conscious and unconscious brain processes. as well as our behavior in the world.