Structural Brain Differences Between Sexes Significant

June 11th, 2011 by Pelle Billing

In a research report that is more than six years old, Richard J. Haier and his research team outline how men and women achieve similar levels of intelligence in different ways.

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.

brain_gender

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.

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18 Responses to “Structural Brain Differences Between Sexes Significant”

  1. James Barrow Says:

    Thanks for finding this Pelle.

    Great detective work in finding this report- 6 years old and hardly anyone seems to have heard about it.

    P: “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.”

    I agree. I was never convinced by the arguments for gender differences being socially constructed. Most of these arguments were being developed before the field of evolutionary biology had hardly emerged. If male and female humans evolved carrying out different tasks, then it is not too surprising to find their brain structures now differ (but it’s always good to have the scientific evidence!)

    Thanks again Pelle.

  2. Pelle Billing Says:

    You’re welcome, James. Good that it was useful to you.

  3. mananon Says:

    Such startling differences to achieve the same general level of intelligence. Perhaps this means men and women really are ‘equal but different’, at least as far as IQ is concerned.

    For me, the most important implications are in the way children are educated, particularly with regards to the differences in how boys and girls learn and behave in school. When I see a study like this the phrase ‘learning styles’ comes to mind. Teachers (or at least a good deal of them) insist whatever differences that exist are socially constructed. But it’s surely past the time when educators need to recognise these quite large innate differences and change the way they teach our children.

    I’m sure you agree this is very important, since the current refusal to recognise the innate differences in the ways male and female brains work means educators continue to force girls and boys to learn in the same way, often to the disadvantage of boys. A study like this is a valuable tool to persuade experts in education to finally recognise the overall differences between girls’ and boys’ learning styles, and change classroom environments and teaching methods for both sexes accordingly.

    Thanks Pelle Billing for an eye opening article.

  4. Pelle Billing Says:

    mananon,

    Yes, over time this kind of research needs to influence teaching. And it will – no educator will be able to avoid the new knowledge when it really starts to pile up.

  5. rightsformen Says:

    Hi guys,
    there are a lot of papers listed on http://www.sciencedirect.com

    Keywords: Sex differences, IQ …

  6. Pete Barnes Says:

    http://www.sciencedirect.com/science/article/pii/0191886994900302

    “Males have larger brains than females, even when corrected for body size, and brain size is positively correlated with intelligence. This leads to the expectation that males should have higher average levels of intelligence than females. Yet the consensus view is that there is no sex difference in general intelligence. An examination of the literature shows that the consensus view is wrong. Among adults, males have slightly higher verbal and reasoning abilities than females and a more pronounced superiority on spatial abilities. If the three abilities are combined to form general intelligence, the mean for males is 4 IQ points higher than the mean for females.”

  7. Pelle Billing Says:

    Pete,

    Yes, I’ve read about that before but this is the first time I see an actual research report about it. I’d love to see more links about this if anyone has it.

  8. Pete Barnes Says:

    The potential for political correctness to abolish a 4 IQ point difference is both impressive and disturbing.

  9. Törnrosa Says:

    Pelle: Begrep ju inte allt så klart, men var jag inte lite inne på detta i en tråd hos dig, där jag kunde tänka mig delvis könsuppdelad undervisning, eller något åt det hållet?

  10. Pelle Billing Says:

    Törnrosa: English only on this blog :)

  11. Törnrosa Says:

    OK But it was in swedish just above so. Sorry :-)

  12. Roger Says:

    Ok, but the brain is Plastic so structural diffrences could just aswell be a consequence of social environment and upbringing as it could be biological.

  13. Pelle Billing Says:

    Roger,

    Yes, the brain is plastic but it is highly unlikely that these differences are the result of plasticity.

    Brain plasticity reacts to our upbringing, our interests, how we spend our time, etc – and these are very different between individuals. The social gender conditioning prescribes certain tendencies but allows us many different ways to “be a boy” or “be a girl”. So social gender conditioning would not be able to create these kinds of striking sex differences.

    In fact, I doubt that any kind of plasticity could create these large differences.

  14. Pete Barnes Says:

    Agreed, Pelle. Men have bigger brains, more neurons, different ratios of neurons, and different emphasis on various brain structures. Attributing this to upbringing is … folly.

    Women and men are two important branches of humanity that specialize in different tasks. Our brains are slightly different, and we specialize in different tasks. Sadly, it has been increasingly politically correct to ignore this and attack those who admit it.

  15. Hayley Says:

    Hello

    This is an extremely interesting and useful article. I am aware of the variation of white and gray matter alongside other neurological and pysiological differences. However, i wondered whether the plasicity of mylein is correlated with the density of the white matter?

  16. Pelle Billing Says:

    Hayley,

    The short answer: I simply don’t know. If anyone does, then feel free to chime in.

    Glad you liked the article.

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