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Exploring Brain Differences: Male v Female

May 21, 2012  |  Amy Sandberg

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The human brain is a truly amazing organ. It controls body temperature, blood pressure, heart rate and breathing; takes in an infinite amount of information about the world using our senses; coordinates our physical movement when walking, talking, standing or sitting; and allows us to think, dream, reason and experience emotions.

And while the brain, like your mother, loves her children – male and female – the same, she loves them differently. One reason for this difference may have to do with the brain structure.

For starters, males have larger brains (and heads) on average than women, even when accounting for differences between male and female height and weight. The male brain is typically about ten percent larger than the female brain. Men also have approximately 6.5 times more gray matter than women. Women, however, have about 10 times more white matter than men (source: Carey) do and women’s brains neurons are more densely packed especially on the cortex of the brain (the command and control center for language and communication).

Researchers believe that men tend to think with their gray matter, which is full of active neurons while women tend to think with the white matter (source: Haier), which consists more of connections between the neurons (source: Witelson). It’s believed these differences between grey and white matter and density may allow a woman’s brain, while smaller in size, to work faster than a man’s, and may account for some of differences in how men and women think, feel and behave (source: Hotz).

Despite noticeable sex differences in brain structure and function, neither the density of women’s neurons, or the size of a man’s brain, are reliable predictors of intelligence. Although the extra mass does give males more processing power, this doesn’t make men more intelligent. Rather, scientists believe the reason for the increased brain mass (source: Shaywitz)  is to accommodate the bigger body mass and muscle groups of the male (source: Shaywitz).

Apart from white matter, how else do females compensate for the difference in size and processor speed? Using imaging studies, scientists have concluded that men and women access different sections of the brain when performing the same task. In one study, men and women were asked to sound out different words. Men relied on just one small area on the left side of the brain to complete the task, while the majority of women used areas in both sides of the brain, indicating that there is more than one way for the brain to arrive at the same result.

Researchers have long believed men to be sharply left-brain dominant (source: Baron-Cohen), while women were believed more evenly balanced between left and right-brain processing (source: Shaywitz). This may explain why women often have better communication skills and emotional intelligence than men, and why men can sometimes have trouble picking up on emotional cues unless they’re clearly verbalized – making for tricky communications between the sexes.

Because women tend to have a larger deep limbic system than men (source: Shaywitz), they’re more in touch with their feelings and are better at expressing their emotions. This makes women better at connecting with others, but unfortunately may also contribute to higher rates of depression. (source: Karolinska Institutet).

Brain structure has also proven important in the treatment of Traumatic Brain Injury (TBI). Research on veterans who’ve experienced (TBI) indicates that based on the location of neurons, brain injuries affect men and women differently (source: Bramlett and Dietrich). The differences in progesterone levels also account for some differences.

Another structural difference is the size of the inferior-parietal lobule, which controls numerical brain function. It is larger in males, and has been thought to account for the consistent male advantage on mathematical standardized tests. However, a few studies have demonstrated that the gender gap in mathematical skills may be subject to our perceptions and expectations. In one study, girls’ math scores improved when they were told that the exam was gender-neutral, while white men’s scores on the same test dropped when they were told the scores would be evaluated against Asian men’s scores. (source: Murphy).  This suggests that the situation is more fluid than just structural differences.

Sex differences in spatial skills are among the largest of the cognitive gaps. For decades researchers attributed this difference to the fact that the parietal region is thicker in the female brain, making it harder for them to mentally rotate objects. However, the actual size of the skill gap is much smaller in children than in adults. Evidence suggests that in addition to the difference in thickness of the parietal region, other factors may have greater explicatory power. One is culture. Boys are exposed to and have more visuospatial interests – building, throwing, navigating, shooting – than girls. The other is chemical. Evidence suggests that the early though relatively small spatial skill gap in small children is influenced by prenatal testosterone (soruce: Kucian). It is as yet unclear whether the widening divergence in spatial skills is influenced by chemical processes or because as males and females grow older the practice different skills.

In a followup, I will explore chemical differences in male and female brains that would explain differences between the sexes.

Sources

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Baron-Cohen, Sasha. Essential Difference: Men, Women and the Extreme Male Brain. Penguin, 2003

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Bramlett, Helen, Dietrich, W Dalton. Pathophysiology of Cerebral Ischemia and Brain Trauma: Similarities and Differences. Journal of Cerebral Blood Flow & Metabolism (2004) 24, 133–150; doi:10.1097/01.WCB.0000111614.19196.04

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