Mars v. Venus: are men and women really different?

Last year, researchers researched that women taking Ambien, the sleep drug, were taking double the dose they should have been taken. This mistake was accredited to the fact that most drugs are tested only on males (first on male animals and then on male humans). The logic is that female hormones are complicated and males and females are basically the same, so it’s better to test the drug on the simpler sub-population and generalize the findings. Oops. Turns out women metabolize the drug differently, so the effective dose for women is much lower than for men, but because the prescribed doses were the same, women were consistently overdosing on Ambien. Here’s the 60 Minutes episode exploring this blunder. To correct it, the FDA ordered all sleep medications to be retested on both women and men. But what about all sorts of other medications that might deserve different recommended doses for women and men? It would be too expensive to retest them all, so we’re not going to do it.

This incident sheds a light on a difference between male and female bodies that can’t be ignored. Whether there are other differences, differences between the male and female brain, remains a contentious issue. This article by Larry Cahill, Equal ≠ The Same: Sex Differences in the Human Brain, presented some really compelling evidence for nontrivial differences in male and female brains.

Cahill cites one study by Ingalhaliker and colleagues that used diffusion tensor imaging (a form of MRI) to measure connectivity patterns of brain (how much different neurons connect with others, reflected by the amount of white matter in the brain) in 428 males and 521 females between the ages of 8 and 22. This huge sample led them to conclude that “male brains are optimized for intrahemispheric and female brains for interhemispheric communication.” In other words, male brains, on the whole, demonstrate more connectivity within each hemisphere, while there’s more connectivity between the two hemispheres in female brains. According to the authors, these findings “suggest that male brains are structured to facilitate connectivity between perception and coordinated action, whereas female brains are designed to facilitate communication between analytical and intuitive processing modes.” Maybe this is a post hoc explanation, but it seems pretty consistent with the bulk of males and females I know. (Also worth noting that, as to be expected with such a heated topic, there are disagreements about these researchers’ interpretation of the data).

Another informative study that Cahill writes about was conducted by Cribbs and colleagues. These researchers examined the patterns of expression of immune system-related genes implicated in Alzheimer’s and aging. It was already known that in general, these genes are expressed in the hippocampus and and the superior frontal gyrus, a part of the frontal cortex, but the researchers found that the superior frontal gyrus was more prone to immune-type gene reactions in males than it was in females, and the hippocampus was more prone in females than in males. The manifestation of Alzheimer’s Disease and aging may look similar in males and females, but the underlying mechanistic patterns may be different. If these researchers found this in one circumstance, what other medical conditions might arise differently in males and females?

Cahill summed the issue up eloquently:

At the root of the resistance to sex-influences research, especially regarding the human brain, is a deeply ingrained, implicit, false assumption that if men and women are equal, then men and women must be the same. This is false. The truth is that of course men and women are equal (all human beings are equal), but this does not mean that they are, on average, the same. 2 + 3 = 10 – 5, but these expressions are not the same. And, in fact, if two groups really are different on average in some respect, but they are being treated the same, then they are not being treated equally on average.

It’s a tough issue to resolve: how do we treat the two groups equally, but not the same? Parents of multiple children seem overall to solve this problem at least to a “good enough” extent, and I have faith that we can do the same on a larger scale in science.

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2 comments

  1. Interesting! Assuming Cahill is right, how did men’s and women’s brains become different? Here’s my speculation (and it’s definitely speculation!): We make and remake our brains as we live, right? And–maybe–sometimes–those brains we’ve made by living can even be passed down by genes (epigenetics)? So is there a chance that women’s adapting to situations in which they needed “communication between analytical and intuitive processing modes” is what made our brains that way?

    1. I like this idea a lot! Plus, culture probably plays a pretty big role in our brains’ plasticity. Even if parents try not to feed into gender stereotypes, I think there are so many that are just unavoidable…

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