Men's and Women's brains appear to age differently
There's been a lot of poorly thought-out stuff written about the differences between men's and women's brains and minds. In the worst instances, sexist commentators use spurious neuroscience claims to provide "evidence" for gender stereotypes — take John Gray of Men Are From Mars, Women Are From Venus fame, who says men can't multitask because they use one brain hemisphere at a time while women use two (not true), or Louann Brizendine, author of The Female Brain, who says women are more emotional and empathetic than men because they have more mirror neurons (ditto). But if you can get past all of this pseudoscience, there's some legitimately illuminating, serious medical research on sex-based brain differences — some of which has important health implications.
Consider one undeniable discovery in this area, which is that the sexes differ in their vulnerability to various neurological illnesses. For example, Parkinson's disease (which impairs people's ability to move and causes tremors) is more prevalent in men, and men tend to be diagnosed with the illness earlier than women; on the other hand, there's evidence that women are affected more rapidly and adversely by the brain-cell loss that's associated with Alzheimer's disease. Research into the differences between men's and women's brains could help shine a useful light on the physiological reasons underpinning these sex differences in disease vulnerability.
It's in that vein that a new brain-imaging study published in Brain Imaging and Behavior has made a small but important contribution, by showing that subcortical (deep) structures in the brain appear to age more quickly in men's brains than women's, possibly helping to explain why men are more susceptible to neurological illnesses that involve these structures, such as Parkinson's.
A team of neuroscientists led by András Király at the University of Szeged in Hungary scanned the brain structures of 53 men and 50 women matched for age. The average age of the participants was 32, with the youngest participant being 21 years old and the eldest 58. Some of the most obvious gender differences they found are already well established in the literature: For example, the men's brains were on average larger than the women's (a bigger brain doesn't necessarily make for a smarter brain; if it did, whales and elephants would be completing Ph.D.'s). But the researchers were particularly interested in the volume of the participants' subcortical structures: These are parts of the brain involved in movement control and emotional processing, as well as the thalamus, which is like the brain's main relay station for passing information between different parts of the brain.
After adjusting their data to account for the aforementioned overall gender difference in size, the researchers found several sex-based size differences in subcortical brain structures. For example, the women had more gray matter in the left and right hippocampus (a structure involved in memory), while the men had a larger caudate nucleus (involved in controlling voluntary movements) and larger thalamus. (Gray matter refers to brain tissue made up of neuronal cell bodies, as opposed to white matter, which consists of the insulated axons or tendrils via which brain cells communicate.)
Interestingly, the finding that the hippocampus tends to be larger in women has been reported many times in the literature, yet it contradicts a recent study that declared, after summarizing data from many prior investigations, that there is in fact no sex difference in this structure (prompting over-the-top pop-science headlines like "There is probably no such thing as a 'male' and 'female' brain").
This just shows once again how confusing and contradictory neuroscience can be, and how quick the media are to jump to extremes in the way they interpret this kind of research: One minute we're being told it's like the sexes are from different planets, the next minute that there are no differences at all. The messy reality is likely somewhere in between.
From a medical perspective, the most important insight from the new study has to do with sex-based changes in brain volume that correlated with participants' age: For example, while both sexes showed reduced total brain volume and thalamus volume with age, only the men showed age-related reductions in caudate nucleus and putamen volume (the putamen is another subcortical area involved in movement control). Furthermore, overall gray matter (including in subcortical areas) in the men's brains was found to reduce at a faster rate than in women's brains — which could be taken as a mark of faster brain aging in men.
This study can't explain why this brain-aging difference was observed, but the researchers speculate that age- and sex-related changes in hormone levels may play a part, combined with sex-related differences in how different brain structures respond to these hormonal changes. Lots more research is needed to unpick these complex effects. The new study also can't say whether the more rapid gray-matter loss in men's subcortical structures is related to their greater vulnerability to illnesses such as Parkinson's disease, or even to suicide (a recent paper linked suicidal behavior with specific areas of reduced subcortical gray matter), but this is definitely a possibility worth investigating.
What's clear is that we shouldn't sweep research on sex-based brain differences under the carpet in the interest of political correctness, just because some misguided writers use the field to make sweeping generalizations about men's and women's abilities and personalities. As neuroscientist Larry Cahill explained in a recent article for the Dana Foundation, and as these new findings show, "the biological mechanisms of brain aging and disease cannot be assumed to be the same in men and women."
Dr. Christian Jarrett (@Psych_Writer), a Science of Us contributing writer, is editor of the British Psychological Society's Research Digest blog. His latest book isGreat Myths of the Brain.
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