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Sex and the brain

Sex and the brain

We’re finding ever more biological differences between male and female brains, but are a long way from grasping the implications

But Do men and women’s brains differ?

Yes. For decades, scientists have been aware of obvious differences in their size and shape. For a start, the average male’s is about 10% larger than the average female’s. And as imaging techniques, such as MRI scans, have improved, neuroscientists have noticed more and more distinctive “male” and “female” features: everything from the imprint of particular genes, to our vulnerability to certain diseases. The great challenge is to figure out how these physical and anatomical differences connect to our behaviour and our social roles. Is there a biological basis for the fact that only 8% of British engineers are women and just 12% of primary school teachers men?

What does the evidence say?

A recent influential study, led by Professor Simon Baron-Cohen at Cambridge University, suggests that babies in the womb with high levels of testosterone go on to exhibit classic male “systemising” abilities in later childhood; conversely, those with low levels tend to exhibit more female “empathising” skills. All brains start out female, but male foetuses experience a surge of testosterone at about eight weeks gestation, and this begins to alter the brain’s structure, killing off cells in some areas, and enhancing growth in others. The Cambridge team, which traced the development of children from pregnancy to the age of 12, found this had a major impact on how “male” or “female” our brains eventually become. “The higher the child’s pre-natal testosterone,” Baron-Cohen told the BBC, “the slower they were to develop socially. They showed, for example, less eye contact at their first birthday.”

And do men and women process information differently?

It would seem so. Researchers at the University of Pennsylvania, who mapped the neural pathways of 521 females and 428 males ranging in age from eight to 22, have found that male and female brains make different connections. “These maps show us a stark difference, and complementarity, in the architecture of the human brain,” says radiology professor Ragini Verma, who helped lead the study (published last December). The maps showed that male brains tend to make stronger connections between front and back: between the visual cortex (what we see) and the cerebellum (which controls our physical response); female brains showed more connections between left and right hemispheres, suggesting greater mastery of language, memory, intuition and emotional intelligence. The researchers suggested that these connections originally helped men to become good hunters and women good mothers – “a potential neural basis [explaining] why men excel at certain tasks, and women at others”.

So are we hardwired from birth?

It’s not as simple as that. One of the other important recent discoveries about our brains is just how much they change – expand and shrink and alter – throughout our lives, especially in adolescence. In the Pennsylvania study, the differences between male and female brain connections were only visible in those over 13, suggesting we are not born to think in particular patterns. In 2009, scientists at the University of Iowa were surprised to discover that a narrow strip of the cerebral cortex associated with social skills and emotional judgement – which tends to be larger in women – was nonetheless larger in boys than in girls. For this reason, neuroscientists tend to be very careful about declaring any conclusive meaning behind their results when talking about the sexes. They also prefer to describe a spectrum of gender, from “extreme male” to “extreme female” – acknowledging that virtually all brains are likely to be a mixture of the two.

Even so, nature dominates nurture?

Honestly, no one knows. For example, it is not at all clear whether that strip of the cerebral cortex – “the straight gyrus” – ends up larger in women as a result of certain sex-specific hormones or, as Scientific American puts it, as a result of “living 30 years in a group that practises greater empathetic responding”. Sociological studies examining the different ways men and women perform in cognitive tasks, have found this to be affected by a host of factors including prosperity, fertility rates, education and prejudice. One such study, led by the International Institute for Applied Systems Analysis in Vienna, tested the maths and memory skills of 31,000 over-50s across Europe. It found that younger participants – who’d grown up in richer, healthier, better-educated societies – tended to do better than their elders; that across Europe, men did better at maths tests, women at the memory ones; but that in the more prosperous, egalitarian north of Europe, the gap on the maths was much closer and women extended their lead in the memory tests. The likely explanation is that stereotypes and social barriers are still holding women back. As recently as 2012, researchers at Texas University found that US maths teachers regard female students as having lower abilities than their male counterparts – despite having the same test scores.

Then do our biological differences actually matter?

Ultimately, yes. For a start, men and women suffer strikingly different neurological diseases, so getting to the bottom of our brains is going to be ever more important for our health (see box). More generally, the more we understand about our brains, the more effectively we’re likely to use them. Acknowledging that boys and girls might approach a problem differently doesn’t mean they won’t come up with equally good solutions. Only 1.7% of British girls took physics A-level in 2014, but those that did achieved better results than their male counterparts. Gina Rippon, a neuroscientist at Aston University, thinks gender stereotyping is a big reason so few girls tackle physics; but the way questions are presented is another. “We know that girls’ performance on spatial cognition tasks can be improved if the problems are framed differently,” she says. “But these sort of findings are rarely used to inform how subjects such as physics are taught.”

Men’s problems, women’s problems

Dr Ruben Gur, who led the University of Pennsylvania brain imaging study, thinks the main value of its findings may lie in helping to discover “the roots of neurological disorders, which are often sex-related”. Men and women suffer from noticeably different brain problems and mental illnesses, with males more likely to be afflicted by autism, Parkinson’s disease, attention deficit syndrome, dyslexia and addiction; while women are more likely to suffer conditions such as depression, eating disorders, panic attacks and chronic pain.

A study at University College London last year of 100 brains and spinal cords removed during post-mortems identified strong genetic differences between the sexes in 12 regions of the brain. It found that some genes – such as NRXN3, which has been implicated in autism – were more likely to be expressed in male brains; and that the reverse was true with others. The presence of different genes raises the possibility of different drugs and treatments for men and women. Men are already known to be more receptive to paracetamol for headaches; women get better relief from opioids. According to Professor Jeffrey Mogil of McGill University, it’s just a matter of time before certain pain medications “will work in one sex and simply not work in the other sex”.

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