The brains of men and women operate differently, scientists have shown for the first time in a breakthrough that shows sex does matter in how people think and behave.
The issue of whether male and female brains are distinct has proven controversial, with some academics arguing it is society – rather than biology – that shapes divergence.
There has never been any definitive proof of difference in activity in the brains of men and women, but Stanford University has shown that it is possible to tell the sexes apart based on activity in “hotspot” areas.
They include the “default mode network”, an area of the brain thought to be the neurological centre for “self”, and is important in introspection and retrieving personal memories.
The limbic system is also implicated, which helps regulate emotion, memory and deals with sexual stimulation, and striatum, which is important in habit forming and rewards.
Experts said the brain differences could influence how males and females view themselves, how they interact with other people and how they recall past experiences.
Dr Vinod Menon, professor of psychiatry and behavioural sciences at Stanford, said: “This is a very strong piece of evidence that sex is a robust determinant of human brain organisation.”
“Our findings suggest that differences in brain activity patterns across these key brain regions contribute to sex-specific variations in cognitive functioning.”
However, he added that further research is needed to fully understand the implications of the findings.
It is well known that male and female chromosomes release sex-specific hormones in the brain, particularly in early development, puberty and during aging.
There are also marked differences in how women and men perform in the real world.
Women tend to be better at reading comprehension and writing ability on average, and have good long-term memory.
Conversely, men seem to have stronger visual and spatial awareness and better working memory.
Yet scientists have struggled to spot these differences in neural activity, with brain structures looking the same in men and women.
AI behind breakthrough
For the research, the team used “explainable AI” – a type of computer learning that can sift through vast amounts of data to explain why an effect is taking place.
The model was shown MRI scans of working brains and told whether it was looking at a woman or man. Over time, the neural network began to pick out subtle differences between the two sexes that had been missed by humans.
When the researchers tested the model on about 1500 brain scans, it was able to tell if the scan came from a woman or a man more than 90 per cent of the time.
Dr Gina Rippon, emeritus professor of cognitive neuroimaging at the Aston Brain Centre and author of The Gendered Brain, has argued that society is to blame for brain differences in men and women.
Commenting on the study, she said: “The really intriguing issue is that those areas of the brain which are most reliably distinguishing the sexes are key parts of the social brain.
“The key issue is whether these differences are a product of sex-specific, biological influences, or of brain-changing gendered experiences. Or both. Are we really looking at sex differences? Or gender differences?
“Or, acknowledging that almost all brain–shaping factors are dynamically entangled products of both sex and gender influences, are we looking at what should be called sex/gender differences?”
‘Sex-specific vulnerabilities’
Experts are hopeful that finding differences between male and female brains could be crucial in tackling neurological or psychiatric conditions that affect women and men differently.
For example, women are twice as likely as men to experience clinical depression, while men are more at risk of drug and alcohol dependence and dyslexia. The brain areas discovered in the study are often associated with neurological disease.
Dr Menon added: “A key motivation for this study is that sex plays a crucial role in human brain development, in aging, and in the manifestation of psychiatric and neurological disorders.
“Identifying consistent and replicable sex differences in the healthy adult brain is a critical step toward a deeper understanding of sex-specific vulnerabilities in psychiatric and neurological disorders.”
Researchers said the AI model could answer other important questions about brain connectivity, cognitive ability, or behaviour, and they will be making it publicly available for any researchers to use.
The findings were published in the Proceedings of the National Academy of Sciences.
