When it comes to the battle of the sexes, it is the number one issue which has long provoked controversy. However, now the biggest study of its kind, led by Scottish researchers, has taken the first steps towards unravelling the differences between the brains of men and women.

The research is based on analysis of brain imaging scans from more than 5,000 people taking part in the UK Biobank study, a long-term project to gather health information from thousands of volunteers which can be used by researchers to investigate a wide range of illnesses and diseases.

It has resulted in an ‘atlas’ mapping the differences between the brains of men and women, which shows the brains of males have a larger overall volume – even accounting for differences in body size - and surface area. Women, meanwhile, were found to have a thicker cortex – the outer layer of the brain also known as grey matter. At the moment, that's all we know - what the significance is we have yet to learn, although that is the task the researchers are to now undertake.

Loading article content

With debate long raging over whether the existence of a male or female brain can explain behavioural differences between the sexes, researchers have cautioned the study findings at the moment relate only to biological variations.

Study leader Stuart Ritchie, post-doctoral fellow at Edinburgh University's psychology department, said most studies which had been carried out on this issue used only a small sample of people – typically less than 100 - as carrying out MRI brain scans was expensive for researchers.

He said: “We thought given there is this [UK Biobank] dataset available, why don’t we have a look at the question of sex differences. It is something I have been interested in as we know there are differences in the prevalence of psychiatric diseases and disorders between male and females – so for instance, males have a higher rate of autism and schizophrenia, while in females Alzheimer’s in higher in prevalence.”

The team measured more than 60 different regions of the brain, to create an ‘atlas’ mapping out the variations between the sexes.

Ritchie said the three principle areas measured were the brain’s volume, surface area and the thickness of the cortex.

“We found males had a larger overall volume in their brain and a larger surface of the brain – but females had a thicker cortex,” he said. “All of these things have been linked to a better performance on IQ tests - generally people who are doing better in brain health have higher volume, higher surface area and higher thickness [of cortex]. Even though males were doing better on one thing, females were doing better on another.”

Ritchie said the differences found were “pretty large”, but cautioned that the study – which has been published online but is yet to be peer-reviewed – did not measure any differences in risk of disease or behaviour.

He said more research would be needed to link up the findings from the brain atlas with existing evidence in psychology literature for example, of males having higher levels of aggression or females performing better on social perception tests. “When it comes to trying to explain differences in behaviour, that is the next step,” he said.

Measuring the brain differences between men and women has provoked much controversy in the past, with research historically being used to label women as less intelligent or rational

The 19th century French anthropologist Paul Broca used measurements gathered from autopsies showing male brains weighed more than female brains to conclude that: “We are therefore permitted to suppose that the relatively small size of the female brain depends in part upon her physical inferiority and in part upon her intellectual inferiority.”

In recent years Gina Rippon, professor of cognitive neuroimaging at Aston University in Birmingham, has argued there is no such thing as a male or female brain and studies into the human brain need to stop focusing on sex and look at differences being attributed to cultural and environmental factors.

She questioned some of the findings in the new study, such as brain volume, which she said could be related to many different physical factors apart from sex, such as height, weight and head size.

Ritchie acknowledged that finding biological differences between the sexes was a “touchy subject”, but said it should not have any kind of moral or social implications.

“I think people make the mistake of saying if you are saying women have a smaller brain volume, does that mean you think they are inferior in some way?” he said. “Of course not, that would be a massive leap from the research. We are saying this is an interesting question because there are behavioural differences [between the sexes] and differences in psychiatric disorders – so we need to try and understand that for reasons of health and medical research. We shouldn’t ignore the fact there are these big differences by sex in the brain.”