Study Finds Gender Inequality Associated To Differences In Brain Structure Between Sexes

A study, recently published by the top-tier journal, The Proceedings of the National Academy of Sciences (PNAS), has found strong evidence that country-level gender inequality (essentially women’s status in society relative to men) is related to differences in brain structure between the two sexes.

​​The multinational paper, entitled ‘Country-level gender inequality is associated with structural differences in the brains of women and men’, was co-authored by more than 80 researchers, including six from Stellenbosch University’s ​(SU) Department of Psychiatry. The SU researchers are Prof Laila Asmal, Dr Stefan Du Plessis, Prof Christine Lochner, Dr Hilmar Luckhoff, Dr Lebogang Phahladira and Dr Annerine Roos. Lochner and Roos are associated with the South African Medical Research Council (SAMRC) Unit on Risk and Resilience in Mental Disorders, while the other four researchers are with the University’s Psychosis Research Group.

Asmal, an associate professor and psychiatrist at SU and Tygerberg Hospital, said the study looked at a data set of nearly 8 000 MRI scans from 29 different countries, representing every continent.

“We know that men and women have different experiences of mental health problems and there are possibly many reasons for that,” says Asmal. “We were therefore particularly interested in gender differences in brain structure and the associations thereof with the environment.”

“We used a measure from the United Nations Development Programme to estimate country-level gender inequality. In countries with higher levels of gender inequality, women experience more discrimination, which restricts their access to educational, healthcare and employment opportunities. This discrimination also leads to women being more vulnerable to gender-based violence. If all those factors (violence, education, employment, and healthcare differences) are linked to gender inequality, it stands to reason that you could end up with differences in brain structure between men and women, because all those factors can affect brain development.”

Asmal said her team, as well as the team from the MRC Unit on Risk and Resilience in Mental Disorders contributed MRI brain scans from previous studies to the research. The lead investigator was the UK- and Chile-based Dr Nicolás Crossley, who has conducted interesting neuroimaging research in populations that are typically under-represented in research.

“Dr Crossley reach out to us through existing collaborative networks to discuss the concept and methodology of the study, and asked us to contribute our local South African data. The study combines data from 29 countries to compare how gender inequality in the different countries relates to brain thickness in different regions/areas of the brain.” According to Asmal, this was the first study to look at gender inequality at country level, and how it relates it to structural brain differences and cortical thickness differences between men and women.

“There was a significant effect in the brain across the board, globally. Specifically, the cortical thickness of the right hemisphere, especially in limbic regions such as the right caudal anterior cingulate and right medial orbitofrontal, as well as the left lateral occipital, present thinner cortices in women compared to men only in gender unequal countries.”

These findings are significant because they suggest a potential neural mechanism underlying the worse outcome of women in gender-unequal settings and they highlight the role of the environment in the brain differences between women and men. It is important to note that although societal and individual expressions of “gender” can vary greatly, available research data is limited to biological sex at present.

“So far, we have only established the relationship between gender inequality and brain structure. We still don’t know how this comes about. The exact nature of the differences is also being investigated. Previous research has shown similar regional brain changes related to stress, resilience to adversity, responses to inequity and negative comparisons. Nevertheless, the actual mechanism of the relationship is still unclear. The next step is to examine and understand the mechanism, and when it happens, for example, is it happening in childhood, is it happening at an older age, or is it happening across the board. Longitudinal data would be hugely helpful to continue this study on how women’s central nervous system faces and adapts to adversity and to develop novel intervention strategies where needed.”