Study finds differences in men's and women's brains, but only in countries with greater gender inequality

Many studies have shown that in countries where gender inequality is greater, women are more at risk of mental illness and tend to be less successful in school than men. A person's brain, such as the amount of fat accumulated in the belly or the strength of the muscles, changes with the circumstances of the environment, although sometimes, hidden by the skull, those transformations do not seem so obvious. In China, for example, dementia has been found to be higher among women than men, and lack of exercise or illiteracy has been identified as risk factors for this type of disease.

To test whether the circumstances of greater or lesser inequality between the sexes are related to differences in the brain structure of men and women, an international group of scientists took almost 8,000 magnetic resonance images of people from 29 countries. In an article published in the journal PNAS, they state that in countries with greater gender equality, measured with the Gender Inequality Index and the Gender Gap Index, no significant differences were observed between the brains of one and the other. However, where there was greater inequality, they saw that the thickness of the right side of the cerebral cortex was lower in women.

The authors acknowledge the complexity of gender inequality indices that in turn interact with different biological mechanisms, but they have hypotheses to explain their observations. The anterior cingulate cortex and orbitofrontal, where thickness differences were found, have been linked to responses to inequality or resistance to adversity. In addition, changes have been seen in these regions in ailments where stress is considered a central mechanism and it has been seen how it is lost during depression or reduced by post-traumatic stress.

Read moreA decoder reads thoughts recorded by a brain scanner

Nicolás Crossley, a professor at the Pontificia Universidad Católica de Chile and co-author of the study, explains that this type of work points to an observable effect of gender inequality in the brain in people who are exposed to permanent subordination and even physical violence. Although the study does not establish a cause-and-effect relationship, and "these results are not necessary to argue that gender inequality is wrong," she believes it can lend weight to arguments in favor of policies that reduce inequality. "In all legislations, when there is an act of violence, if that act is associated with visual and significant changes in the other, the severity of the violence is considered greater. With our work, in a way, we show that there is a real damage product of gender inequality, "he defends.

Origin of differences

For Crossley, these results can also influence ideas about the origin of differences between men and women found in societies around the world: "There are people who argue that these differences in social roles are the result of biological differences and here we show that some of these differences can change by the social environment." In addition to influencing the way of seeing the origin of inequalities, the authors, in a phrase questioned by other colleagues who have not participated in the study, state in the introduction of their article that their results "provide initial evidence for policies for gender equality informed by neuroscience". According to the Chilean researcher, the ability to measure brain changes and relate them to changes in gender policies can serve to "monitor how certain public interventions are reflected in these brain measurements or tell us at which critical moments in a person's development it is most important to apply public policies."

A person undergoes a brain scan. Nolan Zunk/University of Texas at Austin

Bruce Wexler, a professor at Yale University, believes that "the most surprising thing would have been if the researchers had not found differences in the brains of men and women where women have much less intellectually stimulating jobs, have had little access to education or are not incentivized to engage in physical activity." "In addition, in those countries, they are subjected to violence, which we already know can affect brain volume, and the data cited by the authors showing more depression and other mental health problems must mean that there are changes in brain function and at some level of brain structure," Wexler explains. He is the author of the book Brain and Culture, in which he explores the synergies between human neuroplasticity and the fact that humans change their environment which, in turn, changes their brains.

Wexler questions whether the authors' assertion about the value of their results in promoting equality policies is substantiated. He believes that, "although the resonances, because of that ability to measure the brain, can impress some people and move them to act, other people can rightly say that this technology does not change anything in the need to address inequality, which is already justified for many reasons." In short, the researcher is skeptical about the possibility of changing the opinion of politicians or the public with results such as those of this study, despite their scientific merit.

María Ruz, director of the Mind, Brain and Behavior Research Center at the University of Granada, praises that the study has included a large number of participants, but believes that the interpretation of the results is not simple. "That a greater or lesser cortical thickness is associated with some type of damage does not seem right to me," he says. "In the hippocampus, which they talk about in the introduction, variation in size has been seen due to stress, but they do not see the effect in the hippocampus," he explains. "One thing I think they do very well is make it clear that the brain is plastic and changes with sociocultural variables. But the association between brain regions and mental functions is much more complex than people realize." "The areas they find have been associated with the functions they mention, but also with many others, and a greater or lesser thickness in that region of the brain is not necessarily something negative," he concludes.

Despite the importance of recognizing how the brain explains human behavior, experts also warn of the mistake of using apparently objective measures of an organ – about which much is still unknown – to draw excessive social or political conclusions. The authors themselves point to the need for new studies, such as some that look at human groups whose levels of inequality have varied over time to begin to understand the reasons for the differences observed.

You can follow EL PAÍS Salud y Bienestar on Facebook, Twitter and Instagram.