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Study finds differences in the brains of men and women, but only in countries with the greatest gender inequality

The analysis of almost 8,000 MRIs from 29 nations suggests that a harmful social environment alters the structure of the brain

India
Among the countries that were studied, India is the one with the greatest inequality between men and women.Sudipta Das (NurPhoto via Getty Images)

Many studies have shown that in countries with higher gender inequality, women are more at risk of suffering from mental illnesses and tend to have less academic success than men. A person’s brain, like the amount of belly fat or the strength of the muscles, is altered by the circumstances of the environment; however, these transformations are sometimes not so evident, as they are hidden by the skull. In China, for example, it has been observed that dementia is higher among women, and lack of exercise and illiteracy have been identified as risk factors for this type of disease.

To test whether the circumstances of greater or less inequality between the sexes are related to the 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 by the PNAS magazine, they explain that in the nations with greater gender equality – measured with the Gender Inequality Index and the Gender Gap Index – no significant differences were observed between the male and female brains. However, where the gender imbalance was higher, they found that the cortical thickness of the right hemisphere was thinner in women.

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

Nicolás Crossley, a professor at the Pontifical Catholic University of Chile and co-author of the study, explains that this type of work points to an observable effect of gender inequality in the brains of people who are exposed to permanent subordination and even physical violence. Although the study does not establish a causal relationship, and despite the fact that “these results are not necessary to make the case that gender inequality is wrong,” he believes that this can lend weight to the 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 we show, in some way, that there is real damage caused by gender inequality,” he assures.

The origin of the differences

For Crossley, these results could also affect the notions about the origin of the differences between men and women found in societies around the world. “There are people who argue that the differences in social roles are the result of biological differences, and here we show that some of those differences can be changed by the social environment.” In addition to influencing the way of seeing the origin of the inequalities, the authors, with a phrase that has been questioned by some colleagues who did not participate in the study, state that their results “provide initial evidence for neuroscience-informed policies for gender equality.” According to the Chilean researcher, the ability to measure brain alterations and link them to changes in gender policies can be used to “monitor how certain public interventions are reflected in these brain measurements or tell us at what critical moments in the development of a person it is more important to apply public policies.”

A person undergoes a brain scan.
A person undergoes a brain scan.Nolan Zunk/Universidad de Texas en Austin

Bruce Wexler, a professor at Yale University, believes that “what would have been more surprising would have been if the researchers had not found any differences in the brains of men and women where women have much less intellectually stimulating jobs, have little access to education or are not encouraged to perform 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 the structure of the brain,” explains Wexler, author of the book Brain and Culture, where he explores the synergies between human neuroplasticity and the fact that humans alter their environment, which in turn, alters their brains.

Wexler questions whether the authors’ claim about the value of their results to promote equality policies will hold up. He believes that “although MRIs, due to their ability to measure the brain, can impress some people and move them to act, others can rightly say that this technology changes nothing in the need to confront 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 like those of this study, despite their scientific merit.

María Ruz, director of the Mind, Brain and Behavior Research Center at the University of Granada, in Spain, commends the fact that the study included a large number of participants, but believes that interpreting the results is not easy. “That a greater or lesser cortical thickness is associated with some type of damage does not seem right to me,” she says. “In the hippocampus, which they talk about in the abstract, a variation in size due to stress has been seen, but they don’t see the effect on the hippocampus,” she explains. “One thing that I think they do very well is make it clear that the brain is plastic and changes with socio-cultural variables. But the association between brain regions and mental functions is much more complex than people think,” she points out. “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 a negative thing,” she concludes.

Despite the importance of recognizing how the brain explains human behavior, experts also warn against using seemingly objective measures of an organ — one about which much is still unknown — to draw disproportionate social or political conclusions. The authors themselves are aware of the need for new studies, like some that observe human groups whose levels of inequality have changed over time, in order to begin to understand the reasons for the differences observed.

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