Differences between the brains of women and men appear to be more pronounced in countries where there is greater social inequality between the sexes. Brain scans of nearly 8,000 people from 29 countries reveal that parts of the cortex are thinner in women than in men in countries where they are socially disadvantaged. In contrast, in countries with more equality, there were no significant gender-related differences in cortical thickness. The results suggest a possible link between gender injustice and an increased risk of mental health problems and underachievement in school.
In many countries around the world, women face discrimination in a wide range of areas, such as education, the workplace, political representation and health care. This inequality between the sexes is measured using indices such as the Gender Gap Index of the World Economic Forum and the Gender Inequality Index of the United Nations. Previous studies have found that women in countries with high gender inequality are at higher risk of mental illness and have lower levels of education than men.
deprivation in the brain
But do such differences also appear in the brain? A team led by André Zugman from the American National Institutes of Health (NIH) in Bethesda investigated this question. To do this, the team evaluated brain scans of people from 29 countries around the world – around 4,000 each from women and men. The sample included both countries with large gender gaps, such as India, Brazil and Turkey, and countries where the indices show women and men to be equal in many areas, such as Finland, Sweden, Germany and Spain. Around 35 percent of those included came from low- and middle-income countries.
The result: "In countries with greater gender inequality, there were clear gender-specific differences in the brain, with the cerebral cortex in the right hemisphere being thicker in men than in women," report Zugman and his team. "In contrast, in countries with greater gender equality, there were virtually no differences in cortical thickness between the sexes." In some cases, the cerebral cortex was even thicker in women than in men. While the thickness of the cerebral cortex did not differ systematically in men from different countries, the differences were due to the fact that women from countries where they are particularly disadvantaged had a smaller cortical thickness.
Social stress and poor educational opportunities
Brain regions affected by the differences included the anterior cingulate gyrus and the orbitofrontal gyrus. "These regions are associated with various aspects of emotional control, including resilience to adversity, responses to injustice, or negative social comparisons," the research team explains. "Changes in these regions were also found in pathological conditions in which stress is considered a central mechanism, such as a thinning in depression or a reduction in volume in post-traumatic stress disorder." It is therefore conceivable that the thinner cerebral cortex in women from countries with large gender differences stems from the fact that they are exposed to unfavorable conditions and thus stress throughout their lives.
From the researchers' point of view, other mechanisms are also possible: "Women in the respective countries have less access to a beneficial, enriching environment that could positively change their brain structure through stronger dendritic branching and increased synapse formation." Access to the education system is important. "Our study could not further investigate which of these mechanisms were involved because many types of negative experiences coexist," the team said.
"Our results underscore the importance of the macrosocial environment in which gender differences in brain structure manifest themselves," Zugman and his team write. "Future studies need to examine the mechanisms involved, their moderating factors and their timing, offering new opportunities for neuroscience-based policies to advance gender equality."
Source: André Zugman (National Institutes of Health, Bethesda, USA) et al., Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2218782120