Research on the differences between men’s and women’s brains is plentiful, but not entirely conclusive. Now a new study identifies notable variations between the brains of the two sexes, as well as distinct variations based on a person’s gender.
A team of researchers from the United States and Singapore analyzed brain activity via fMRI scans in 4,757 children aged 9 or 10: 2,442 assigned boys at birth (AMAB) and 2,315 assigned girls at birth (AFAB), who had participated in the Adolescent Brain Cognitive Development (ABCD) study.
These data were cross-referenced with responses given by children about their feelings about their gender and responses given by their parents about the child’s behavior, including signs of gender dysphoria – not feeling aligned with the sex assigned at birth.
“Here, we use the term ‘sex’ to indicate characteristics of an individual’s physical anatomy, physiology, genetics, and/or hormones at birth, and we use the term ‘gender’ to indicate characteristics of an individual’s attitude, feelings, and behaviors,” writes the team led by neuroscientist Elvisha Dhamala of the Feinstein Institutes for Medical Research in New York.
“Gender is not binary. However, in the ABCD sample analyzed here, all participants reported their gender as either female Or male” . “
Using machine learning algorithms, the researchers identified significant differences in brain connectivity based on sex, as well as more subtle differences in brain connectivity related to gender. It is essential to distinguish between sex-based variations and gender-based variations.
It’s important to understand that this doesn’t mean that male and female brains are wired differently from birth; it means that certain brain activity in these scans, in networks related to movement, vision, and emotion, is a good indicator of whether a brain is male or female.
And while gender predictors are less reliable and less well-defined, they are correlated with those related to a person’s sex, but they are also different from sex-based predictors and they are more distributed in the brain.
“Sex and gender have traditionally been conflated in research when they should have been studied separately,” says Dhamala.
This distinction stems from how our biology, including our genes and hormones, and our environment, including our social experiences, influence the brain. Because our brains are so malleable, our internal experiences and how others treat us can influence our gender.
There are major implications here. For example, certain conditions such as ADHD (attention deficit hyperactivity disorder) and Parkinson’s disease are more commonly diagnosed in people with AMAB, while anxiety and Alzheimer’s disease are more likely to be diagnosed in people with AFAB.
Gender could influence this bias, as could sex, and in more profound ways than one might think.
“Women, AFAB individuals, and sexual/gender minorities have historically been excluded from biomedical research. As a result, this group of individuals is more likely to be underdiagnosed or misdiagnosed for common brain disorders,” the researchers write.
“Collectively, these findings suggest that both sex and gender are associated with individual functional connectivity and that these associations may underlie the sex and gender differences that exist in brain-related diseases.”
The study authors acknowledge a major limitation to their work: The people involved in the research have not yet reached puberty, a crucial period for gender identity and feelings surrounding it. The results may well be different in older groups.
Given the considerable influence of culture on gender, more research is needed across a wider range of people from different countries and ethnic groups. In the meantime, it might be time to revisit brain studies.
“This research highlights the complex and nuanced ways in which biological and environmental factors influence brain organization,” Dhamala says, “and shows the need to consider a person’s sex and gender to fully understand health and disease across the human lifespan.”
The research was published in Scientific progress.
