Preliminary Study Suggests Sex and Gender Map Differently in Children's Brains
More research is needed, but it's worth discussing.
Hiya!
As technology advances, so does science. These days, nearly every scientific field is bursting with discoveries, but perhaps the most exciting discoveries involve ourselves — our history, ingenuity, and biology. Our brains and how they work are of significant interest, particularly how sex and gender affect them.
Sex and gender have become common topics in global conversation over the last few years — and a cultural war within the United States — but they’ve also gained attention in scientific research.
Already, scientists have discovered that transgender people are simply another beautiful variety of human. And today’s topic provides evidence that sex and gender are associated with distinct brain networks in children.
Sex vs Gender, What’s the Difference?
I found some fantastic resources explaining the differences between sex and gender — especially this one by the United States National Institute of Health (NIH, which also funded the study I’ll tell you about soon) and this one by the Council of Europe (COE), Europe’s leading human rights organization. I encourage you to check them out after reading this article to learn more, but for the sake of space, I’m gonna generalize a smidge.
Broadly speaking, a person’s sex (whether they are labeled male, female, or intersex at birth) is determined by various biological differences such as genitalia, chromosomes, hormones, genes, and more. Meanwhile, gender refers to cultural ideas about what it means to be a man, woman, or nonbinary person, which influences how a person presents themselves to society.
Both, sex and gender, shape people’s lives and behaviors, but how do they affect our brains? Is there such a thing as a male or female, or boy/man or girl/woman brain?
Previous research indicates that sex affects someone’s risk of developing various brain-related conditions. For instance, people assigned male at birth (AMAB) are more commonly diagnosed with Attention-deficit/hyperactivity disorder (ADHD), while people assigned female at birth (AFAB) are more likely to experience symptoms of anxiety.
Yet, scientists remain unsure whether sex is driving these differences or if they have more to do with how people are perceived and treated by their society based on their sex or gender.
Scientists understand that sex and gender are related yet distinct concepts — but like many other humans, they, too, often use the terms interchangeably during research. This means that any research showing differences in the brains of people assigned either male or female at birth is assumed to reflect biological differences in the brain when they could result from cultural gender expectations.
Lara M. Wierenga, a neuroscientist who studies gender differences in brain development at Leiden University in the Netherlands, told Allison Parshall of Scientific American that neuroscience research ignores the influence “of being treated as a woman or as a man in our society.”
Similarly, Sheila Shanmugan, a reproductive psychiatrist at the University of Pennsylvania, told Phie Jacobs of Science that sex and gender-based differences in the brain “have historically been understudied, and terms describing each are often conflated.”
Lucina Uddin, a professor of psychiatry and biobehavioral sciences at the Semel Institute for Neuroscience and Human Behavior at the University of California, Los Angeles, told Jacobs that many previous studies “just never bothered to ask about gender.”
But that’s changing with new research led by Elvisha Dhamala, a neuroscientist at the Feinstein Institutes for Medical Research and the Zucker Hillside Hospital in New York State. Dhamala told Jacobs it’s crucial to study the differences between sex and gender because they are “essential components of identity.” She explains:
“It’s becoming more and more clear that just looking at sex itself is not enough. It’s not going to give us all the answers.”
But Dehamala’s new research is an essential first step toward uncovering the answers by discovering differences between how sex and gender are mapped in children's brains.
New Research
For the study, published in Science Advances on July 12, 2024, Dhamala’s team sought to disentangle the effects of sex on brain activity from those of gender.
To do so, the team analyzed data collected as part of the Adolescent Brain Cognitive Development (ABCD) Study, the most extensive, long-term study of brain development and child health in the United States.
The data included functional magnetic resonance imaging (fMRI) scans of 4,727 children (2,315 were AFAB and 2,442 were AMAB), all of whom were 9- or 10-year-olds.
The scans showed the children’s “resting state” brain activity, which happens when we’re awake but not engaged with a specific task. During the fMRI scans, the children also performed tasks related to emotional processing and memory to see how various brain regions and networks communicate.
Data on gender was a little more challenging to collect, as gender differences in the brain are less studied, but the ABCD Study took a nuanced approach. Uddin, who is also the ABCD Study’s justice, equity, diversity, and inclusion associate director, explained to Jacobs that each child participant was asked four questions regarding their gender, such as whether they felt satisfied with the gender assigned to them at birth.
However, since 9-and-10-year-olds may not have a fully developed sense of their own gender identity, the children’s parents were asked twelve questions about various behaviors their child displays and signs of gender dysphoria. For instance, the parents were asked whether they’ve noticed their AMAB child imitating female TV characters or if their AFAB child expresses consistent wishes to be a boy or man.
Then, the researchers used computer algorithms to read and compare the data. The team expected to see sex-related differences in brain activity within specific networks, but beyond that, Dhamala told Parshall:
“[W]e had no idea whether or not [gender] would map onto the brain and also no idea where it would map onto the brain.”
Method
Dhamala and her colleagues’ study had three primary steps.
First, the researchers uploaded the brain scan data and information about each participant’s sex to a machine-learning model designed to identify subtle differences in brain activity between the AMAB and AFAB groups. Then, they asked the model to predict participants’ sex based on data it had not seen yet, which yielded a 77 percent success rate.
After that, the team used a different machine-learning model designed to predict the children’s gender using the children's and their parents' reports. However, since gender and sex are strongly related, many of the brain networks associated with sex and gender overlap.
To get a clearer image, the researchers analyzed the preteens’ gender variation by sex. Separating the scans by sex showed where and how brain activity differed between people who were assigned the same sex at birth but had varying expressions and feelings about their gender.
Lastly, the team compared the networks associated with sex differences with those associated with gender differences. They discovered some overlap, especially with the participants’ self-reports, but a statistically significant difference between the two groups’ brain networks appeared when using the parent-reported gender data. The researchers believe this is because the parent’s questionnaire, which included three times more questions than the children’s, provided more details.
Results
When excluding the overlap in brain networks between sex and gender, the team discovered that the brain networks unique to sex included the nervous system and the visual, emotional, and motor networks. Meanwhile, the networks unique to gender differences were more widely dispersed throughout the brain but tended to involve cognitive abilities like emotional processing, attention, and social cognition. The researchers summarize in the study:
[W]e determine that although there is some overlap in the associations, sex and gender are uniquely represented in the brain.
As promising as the study results are, Dhamala told Parshall that it’s too early to draw sweeping conclusions about why certain brain networks were associated with gender but not sex and vis versa. Right now, she said, “We have no idea” whether these differences relate to any behavioral differences.
Why it Matters
While Dhamala and her team’s study is an early but pivotal step in research regarding gender differences in the brain, they argue their findings suggest sex and gender need to be considered separately in future biomedical research.
Uddin, of the ABCD Study, told Jacobs it’s possible that splitting study participants by sex might lead researchers to overlook the influence of other variables, like gender, on human health and behavior. She said knowing that sex and gender influence the brain differently “could change the way we do science.”
Wierenga, who was not involved in the study, also believes Dhamala’s research hints at major changes in research methods to come. She explained to Parshall the study shows,
“The expectations we have [based on gender], they do matter.”
“This is really the first time that it’s shown in such a large dataset that not only sex but also gender is related to the way the brain is wired.”
Beyond the cool factor that gender has distinct representation in the brain, this knowledge could help us understand how psychiatric disorders manifest across the gender spectrum.
Future Research
As Dhamala said, it’s still early days, and more research is needed, but she and other scientists already have big plans. A starting point is to expand the research to include adults to see whether gender maps differently than sex in the brains of adults.
Dhamala and her team already plan to repeat their methods on the same group of children as they grow up. She explains to Parshall:
“These are still very young kids. And as they go through adolescence and into adulthood, their brain networks and their functional connectivity is going to be changing.”
It’s possible the mapping between gender and sex on the brain changes during puberty, though, Wierenga told Parshall she expects the pattern to hold as we age. As scientists include gender, in addition to sex, in their research, a clearer image of the differences between them in the brain can be revealed.
Cultural norms regarding gender are another factor researchers hope to study since gender norms vary broadly across cultures. Plus, the ABCD Study includes only children in the United States, so it and Dhamala’s study do not reflect the global population.
Proceed with Caution
There are many reasons research regarding sex and/or gender differences in the brain isn’t widely discussed or even conducted, but a significant one is that any findings risk being misinterpreted or exaggerated — And one look at history shows how dangerous such twisting of the truth can be.
For instance, scientists in the 1800s argued women were less intelligent (to put it nicely) than men because women’s brains weigh less on average.
Unfortunately, bias hadn’t changed much by 2003 when clinical psychologist Simon Baron-Cohen (who is also the director of the Autism Research Centre at Cambridge University and author of The Essential Difference: Men, Women and the Extreme Male Brain) argued that women’s brains are hard-wired for empathy and that men are naturally better at understanding and building systems.
Tobias Kaufmann, a neuroscientist at the University of Tübingen and the University of Oslo who wasn’t involved in Dhamala’s research, explains to Jacobs:
“Taken out of context or put in the wrong light, results can easily be used to support or to diminish viewpoints, or to stigmatize.”
Dhamala told Jacobs the best way to avoid such misconceptions is to invite transgender and gender-nonconforming people into the process as both collaborators and participants. She makes the point that:
“You can’t necessarily do research on a population, if you’re not including that population in your research team.”
Such research and collaboration would be highly valuable because many people belonging to these communities have traditionally been underrepresented and treated as abnormal by scientists, but they have unique insights into the nature of sex and gender that are well worth listening to.
Perspective Shift
Now, more than any other point in history, we’re more equipped to investigate some of humanity’s biggest questions that have remained beyond our reach. But we can also re-investigate long-held ideas to see if they’re correct. In this case, sex and gender, long assumed to be one and the same, are actually two distinct concepts, each with a unique representation in the brain.
Granted, the research is new, and it takes time for (factual) information to spread. Still, it’s a significant step toward better understanding ourselves as a species and should be celebrated. This research also supports two related themes I keep noticing in the new research I’ve read since starting this newsletter — that everything is a spectrum and diversity is powerful.
P.S. Don’t forget to scroll back up and check out the two resources by the NIH and COE to learn more about the differences between sex and gender!
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Thank you for reading. I appreciate you!
Yes, it’s important to remember that everything is on a spectrum. It’s not as easy to deal with as simply declaring something black or white, but imo it’s the more humane, intelligent, and enlightened way.