Children’s brains may show how sex and gender are different, study says

Sex and gender are often confused or equated in everyday conversation, and most American adults believe that a person’s gender is determined by the sex assigned at birth. But a new study of nearly 5,000 9- and 10-year-olds finds that sex and gender map widely distinct parts of the brain .

The research provides the first insight into how sex and gender may have “measurable and unique influences” on the brain, the study authors said, just as other experiences have been shown to shape the brain.

“Moving forward, we really need to consider both sexes and genders separately if we want to better understand the brain,” said Dr. Elvisha Dhamala, an assistant professor of psychiatry at the Feinstein Institutes for Medical Research and Zucker Hillside Hospital in Glen Oaks, California, and co-author of the study, published Friday (12) in the journal Science Advances.

The researchers in the new study defined sex as the sex assigned to a child at birth. In the U.S., clinicians make this assignment based on genitalia. Most people are assigned sex woman or man according to the survey; the rest is intersex a person whose sexual or reproductive anatomy does not fit into this male/female binary.

Researchers defined gender as an individual’s attitudes, feelings, and behaviors, as well as socially constructed roles. They specifically noted that gender is not binary which means that not all people identify as female or male.

Both sex and gender are an essential part of the human experience. They are central to how people perceive others and how they understand themselves. Both can influence behavior as well as health, the study authors say.

Researchers analyzed brain imaging data from 4,757 children in the United States, 2,315 assigned as girls at birth and 2,442 assigned as boys at birth, who were ages 9 and 10 and were a subset of the Adolescent Brain Cognitive Development (ABCD) study, the largest long-term study of brain development and child health in the United States. Over a 10-year period, children in the ABCD study underwent comprehensive neuroimaging, behavioral, developmental and psychiatric evaluations.

In addition to tests such as MRIs, the scientists conducted gender-focused surveys of the children and their parents both at the beginning of the study and a year later. The children were asked about how they expressed their gender and how they felt about it. The parents were asked about the child’s gender-specific behavior during play and whether the child had any gender dysphoria, a term mental health professionals use to describe clinically significant distress felt because a person’s sense of gender does not match the sex assigned at birth.

You parents were a fundamental part of the study said study co-author Dr. Dani S. Bassett, a professor at the University of Pennsylvania with appointments in the departments of bioengineering, electrical and systems engineering, physics and astronomy, neurology and psychiatry.

“When children have a specific type of gender behavior or gender expression, that will influence how their parents and also other caregivers, friends and family … interact with them,” Bassett said. Information about parents’ perceptions of a child’s gender gives researchers a better sense of a child’s social environment and how that may affect their brain development.

The authors used a type of artificial intelligence called machine learning that built a model that could predict a child’s sex and reported gender from their brain scan. When researchers analyzed the children’s brain scans, the results appeared to show that gender influenced different regions of the brain that are involved in visual processing, sensory processing and motor control, and some regions involved in executive function, which allows an individual to organize and integrate information over time.

Gender appears to influence some of the more specific sensory networks that are associated with sex, but it also appears to have a broader influence and can be detected in different brain networks involved in executive function, including things like attention, social cognition, and emotional processing.

“The fact that we are able to capture how gender maps onto the brain basically tells us that the gender is influencing our brain “, said Dhamala.

A structure of the human brain can be shaped by experience and knowledge . Research on London taxi drivers — who must undergo extensive testing to show they can navigate the city’s streets without maps or GPS — appears to show that they have significantly larger posterior hippocampi, the part of the brain involved in spatial memory and navigation, than people who are not taxi drivers.

“Similarly, as individuals and as humans, we are experts on ourselves and our genders. So it makes sense that gender is also mapped into our brains,” Dhamala said.

What the new study cannot do is predict what gender a person might identify with beyond a time-limited snapshot captured by the scans and surveys. Gender, the authors note, is not necessarily static, and a person’s understanding of their gender can change over the course of a lifetime.

The study also can’t determine what things in someone’s environment will influence their brain function in terms of sex or gender, nor can it identify what a person’s sexual orientation might be. “Sexual orientation is independent of gender and sex,” Bassett said, and may map differently in the brain.

The researchers say they hope to one day learn more about how sex and gender interact in a person’s life and how they influence each other and the brain across the lifespan. They also hope to see how different cultures affect gender of a person and their brain development.

A 2022 poll found that most American adults — and a large majority of conservatives — believe that a person’s gender is determined by the sex they were assigned at birth. The distinction is essential for gender-affirming care, medical treatment for people who identify as a gender different from the one they were assigned at birth. Conservative politicians have pushed for a record number of bans on such care, and nearly half of U.S. states have enacted bans on gender-affirming care for minors.

The study did not look at whether sex or gender were congruent or incongruent in any study participant. Instead, it looked at the child’s binary sex and gender on self-reported and parent-reported measures. The study was unable to provide any specific findings if sex and gender were incongruent.

“Moving forward, the hope is that we can motivate other scientists to consider science and gender in their analyses of data collection in their programs and research,” said study co-author Dr. Avram Holmes, an associate professor of psychiatry at Rutgers University.

The field of neuroscience has only just begun to recognize and address the presence of biases and barriers to inclusion in research, Holmes said.

A more complete understanding of how the brain works in terms of sex and gender could also have practical implications and potentially help scientists find better ways to treat people with brain-related diseases. For example, the study highlighted how people assigned male at birth are more likely to be diagnosed with substance use and attention deficit disorders.

“It’s not that sex and gender necessarily drive disease rates, but the cultures in which people are raised can also influence whether or not they’re likely to develop a particular disease,” Holmes said. “So the types of environmental pressures a child experiences throughout development can increase or decrease their risk of disease, regardless of their early brain biology.”