Approximately 1.4 million Americans are transgender. Despite scientific evidence to the contrary, polling demonstrates that 21 percent of Americans think that this population has a mental illness, and 39 percent think being transgender is a choice. Science repeatedly refutes these views, and new research presented at the annual meeting of the European Society of Endocrinology on Tuesday shows even further evidence that transgenderism has biological roots.

In the presentation in Barcelona, Spain, University of Liège researcher Julie Bakker, Ph.D. explained that the brain structure and activity of transgender adolescents more closely matches up with the gender they identify with, not the one they were assigned at birth.

The fact that young transgender people have identifiable brain activation patterns suggests that someday, as Bakker and her colleagues hope, brain imaging could be used as a tool to identify people who are transgender early in their lives. Earlier identification, she says, could help mitigate the experience of gender dysphoria — the unsettling and often distressing experience of knowing your assigned gender is not your identity. Currently, the majority of transgender adolescents are put into psychotherapy or are given hormones to delay their puberty in order to push back their choice to physically transition until they’re older.

“The earlier one can start with the treatment, including puberty inhibition with GnRH agonists then followed by cross-sex hormones, the better the outcome,” Bakker tells Inverse. “Often they [transgender adolescents] have to wait a long time, and they develop the secondary sex characteristics of their biological sex. This is of course very difficult for them psychologically speaking.”

Trans Solidarity Rally
Marchers at the 2015 Trans Solidarity Rally in Washington, D.C.

Through two experiments, the team characterized the brain activation patterns of 160 young transgender people with gender dysphoria. In the first, they assessed the brains of male- and female-identifying transgender adolescents using an MRI scanner. Before their brains were scanned, the individuals were exposed to a pheromone called androstadienone, a “male modulator chemo-signal” that induces gender-specific brain activity, as Bakker found in a previous study. Smelling it induces a response in the hypothalamus (a region critical for reproduction) of heterosexual, cis-gender women, but not in heterosexual, cis-gender men.

The MRI scans showed that the hypothalamic responses of both the adolescent transgender girls and boys were more similar to their experienced gender than their birth sex, which, the team writes, “supports the hypothesis of a sex-typical brain differentiation of these individuals.”

At the structural level, they also found that that the regional gray matter and white matter volumes of the individual’s brains also deviated from the characteristics of their assigned sex. Instead, their brains were more similar to the cis-gender adolescents who share their gender identity.

In the second experiment, adolescents whose assigned sex was female but identified as males demonstrated a male-typical brain activation pattern during a visual and spatial memory exercise called mental rotation. During this exercise, individuals have to imagine and state what a stimulus would look like if it was rotated. Bakker says that, “We know that men are generally better than women at performing this task, but even if you take groups of men and women who perform equally, different brain regions will be activated in men versus women because they use different strategies to solve this task.”

hypothalamus
The hypothalamus is circled.

This research joins previous studies showing that the structure and composition of the brains of transgender individuals more closely resembles the brains of the gender with which they identify, regardless of whether they have begun hormone treatment. For people who question the validity of their identity, this growing body of research may be quite affirming.

The work, however, only accounts for a binary interpretation of transgenderism. Being transgender doesn’t necessarily limit gender identity to being “male” or “female,” and individuals may not feel exclusively either way. To rely on biomarkers is potentially problematic as well: What if a transgender person’s brain doesn’t “match” what scientists are looking for?

Still, it’s Bakker’s intention for this research to help the transgender community. Sex differences in the brain, she asserts, are real — even if there are more similarities than differences. Accepting that will not only create better procedures for general research (findings on male brains, she notes, are often inaccurately extrapolated to women) but can create a better society overall.

“There is still some resistance in different groups,” says Bakker. “I hope that this kind of research will help the acceptance of people who are a bit ‘different’ than the norm.”