Most brain imaging studies involving transgender people or people with gender dysphoria have focused on whether their brains look more like what’s typical for the gender they identify with, rather than the gender they were assigned at birth based on their biological sex. For example, whether trans men have “masculine” brains, and trans women have more “feminine” brains.
A new study in Brain Imaging and Behaviour adds to this trend, showing that trans men have unusual patterns of connectivity in brain networks involved in processing of the self, as compared with male and female controls. “The present data do not support the hypothesis that sexual differentiation of the brain of individuals with gender dysphoria is in the opposite direction as their sex assigned at birth,” the researchers said, adding that the unusual connectivity patterns they found in trans men “was detected in comparison with both male and female controls, and there were no differences between the control groups”.
The research team led by Jamie Feusner at University of California, Los Angeles, scanned the brains of 27 trans men (whom they refer to as female-to-male persons with gender dysphoria) recruited via a gender dysphoria clinic at the Karolinska Institute in Sweden where they’d been diagnosed with gender dysphoria, specifically transsexualism (according to ICD 10 criteria). The trans men had not yet undertaken the surgery and/or hormone treatment that they were seeking; they had no other current psychiatric or neurological diagnoses. There were also 27 male and 27 female cisgender controls.
This was a resting-state brain scan, so the participants simply lay in the scanner doing nothing. The researchers then analysed the participants’ patterns of neural activity at rest to look for signs of connectivity in various brain networks, including the “default mode network” (which is more active when we’re mind-wandering and thinking about the self rather than engaged with the outside world) and the “salience network” which processes internal bodily sensations, among other things.
Eighteen of the trans participants and some of the controls also completed a body morph test (see example photographs above): they looked at images of their own body, shown for either half a second or two seconds, that were morphed to varying degrees with the body of another man or woman, and they had to say to what degree the photo was of themselves.
The trans men showed weak connectivity in areas of the default mode network as compared with both the male and female controls. As you’d expect, they were also more likely to rate the body morph photos as being themselves when they were morphed with a man’s body, rather than a woman’s or unmorphed. Moreover, at longer viewing times, this identification with a masculinised version of their own body correlated with greater connectivity within pregenual anterior cingulate cortex – part of the default mode network that’s associated with feelings of self. The controls didn’t show this correlation, but at shorter viewing times they (but not the trans participants) showed a correlation between seeing their unmorphed body as their own and connectivity within the right insula – a region involved in the rapid processing of internal bodily signals.
The interpretation of these different brain activity patterns is highly speculative but the researchers said the results are consistent with the idea that in trans men “higher cortical systems” were modulating the activity of more reflex systems involved in self and own body processing. The researchers said: “Gender dysphoria individuals differ from controls with respect to connectivity within networks involved in self-directed thinking and that relate to own-body identification, which could represent a neurobiological correlate of their condition.”
Whether these unusual brain activity patterns play a role in causing gender dysphoria or are the consequence of it, or both, is not clear. It also remains to be seen how surgical or hormone treatment might interact with these neural patterns. More research, especially longitudinal that tests participants over time, is needed to tease out cause and effect; and research with trans women is also required to see if the current findings generalise.
Image: taken from Feusner at al, 2017 shows stimuli from the body morph task.