While magnetic resonance imaging (MRI) has been used to study sex differences by observing the structure of the brain, the morphology has rarely been explored in transgender women (i.e. assigned male at birth) diagnosed with gender dysphoria.

In a recent study, researchers from the Medical School of the University of São Paulo, Brazil, decided to investigate this by recruiting 80 participants between the ages of 18 and 49 years. They were categorized into four groups of 20 members each: cisgender women, cisgender men, transgender women who had never used hormones, and transgender women who had used hormones for at least a year. MRI scans were then used to look for differences in gray and white matter volume of the brains.

It was revealed that both groups of transgender women had variations in the volume of the insula in both hemispheres. The insula is a region of the brain that reads the physiological state of the body, thus being responsible for body image and self-awareness. 

"It would be simplistic to make a direct link with transgender, but the detection of a difference in the insula is relevant since trans people have many issues relating to their perception of their own body because they don't identify with the sex assigned at birth," said Professor Geraldo Busatto, a researcher in the study. In addition to the internal struggle, he adds a reminder that transgender individuals may end up suffering discrimination and persecution.

Busatto heads the Psychiatric Neuroimaging Laboratory at the general and teaching hospital (Hospital das Clínicas) at the University of São Paulo. He stresses that the insular region is associated with multiple elements and cannot yet be used as a basis for specific differences.

Giancarlo Spizzirri, the first author of the study, highlights the fact that transgender people do display structural variations and characteristics that bring them closer to the gender with which they identify. Evidence of particularities in their brain also suggests the differences may begin to occur during gestation.

Carmita Abdo, a principal investigator of the study, calls it an important finding with regards to gender ideology. "The evidence is building up that it's not a matter of ideology. Our own research based on MRI scans points to a detectable structural basis," she said. 

As both transgender groups displayed a variation of the insula volume, the study stated this could be a characteristic of transgender women. This particular feature failed to be explained by the use of or the lack of hormone treatment, the study concluded.

"It’s important to recall that there’s no such thing as a typically female or male brain. There are slight structural differences, which are far more subtle than the difference in genitals, for example. Brain structures vary greatly among individuals," Spizzirri said.

The researchers hope this study can be replicated in larger samples, with more attention directed towards detecting when the brain differences begin to emerge. One method suggested by the authors is to compare brain scans of children or young adults who have transgender characteristics and compare them to scans of adult transgender women.

The study "Grey and white matter volumes either in treatment-naïve or hormone-treated transgender women: a voxel-based morphometry study" was published on January 2018 in Scientific Reports.