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New Study Suggests Structural Brain Differences in Transgender Women

Brazilian researchers have found variations in the volume of the insula, a brain region associated with body image.

The researchers from the University of São Paulo's Medical School (FM-USP), used magnetic resonance imaging (MRI) technology in what is the first Latin American study to investigate brain volumes in transgender people.

The team performed a structural analysis to find differences in gray and white matter volume based on the results of their scans. The study included 80 individuals between the ages of 18 and 49 years old. They were divided into four distinct groups of 20 people; cisgender women, cisgender men, transgender women who had never used hormones, and transgender women who have used hormones for a period of one year or more.

The results showed that the volume of the brain region called the insula was smaller in both hemispheres for both groups of transgender women. The insula plays an important role in self-awareness and body image. Other functions such as utonomic control, homeostatic information and visceral sensations are also processed within the central nervous system by the insula. The size of the insula was not smaller in transgender women when compared to cisgender men, but its volume was reduced in transgender women when compared to cisgender women.

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

The researches were also careful to point out that that reduced gray matter volume in a brain region does not necessarily mean the region in question contains fewer nerve cells.

“The various gray matter brain regions contain a mass of synapses and nerve endings (called neuropils) that can change volume dynamically,” said Professor Geraldo Busatto, who heads the Psychiatric Neuroimaging Laboratory (LIM21) at FM-USP’s general and teaching hospital (Hospital das Clínicas) and who was an associate researcher in the study. “For example, at any time during one’s life, a brain region’s density may increase owing to more activity, leading to a subtle rise in the volume of local gray matter.”

Image Source: Scientific Reports - Nature.com

There have been previous studies that have found that sexual differentiation of the brain in transgender individuals does not accompany differentiation in the rest of the body. “The first studies with images of the brains of transgender individuals looked for structures, regions or even functional parts of the brain that most resembled those of people of the gender with which those individuals identified, said Spizzirri . “We found that trans people have characteristics that bring them closer to the gender with which they identify and [that] their brains have particularities, suggesting that the differences begin to occur during gestation.”

What the study shows is that being transgender is not just a behavior that a person can develop, and that it is not simply an ideology. There is a structural basis in human development. “We observed specificities in the brains of trans individuals, an important finding in light of the idea of gender ideology,” said Carmita Abdo, coordinator of the Sexuality Research Program (ProSex) at the Psychiatry Institute of Hospital das Clínicas, and principal investigator of the study. “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.”

Geraldo Busatto also cautioned that the findings couldn’t be seen as indicating specificity. The insula is a region with multiple elements,” Busatto said “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, and in addition, they unfortunately suffer discrimination and persecution,” Busatto also said.

The authors of the study have hypothesized that these findings may be a characteristic of trans women. They also concluded that reduced insula volumes could not be explained by hormone treatment.

“We hope this study will be replicated with larger samples, but right now, it can be said that the hypothesis of transgender development is supported and merits investigation,” Abdo said.

The researchers are hoping to conduct further studies in the future focused on determining the stage of development in which differences occur. “Having detected these differences, we should try to find out when they begin to emerge,“ Abdo also said. “Among other points, it would be interesting to study [the] brain scans of children and young adults with transgender characteristics and compare them with the scans of adult trans women.”

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