Scientists from China conducted a study involving 16 transgender women, 16 cisgender men and 16 cisgender women. Transgender women are people who were assigned male sex at birth but identify as women. Cisgender people are those whose gender identity matches the sex assigned at birth. The work was published in the journal Scientific Reports.
Participants' brains were scanned using resting-state functional magnetic resonance imaging (fMRI): the person lies in the scanner and does nothing, while the device records the activity of different regions. The researchers then compared several measures: the strength of spontaneous fluctuations in activity in individual areas, the consistency of activity in neighboring zones, functional connectivity between distant regions (how synchronously their activity changes) and the efficiency of information exchange overall.
It turned out that transgender women, more strongly than both groups of cisgender participants, showed slow spontaneous fluctuations in activity in the cerebellum, precentral gyrus and thalamus - areas associated with movement and the processing of sensory information. In addition, they had lower consistency of activity in neighboring areas in some zones of the precuneus - a region involved in thoughts about oneself.
Transgender women also showed weaker functional connectivity between the ventral attention network (which helps notice unexpected or important stimuli) and the sensorimotor network (which processes sensations and controls movements), as well as within the sensorimotor network itself. Finally, they had lower local efficiency - a measure of how effectively information is transmitted within closely connected groups of brain regions.
On most of these parameters, cisgender men occupied an intermediate position between transgender women and cisgender women. For example, connectivity between the sensorimotor and ventral attention networks was weakest in transgender women, intermediate in cisgender men and highest in cisgender women. The main results persisted after adjustment for overall brain size.
The authors conclude that the brain activity pattern of transgender women differs from that of cisgender people, but is more similar to the pattern of cisgender men (that is, people assigned male sex at birth) than to that of cisgender women. The researchers suggest that differences in sensorimotor areas may be related to how transgender women perceive their own body, but this was not directly tested.
It is important to emphasize: the study does not prove causal relationships, but only describes statistical differences. The sample is very small - 16 people per group - and the scanning was relatively short, which reduces the reliability of the conclusions. Almost all transgender women were receiving hormone therapy, and its influence was not taken into account, so it cannot be said whether the differences are related to hormones or other factors. In addition, transgender men did not participate in the work, and participants' mood was not measured, although depression is more common among transgender women and may affect brain activity.