Differences in the brain’s response to touch may explain why transgender people often feel at odds with their anatomy. Information from studies that show this may one day help doctors better help children who identify as trans.
Many trans people feel that parts of their body don’t fit with their gender identity. Those who have surgery to change their anatomy overwhelmingly say they feel more like themselves afterwards.
To see if the way the brain processes body image underlies feelings of body incongruity in trans individuals, Laura Case at the University of California, San Diego, and her colleagues recruited eight volunteers who were anatomically female but identified as male and strongly desired a male anatomy. Eight biologically female people who identify as women were also recruited as a control group.
Participants were tapped on the hand or the breast while their brain activity was monitored using magnetoencephalography. Each person’s brain was then imaged using MRI, and the team combined this information to get a clearer picture of the neural response to the tapping.
They found that, in both groups, stimulation of the hand and breast caused areas of the secondary somatosensory cortex to buzz with activity – unsurprising, as this part of the brain is involved in the conscious awareness of touch.
But in the trans group, the activity in this area was significantly lower when their breast was touched compared with their hand (Archives of Sexual Behaviour, doi.org/brnj).
There was also less activity in an area called the supramarginal gyrus. This has been implicated in the ability to attribute a sense of “this belongs to me” to our body parts. For example, stimulating an area close to the supramarginal gyrus can elicit out-of-body experiences. The reduced activity in this area seen in the trans volunteers when the breast is touched suggests that the brain may not treat the breast as strongly belonging to the “self”, says Case.
It is difficult to tell whether these brain differences are innate causes of feelings of discomfort towards gendered body parts, or whether a trans person’s aversion to a body part could have caused changes like these to occur in the brain over time.
“[Our experiment] doesn’t tell us why these differences exist, but we hope it adds to the medical understanding of gender identity and the importance that physical transition has to many individuals,” says Case.
Studying children before and during their experiences of gender mismatch may help untangle this, but would be difficult to do, says Case – not least because these body parts are typically private areas, and children may not be very articulate about their gender identity.
Case’s study is one of several that have identified neural differences in trans people. For instance, a previous study discovered significant differences between male and female brains in four regions of white matter – and that female-to-male trans individuals who hadn’t had sex reassignment surgery had white matter in these regions that more closely resembled a male brain.
Based on results like these, Case and her colleagues hypothesise that some female-to-male trans individuals may have an internal body representation that is closer to being anatomically male than female. If this is the case, it would mean that when their breast is touched, it is compared with an internal representation that has no female breasts. This mismatch could mean that the sensation isn’t as well integrated into a person’s sense of feeling, leading to a reduced sense of ownership for that part of the body.
Children as young as 2 can express a strong desire to have body parts of the opposite sex, and it is harder to transition after puberty. But these feelings persist in only around 27 per cent by the time they reach adolescence, making it hard for doctors and psychologists to decide whether to give children drugs that delay puberty, or that cause changes that will make it easier to transition later on. Brain activity may help inform these decisions.
However, although Case’s study is interesting, we still don’t have enough information to identify trans and non-trans brains at the individual level, says Ivanka Berglund at the Karolinska Institute in Stockholm, Sweden. As a result, it isn’t yet possible to use scans to identify whether a child is trans or not, she says.