Men’s and women’s brains

Do trans women have women’s brains, and if so, does it matter? Do trans women think like women?

In the 1990s, I learned about the BSTc, a part of the amygdala which is twice the size in men than in women, slightly larger in gay men, and women’s size in trans women. Problem solved, I thought, trans women have women’s brains. It can only be measured by dissection, though, so is no use as a diagnostic tool, and my internalised transphobia spoke up: what if I don’t? What if that means I am not trans?

Women’s brains have more white matter. White matter connects brain areas with other areas further away. So more white matter means more connectivity. Rather than using a single part of the brain for a particular function, women are more likely to use different parts.

All brains show differences between the left and right side, from nematodes up, and Iain McGilchrist in The Matter with Things explains this is because all animals need to eat without being eaten. The left side pays specific attention to prey, and the right side pays global attention to everything going on, as predators could come from anywhere. The right hemisphere is larger than the left in both sexes, but the effect “seems to be” more marked in males.

“Seems to be”- it seems that McGilchrist does not consider there is enough research to be definite. Lay people will often not know for any common assertion whether it is based on detailed and conclusive research, on one suspect study, or has been debunked. There is more research all the time.

Differences in brain structure might produce different behaviour, but might equally well prevent differences in behaviour by compensating for other sex differences such as the effects of sex hormones. For example, the right frontal cortex is crucial in the empathy between mother and infant, so might be less well adapted to making risk decisions, as it does in the male.

Testosterone in utero makes the right hemisphere grow faster in males than females, by inhibiting left hemisphere growth. But the same level of testosterone in males and females will have differing effects, and women may use different parts of the brain for particular tasks depending on whether they take contraceptives, or where they are in the menstrual cycle. I know from taking synthetic progesterone the effect it had on me.

I don’t know that I have any particular androgen insensitivity, though once I started on testosterone blockers my T levels dropped. I don’t know what might lead doctors to check. So my brain development in the womb was probably fairly male-typical, just as my development of sexual characteristics elsewhere in the body was. An AI shown enough brain scans of trans people can discern whether other scans are of trans or cis, but that only means there are recognisable differences in the brains of trans people, not that trans women have “women’s brains”.

Researchers can find what areas of the brain perform what tasks by studies of people with brain injury, or by brain scans. Differences in which hemisphere performs a task may be missed if researchers use equal numbers of men and women.

In a study of musicians, the compositions that had the highest ratings were by composers with a brain difference which all the men, and only some of the women, had. So the dominance of men in the culturally recognised history of great composers may be in part physical, though it is also Patriarchal.

Females have greater verbal facility, and males better visuo-spatial skills. Women use words to think through a nonverbal task. Ah, I think, I have no mind’s eye, and great verbal facility. But that does not by itself make me a woman.

If I tried totting up the ways where I was more like a woman, I would be guilty of sexist assumptions as well as proven differences, and my internalised transphobia might never think the list I came up with was sufficient, even now. What makes me a woman is my ineradicable conviction that I want to express myself this way, like trans people have in all cultures for millennia. I don’t believe in a soul, or even a mind separate from the effects of neurons, so that conviction is the effect of my physical brain.

I am a woman, therefore I have a woman’s brain, even if its sex differences are not the same as cis women’s.

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