Your brain doesn't care what genitals you have

The concept of a sexually dimorphic brain has been a popular concept over many centuries, including as part of the nature-versus-nurture debate and related, such as when trying to explain the far higher rate of men committing (and becoming the victim of) crimes [1]. For the latter the current statistical trend shows that this big difference is becoming ever smaller. Much like with things such as cigarette smoking, it appears that social factors are mostly behind such differences, and not anything innate.

This is supported by recent research on whether there are any characteristics in the human brain that would allow us to differentiate brains into a 'male' or 'female' category [2]. The executive summary is that there is no such thing. As the PNAS study points out, human brains are mosaics of features and characteristics, with some more pronounced or formed in a particular way, but as a whole human brains are incredibly diverse.

While one could argue that some structures in the brain are more readily formed when, for example, specific (hormonal) triggers are present during brain development, and there is definitely sufficient evidence that shows that the development of the brain before birth is affected by a myriad of external factors, the human brain is essentially unisex.


This poses the interesting question of how this lack of dimorphism translates into the often used phrases about 'feeling like a woman', or 'feeling like a man'. Here, too, the social component appears to be responsible [3], with a 'gender social contract' or GSC forming an essential part of most societies. These GSCs essentially define what being a 'man' or 'woman' in that particular society entails.

Indeed, to the brain itself, the actual mapping of the body including the genitals does not differ between individuals with male or female primary sex characteristics. They are after all merely different configurations of the exact same organs, innervated by the exact same nerves. During sexual activity, brain activity is different between men and women, but this difference vanishes upon reaching orgasm [5], which considering especially the differences in the activation of the motor cortex in these studies could be argued to be mostly due to the different mechanical control requirements on the sides involved.


In a 2011 review study by Sedda [6] on the possible neurological causes behind Body Integrity Identity Disorder [7] (BIID), it is indicated that disruptions in the brain's somatosensory integration of the body's limbs may be due to some issue in the right parietal lobe, which would cause some parts of the body to be regarded as 'foreign' to the brain. Even though they can feel and see the affected limb, the parietal lobe issue causes the integration to fail.

Interestingly, body schema can also be affected with BIID in addition to body image. Here body schema refers to the dynamically updated awareness of where one's limbs and body are positioned in space at any given time. Body image is simply a description of the body. It is however argued that the terms of body image and body schema are too simplistic to fully cover the way that the brain integrates and maps the entirety of the body.

Fascinating about BIID is that the desire to have a limb amputated can change or even vanish. This might indicate a recovery of the SPL (superior parietal lobe) or other affected parts which originally caused the integration issue. All of this leads to the conclusion that perhaps the correct treatment for a disorder like BIID is not to perform the desired surgery, but to attempt to correct the underlying (neurological) cause without any surgery.


The mapping of the body to the brain is something which does not differ between individuals, as we all have the same basic body configuration. This is why something like phantom pains in people who have had limbs amputated is such a problem. Even with the physical limb gone, the mapping in the brain still exists and the parietal lobe among other parts of the brain keep trying to integrate it into one's perception.

This does however also mean that as long as the body part is still there, in whatever form or shape, the somatosensory experience is intact. In the case of individuals with more unique body configurations, such as true hermaphrodites (possessing both male and female genitals), the possession of both a vagina and a penis is of no concern, as there is no relevant innervation of the vagina, the penis is identical to the clitoris, and the presence of breasts is identical between men and women, despite absence of major fatty tissues and glands in the former.


As a hermaphroditic intersex person myself, this matches my own experiences quite well. My experience of 'gender' and the question of which sex I 'felt like' caused a great struggle for me, as I tried to make sense of these questions and concepts. In the end it became painfully obvious to me that none of those concepts and questions had any relevance to me, other than in a social context.

There are many things which I could change about my body's appearance within the context of sexuality, such as whether to have the penis reduced to a clitoris, undergo a mastectomy to have the (naturally developed) breasts removed, and of course have labia created in addition to having the (closed-off) vagina attached to the perineum (creating an entrance). Of these only the latter makes any sense to me, considering the negative consequences of having this closed-off vagina. Having labia is something completely optional to me, but since there's still skin literally hanging around there that serves no other purpose, one may as well.

The other two surgeries mentioned, they are about removing and reducing, involving invasive surgery, scarring and essentially damaging the body. They are surgeries which I would only consider in the context of something medically urgent, such as breast cancer. As my body did develop the way it did, however, I have no issues with accepting it the way it is. I feel no urge to conform to any kind of social standards, to be a 'typical woman' or 'typical man'. I got no need to compare my body in the context of 'male' or 'female'.


While reading through the studies that are now being published on this subject, and the strong evidence that the human brain does not in fact encode any kind of preference for a body configuration beyond essentially the expectation of at least having four limbs and five-fingered hands in addition to a few other bits hooked up, it makes one again understand why it's so easy for an intersex person to feel at home in an 'unusual' body, and for people born with extra parts or functionality (like the tetrachromats [8] among us).

There is also a limb attached to our body which we aren't normally aware of, even though it's still present: our tail. Though it ends in a little stump as it does for all ape species, if one were to make the appropriate genetic modifications, a human could have a fully developed tail, and it would feel as normal to have as one's arms.

All of this is to say that to try to cram the human body and its brain into one of two tiny boxes is to do a disservice to its amazing diversity, as well as the fascinating scientific reality that is only now unfolding for us.


Maya


[1] https://en.wikipedia.org/wiki/Sex_differences_in_crime
[2] https://www.pnas.org/content/112/50/15468
[3] https://mayaposch.blogspot.com/2019/12/gender-is-social-contract-not-part-of.html
[4] https://www.bccn-berlin.de/news/unisex-genital-maps-in-the-brain.html
[5] https://www.ncbi.nlm.nih.gov/pubmed/19219848
[6] Body Integrity Identity Disorder: From A Psychological to A Neurological Syndrome (DOI 10.1007/s11065-011-9186-6)
[7] https://en.wikipedia.org/wiki/Body_integrity_dysphoria
[8] https://en.wikipedia.org/wiki/Tetrachromacy