In BIID, or apotemnophilia, individuals express a strong desire to have a healthy limb amputated at a very specific location. People with this condition usually describe the affected limb as being "intrusive" or "over-present", and report that they have had the desire to remove since early childhood, but do not understand why. This desire can be so strong that sufferers sometimes resort to damaging the affecting limb irreparably, thus forcing doctors to amputate it. The vast majority of BIID sufferers have no other psychological disturbances, and almost always say that they feel much happier when the limb is eventually amputated.I hypothesise that the difference between non-op and pre- or post-op transsexuals is caused by different degrees of masculinisation or feminisation of the superior parietal lobule.
A growing body of literature suggests that body awareness disorders such as BIID occur as a result of abnormal activity in the right parietal lobe, which is known to be essential for constructing a mental representation of the body. Specifically, this body image is constructed in the superior parietal lobule (SPL), which performs a function referred to as multisensory integration, whereby different types of sensory information entering the brain are brought together. Thus, information from the visual parts of the brain and the primary somatosensory cortex, which processes tactile sensations and proprioceptive information relating to the position of the body within space, is sent to the superior parietal lobule. There, it is combined with information from the motor cortex, which controls movement, and all is processed further to generate an internal model of the body. If these processes are perturbed, the body image is compromised.
In BIID, the situation is apparently reversed: the body image is missing a representation of the affected limb. But the body image distortion seen in BIID is almost certainly congenital. Children born with missing arms or legs sometimes experience phantom limb syndrome, suggesting that there is a representation of the limb in the brain, even though it has never existed. The body image is, therefore, probably "hard wired" during development. The experience of BIID sufferers is consistent with this, as they typically report that they have had the desire to have a limb amputated since early on in their lives. It seems the brains of apotemnophiles fail to generate a representation of the affected limb, because of some aberrant developmental mechanism. The limb has never been a component of the body image, so the afflicted person grows up believing that it feels "wrong", but cannot explain why.
The trouble is - I have no idea how to test this hypothesis. It fits with everything that we know, but that doesn't mean it's true.
All I can say is that when I was 4 years old, long before I had any concept of the differences between girls and boys, that what was "down there" felt... supernumary. Incorrect. Shouldn't be there. Furthermore, after genital reconstruction in 2006, things felt right. Not completely, there still seems something that should be there, in my abdomen, that isn't. But far, far closer to "natural" than before. Even things like urination are effortless, my instincts take over, whereas before I had to concentrate on what I was doing. I had to think, it was neither instinctive nor natural to have somewhat masculine anatomy, even if it didn't resemble the usual kind thereof.
That matches rather closely the description of BIID: but is normal for a woman, just as having a body image that involves external genitalia (and does not involve womb or cervix) is normal for a man.
I hope that one day, we'll be able to point to the areas of the brain that define gender identity more exactly, rather than "in the lymbic nucleus". That we will be able to do the same for sexual orientation, which is probably a very complex phenomenon, certainly involving sense of smell amongst other things, and be more exact than saying "it's in the hypothalamus and elsewhere". That we can do the same for male-vs-female toy preference, which has a strong correlation with sexual orientation amongst "effeminate" gay men and "butch" lesbian women; and finally, the body map in the superior parietal lobule. The latter appears to be more plastic than the others, but "more" here means "not very much".
Research on the latter might find palliative treatments for men who have been castrated, and women who have had vulvectomies, both of whom suffer the same kind of severe distress found in transsexuals. Distress that goes well beyond the problems caused by sexual incompetence. Reconstruction in conjunction with such treatment is the ideal course, but that may not be possible. The brain might need de-programming afterwards to remove the effects of the palliative treatment once reconstruction has been performed, or the patient gets BIID again.
More work needed. And as always, remembering that we're not dealing with machines here, but people, with feelings, emotions, human rights. I know that some researchers, at least, forget that. Maybe it's necessary not to get too involved in order to help people, but in some cases I think it's just pure lack of empathy towards those who are too different from themselves.