A phantom limb is the feeling that amputees often have that the missing limb is still attached and giving sensations. More than 50% of amputees experience a phantom limb. Phantom breast sensations can likewise occur after mastectomy.Unfortunately, sensations from a phantom body part are usually painful and that pain is almost impossible to treat, even though the pain is very real, not imaginary.
There is a section of the cerebral cortex of the brain where nerve signals from major body parts go. In a typical drawing of this somatosensory cortex, the amount of cortex dedicated to a particular body part is represented by the relative size of a drawing of that body part. The face, lips, and tongue use a large part of the somatosensory cortex, and that corresponds to our experience that these parts of the body are well-innervated and particularly sensitive, compared, say, to the middle of the back.
There are two of these somatosensory cortexes, one on each side of the brain. The left somatosensory cortex represents the right side of the body, and vice-versa. Normally, if your right hand is stimulated, nerves would fire in the left somatosensory cortex, in the area corresponding to the right hand.The best explanation for phantom pain is that neurons fire in the relevant area of the somatosensory cortex, causing the sensation in the corresponding body part, whether or not that body part is actually present.
Why would neurons in the somatosensory cortex fire in the absence of the corresponding body part? There is some evidence that nearby areas “take over” the part of the cortex that had been used by the lost body part (Ramachandran, Rogers-Ramachandran & Stewart 1992). The brain acts as if it believed there is no reason to let perfectly good cortex go to waste just because a body part has been amputated. The result can be the experience of a phantom limb and its phantom pain.
In an interesting new study, Ramachandran and McGeoch (2008) surveyed a sample of transgender individuals (also called transsexuals), people who have chosen to change from one sex to the other through use of hormones and surgery. About one out of 2500 males underwent transsexual surgery in the U.S. in the last four decades (Conway, 2002). If you count those men who experience “intense gender dysphoria” (unhappiness with their anatomical gender and desire to be the other gender), but who have not undergone surgery, the frequency is one out of 500. So while uncommon, this is by no means a rare situation.
Ramachandran and MGeoch sampled both male to female (MtF) and female to male (FtM) transgender cases. They asked these individuals if they have ever experienced a phantom penis or phantom breasts. They discovered:
1. Among 29 FtM individuals 62% reported a vivid phantom penis, including phantom erections. Many said they had experienced these phantoms for years, well before the transgender program of hormone therapy. These are people who were born female, so finding such a large incidence of phantom penis sensations in people who had never in their lives had a penis, is remarkable to say the least.
For comparison, the authors interviewed a sample of ten college-aged females who were not transgendered, and none of them reported ever having anything like phantom penis sensations.
The implication is that for some reason the transgender females had the representation of a male’s body in their somatosensory cortex, giving them phantom penis sensations. Ordinary females have a female body represented in their cortex so they would not have phantom penis experiences.
2. Three of the 29 FtMs had postoperative phantom breast sensations. The breasts are typically removed as part of the transgender process. In the general population of women, 33% experience phantom breast sensations after mastectomy.
Why do the FtMs have such a low rate of phantom breast (only 10%), while in the general population it is 33%? The implication is that fewer transgender FtMs have breasts represented in their somatosensory cortex to begin with, so when the breasts are removed, there are no phantoms.
3. Among MtF transgender subjects, 30% experienced a phantom penis after penectomy. Based on published studies of penectomy, such as for malignancy, in the general population, 58% of men experience a phantom penis after the organ is removed.
Why would only 30% of men experience a phantom penis in the MtF group? Presumably, that group includes more men who did not have a penis represented in their somatosensory cortex in the first place, so when the organ was removed, they did not experience a phantom.
Taken together, these findings suggest that a person’s body concept and gender identity are strongly influenced by the neurological mapping of the somatosensory cortex. In the case of transgender individuals, it looks like the brain representation may have a stronger influence than even a lifetime of gender socialization and personal experience living in that body.
Regardless of the plain facts of their bodies and the advice of their social community, transgender individuals undergo enormous anxiety, trauma, risk and expense to get their body morphology lined up with their brain circuits.
This research seems to support the notion that when it comes to gender identity, anatomy is destiny – brain anatomy, not sexual morphology. And it seemingly refutes the idea that gender identity is merely a learned set of social attitudes and behaviors, as some philosophers have argued (e.g., Butler, 1990, 1993).
References:
Butler, J. (1990). Gender Trouble: Feminism and the Subversion of Identity. New York: Routledge.
Butler, J. (1993). Bodies that Matter: On the Discursive Limits of 'Sex'. New York: Routledge.
Conway. L. (2002). How Frequently Does Transsexualism Occur? Retrieved from http://ai.eecs.umich.edu/people/conway/TS/TSprevalence.html on March 5, 2008.
Ramachandran, V.S., & McGeoch, P. D. (2008). Phantom penises in transsexuals: evidence of an innate gender-specific body image in the brain. Journal of Consciousness Studies, 15 (1), 5-16.
Ramachandran, V. S.; D. C. Rogers-Ramachandran & M. Stewart (1992), "Perceptual correlates of massive cortical reorganization.", Science (no. 258(5085)): 1159-1160
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