Ramachandran V S, McGeoch Paul D
Center for Brain and Cognition, UCSD, La Jolla, CA 92093, USA.
Med Hypotheses. 2007;69(5):1001-3. doi: 10.1016/j.mehy.2007.02.024. Epub 2007 Apr 8.
Transsexuals are individuals who identify as a member of the gender opposite to that which they are born. Many transsexuals report that they have always had a feeling of a mismatch between their inner gender-based "body image" and that of their body's actual physical form. Often transsexuals undergo gender reassignment surgery to convert their bodies to the sex they feel they should have been born. The vivid sensation of still having a limb although it has been amputated, a phantom limb, was first described by Weir Mitchell over a century ago. The same phenomenon is also occurs after amputation of the penis or a breast. Around 60% of men who have had to have their penis amputated for cancer will experience a phantom penis. It has recently been shown that a significant factor in these phantom sensations is "cross-activation" between the de-afferented cortex and surrounding areas. Despite this it also known that much of our body image is innately "hard-wired" into our brains; congenitally limbless patients can still experience phantom sensations. We hypothesise that, perhaps due to a dissociation during embryological development, the brains of transsexuals are "hard-wired" in manner, which is opposite to that of their biological sex. We go on to predict that male-to-female transsexuals will be much less likely to experience a phantom penis than a "normal" man who has had his penis amputated for another reason. The same will be true of female-to-male transsexuals who have had breast removal surgery. We also predict that some female-to-male transsexuals will have a phantom penis even although there is not one physically there. We believe that this is an easily testable hypothesis, which, if correct, would offer insights into both the basis of transsexuality and provide farther evidence that we have a gender specific body image, with a strong innate component that is "hard-wired" into our brains. This would furnish us with a better understanding the mechanism by which nature and nurture interact to link the brain-based internal body image with external sexual morphology. We would emphasise here that transsexuality should not be regarded as "abnormal" but instead as part of the spectrum of human behaviour.
易性症患者是指那些认定自己属于与出生时相反性别的人。许多易性症患者表示，他们内心基于性别的“身体形象”与身体的实际形态之间始终存在不匹配的感觉。易性症患者常常会接受性别重置手术，以使自己的身体转变为他们认为自己本应出生时的性别。尽管肢体已被截肢，但仍感觉它还存在，即幻肢现象，这一现象早在一个多世纪前就由韦尔·米切尔首次描述。阴茎或乳房被切除后也会出现同样的现象。因癌症而不得不切除阴茎的男性中，约60%会体验到幻阴茎。最近研究表明，这些幻感觉的一个重要因素是去传入皮层与周围区域之间的“交叉激活”。尽管如此，我们也知道，我们的许多身体形象在很大程度上是天生“硬连接”到大脑中的；先天性无肢体的患者仍然会体验到幻感觉。我们推测，也许由于胚胎发育过程中的分离，易性症患者的大脑以一种与其生理性别相反的方式“硬连接”。我们进而预测，男变女的易性症患者比因其他原因切除阴茎的“正常”男性体验到幻阴茎的可能性要小得多。接受乳房切除手术的女变男易性症患者也是如此。我们还预测，一些女变男易性症患者即使身体上没有阴茎也会体验到幻阴茎。我们认为这是一个易于验证的假设，如果正确，将有助于深入了解易性症的基础，并进一步证明我们有一个性别特异性的身体形象，其具有强烈的先天成分并“硬连接”到我们的大脑中。这将使我们更好地理解自然与养育相互作用，将基于大脑的内部身体形象与外部性形态联系起来的机制。在此我们要强调，易性症不应被视为“异常”，而应被视为人类行为谱系的一部分。
