Monday, 6 June 2005

Brain Structure

In the course of doing research on hormonal changes to the body, I've come across a lot of data about a relatively minor change, but one with the most profound societal impacts. This post is about the bed nucleus of the stria terminalis (BSTc), a collection of cells in the hypothalamus. And about Identity and Society.

From GenderPsychology.Org: :
For most laymen the idea that experience can alter the structure of the brain may seem unlikely, but for over 30 years neuroscientists have provided demonstrations that this idea is quite correct. At Berkeley, David Krech, Mark Rosensweig and colleagues found that when rats were raised in enriched environments (with toys and other rats) rather than caged alone, the animals showed many reliable changes in brain structure. Shortly after, David Hubel and Torsten Wiesel of Harvard demonstrated that depriving kittens of visual stimulation to an eye would alter connections between the eye and the brain. Such demonstrations of experience altering brain structure have been extended to monkeys and, in recent years, to humans. For example, a human who had lost his hand as an adult showed clear evidence that the side of the brain controlling that hand was reorganized less than a year after the accident (Yang, T.T., Gallen, 0., Schwartz, B., Bloom, F. E., Ramachandran, V.S., & Cobb, S. Sensory maps in the human brain. Nature, 386, 592-593, 1994 [letter]). As noninvasive imaging techniques are perfected we can expect to see further demonstrations that experience can alter the adult human brain. Why am I so confident that there will be more such demonstrations? I'm well aware of how much humans can learn, how much they can alter their behavior, and how frequently they do so. All of this behavioral plasticity requires that something in the brain remain plastic, too.
All well and good, and utterly non-controversial. It then continues:
But there is another important feature of the recent work with transsexuals that we can all ponder. Whether these men were born with a small BSTc which caused them to become transsexuals, or whether these men became transsexuals which then caused them to have a small BSTc, the fact remains that their brains are physically different. And that difference is not trivial, because any difference we can detect with our primitive understanding of neuroanatomy is, by definition, not trivial. Thus we might regard transsexuality as a deep, abiding conviction. Presumably these adults could no more set aside their feelings about which sex they are than you or I could. So perhaps the report of Zhou et al. will make it easier for our society to accept and tolerate transsexuality.
I wouldn't bet on it. When people's long-cherished ideas of religion or morality are concerned, any inconvenient reality that challenges these beliefs is likely to be ignored. And in this case, the Jury is still out, anyway. From Anne Lawrence :
A recent paper by Chung et al. (2002) has demonstrated a most unexpected finding: In humans, unlike the rat and perhaps other species, BSTc volume does not become sexually dimorphic until well into adulthood. However, most MtF transsexuals report that they experienced gender dysphoria beginning in childhood, often from the time of their earliest memories. It is hard to imagine how BSTc volume could be a marker for gender identity if BSTc volume has not yet become sexually dimorphic at a time when gender identity has already been firmly established.
Oh yes, I'm having a brain MRI scan tomorrow, concentrating on the Pituitary gland.

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