Ask, OK, well, what about the neurobiology of sexual orientation in women? Vastly smaller literature. Far, far less studied. What has been showed so far are only two endpoints. One is the same deal with the fourth to second finger ratio.
On the average, gay women have the ratio more typical of straight men than straight women. The other thing that's been shown is the same autoacoustic reflex thingy going on there. Final realm of neurobiology.
rather than issues of gay versus straight, what is the neurobiology of transsexuality? And that used to be considered to be purely a domain of psychopathology. If being gay used to be a certifiable psychiatric disorder up until the early 1970s, the American Psychiatric Association, in their textbook, the Diagnostic Statistical Manual, you could be psychiatrically certified as ill, a psychiatric disorder.
was being homosexual or lesbian. And then in what had to have been one of the more all-time blowout committee meetings ever, they decided that no, actually it's not a psychiatric disorder. And overnight, about 40 million Americans were cured of a psychiatric disease. The notion of transsexuality as a psychiatric disorder has had much, much longer shelf life. What's the neurobiology of that?
To date, there have been a handful of studies And they show essentially the same thing. Really, really interesting. Another region of the brain that shows a sex difference in its average size. Don't even worry about the name of this. It's called the bed nucleus of the striae terminalis.
It's where the amygdala begins to send its projection into the hypothalamus. Another one to those gender differences. There's one type of neuron in there with a certain type of neurotransmitter where very, very reliably, It is about twice the size in males than in females, sufficiently so that even in human brains, you could pretty confidently determine the sex of somebody by seeing the number of these neurons.
You'll see I'm not even saying the name of the neurotransmitter. It's irrelevant. It's just another one of those differences, a dimorphism in a region of the brain, a really, really reliable one. And this was a study done by some superb neuroanatomists looking at transsexuals. And what they showed was very interesting, which was very, very reliably and a very powerful effect.
What you would see in their large sample size of transsexuals'brains post-mortem was people would have this part of the brain, the size, not of their sex that they were born with, but rather of the sex they insisted they always actually were. Wow. Immediate questions one must ask. OK, well maybe this is due to the fact that when people change gender, transsexual procedures, there's a whole lot of hormones involved. And maybe that's doing something to this part of the brain.
Critical control that they had was this was looking both at transsexuals who had made gender changes and those who went to their deathbed saying, this is not the sex that I am. I got the wrong body. but never made the change. It wasn't a function of having actually gone through the transition and the endocrine manipulations with it.
Another control they had, which was looking at men who would get a certain type of testicular cancer where they would have to be treated with certain feminizing hormones. In other words, very similar to some of the endocrine treatments of male to female transgendered individuals. And Postmortem, you didn't see the changes there.
It has nothing to do with the hormones. It had to do with the person insisting from day one that they got the wrong body. And this was a landmark study, fabulously well done and controlled and replicated once since then, showing that what transsexualism used to be thought of is that people who think that they're a different gender than they actually are.
What this study suggests is what transsexualism is about is People who got the wrong gendered body. And these are people who are chromosomally of one sex. In terms of their gonads, they're of that sex.
In terms of their hormones, they're of that sex. In terms of their genitalia and their secondary sexual characteristics, they're of that sex. But they're insisting, that's not who I really am. This part of the brain agrees with them. Also very interestingly, that study was done by the same Dutch scientists who did this one.
Again, this is very complex terrain in terms of what these things wind up implicating. Interestingly, that study was published right around the time that the city of San Francisco did something very cool, which was for city employees. Now, medical insurance will cover transgender operations. However, there's no evidence that the obscure endocrine journal published at a Latvia or something did that like the afternoon before.
The San Francisco commissioners had their meeting on that one. But nonetheless, this is a subject with all sorts of realms of implications. One additional study about transsexualism.
OK, how many of you know about phantom limb syndrome? OK. You are a guy with a penis.
And you get a certain type of penile cancer. And what's often done is your penis is excised. It is cut off. And about 60% of men who have had to have their penises removed because of cancer there wind up getting phantom penile sensations, which I don't want to know about.
What you see, though, is when you take transgendered individuals who go from male to female, in other words, as part of it, having their penises removed, 0% rate of penile phantoms. sensation, suggestion being that there is something much more normal in that case than when a penis is being removed for cancer. A whole new area of research, very novel, very challenging.
OK, so this has given us a sense now of this bucket. And we are now ready to move on to what in the environment releases some of these fixed action patterns of sexual behavior. What in the environment is doing this or that to the medial preoptic area, or the amygdala, or vasopressin receptor levels, or any such thing, what are the sensory triggers for the neurobrachial