ask okay 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 Auto acoustic
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 dat
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 stria terminalis it's
where the amydala 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 neurot transmitter 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 large
sample size of transsexuals brains
postmortem 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 okay well maybe this is due to the
fact that when people change gender
transsexual ual 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 endocine
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
transexualism 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
transsexual 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 are of that sex but
they are 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 and employees now medical insurance
will cover transgender operations
however there's no evidence that the
Obscure endocrine Journal published at
AIA or something did that like the
afternoon before you know 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 okay how many of you know
about Phantom limb
syndrome okay 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 Fant P Phantom penol
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 have having their penises
removed 0% rate of penile Phantom
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 okay 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 sexual behavior
what in the environment is doing this or
that to the medial preoptic area or the
amydala or vasopress receptor levels or
any such thing what are the sensory
triggers for the neur