Monday, 6 April 2009
Another Piece of the Puzzle
And a really useful and interesting one this time.
In the past, I've talked about how transsexuality being a "male brain
in a female body", or the reverse, while true, is only an
approximation. That it would be more accurate to say "masculinised
brain in a feminised body", or the reverse.
That's partly because so many "transsexual" people have been shown to
be not only neurologically Intersexed, but somatically intersexed in
other ways too. But it's also partly because not all of the neurology
need be affected to cause transsexuality, only parts. We're still
finding out what parts, and to what degree they are cross-gendered.
Professor Italiano (to whom many thanks) has just drawn my attention
to a new study. One that gives us more specific information than we've
had in the past.
Regional gray matter variation in male-to-female transsexualism
Gaser C, Toga AW, Narr KL, Hamilton LS, Vilain E. in Neuroimage. 2009
Mar 30.
We analyzed MRI data of 24 male-to-female (MTF) transsexuals not
yet treated with cross-sex hormones in order to determine whether gray
matter volumes in MTF transsexuals more closely resemble people who
share their biological sex (30 control men), or people who share their
gender identity (30 control women). Results revealed that regional
gray matter variation in MTF transsexuals is more similar to the
pattern found in men than in women. However, MTF transsexuals show a
significantly larger volume of regional gray matter in the right
putamen compared to men. These findings provide new evidence that
transsexualism is associated with distinct cerebral pattern, which
supports the assumption that brain anatomy plays a role in gender
identity.
So in some ways, the feminised brains of TS women more closely
resemble a typical male pattern, but in one specific way, they
resemble a typically female pattern.
The mean age (SD) of the MTF transsexuals was 46.73 (13.18) years
with an age range between 23 and 72 years. Male and female control
subjects were closely age-matched (males 46.57±12.45, 23–69 years;
females 46.77±12.88, 23–73 years). Transsexual subjects were 76%
dextral, control males were 93% dextral, and control females were 90%
dextral, where handedness was determined based on self-reports of hand
preference for selected activities. For study inclusion, transsexual
subjects needed to self-identify as a MTF transsexual, report no
history of hormonal treatment, and declare the intention ofundergoing
estrogen replacement therapy. MTF transsexuals were evaluated to be
free of psychosis according to a standardized diagnostic interview
(Robins et al., 1989) and confirmed to be genetic males as defined by
the presence of the SRY gene in their genome (Jordan et al.,2002). All
control subjects had to pass a physical and neurological screening
examination performed by a neurologist.
A couple of remarks here:
1. Mean age between 45 and 50, so most of the TS women would be
"late transitioners".
2. 3/4 were right handed, compared to 9/10 in the control groups.
Transsexuality is associated with ambidexterity, and to a lesser
extent, left-handedness. That gives us a clue that laterisation of the
brain is often affected.
3. Presence or absence of the SrY gene is not definitive as an
indication that the TS women weren't Intersexed - either (46xx/46xy)
mosaicism or Kleinfelter syndrome (47xxy) would be evaluated as
"male".
Back to the paper...
...we detected significant differences between MTF transsexuals,
males, and females in a large number of regions across the brain. More
specifically, within the frontal lobe, we observed gray matter volume
differences bilaterally in the superior frontal gyrus, close to
midline and also at the frontal pole, as well as within the right
orbital gyrus. Furthermore, we noticed pronounced gray matter volume
differences bilaterally across the occipital and posterior temporal
lobes, as well as in the parietal lobe, near the intraparietal sulcus,
and closer to midline (left). Additional group effects on regional
gray matter volume were detected subcallosally in both hemispheres at
the brain midline. These regions constitute part of the basal ganglia
(i.e., the caudate nucleus and putamen) and limbic system (i.e., the
subcallosal gyrus, mammillary body, amygdala, thalamus and
hypothalamus). Moreover, we identified two clusters indicating group
differences on the basal surface of the right temporal lobe and left
frontal lobe.
Ok, so the lymbic system is highly sexually dimorphic, something we
already knew. What's interesting is the other parts of the brain,
where sexual dimorphism has been inferred by fMRI imaging of blood
flow, but relatively little work has been done on the physical
structure.
Gosh I love this! It's a detective story, where we're being given
clues. Moving right along... now comes the juicy bits.
Altogether, females had the largest gray matter volumes in all but
two significant clusters, which were located in the left and right
putamen. Here, MTF transsexuals had the largest gray matter volumes
More "typically feminine" than the usual factory model... or should we
say that most women are less "typically female" than TS women? Less
"strongly gendered" on average? You'd expect TS women to be more
"strongly gendered" than average, as many would otherwise be able to
cope with transsexuality without seeking treatment. But what about the
rest of the brain? Many TS women show more typically male abilities in
instinctive ballistics calculations for example.
For the remaining clusters, MTF transsexuals had the smallest gray
matter volumes, but their data spectrum largely overlapped with that
of males.
Fascinating! Not just more female than female in some areas, but
slightly more male than male in others! I wonder, is this
environmental? Would the same thing be shown in younger, "primary"
transwomen? Or could it be that the anomalous hormonal wash in the
womb bollixes things up in an even more complex manner than we
thought? We're in the realm of conjecture here, so we can't say
without a lot more study. One thing - there's a correlation between
Transexuality and what has been described as "ultra male syndrome" -
Asperger's. Might this "ultra-male" grey matter pattern be the cause?
And could a change to a female hormone regime cause changes to it? I'd
love to see this repeated not just for younger transitioners, but for
those on various HRT regimes, and FtoMs too of course. There's so much
we don't know, but now we may be able to find out!
Overall, our study provides evidence that MTF transsexuals possess
regional gray matter volumes mostly consistent with control males.
However, the putamen was found to be “feminized” in MTF transsexuals.
That is, the gray matter volume of this particular structure in the
MTF transsexual group was both larger than in males and within the
average range of females. Interestingly, in a positron emission
tomography (PET) study, it was demonstrated that the left putamen in a
sample of MTF transsexuals (n=12), who had no history of estrogen
treatment, activated differently to odorous steroids when compared to
control males (Berglund et al., 2008). Taken together, these findings
lend support to the hypothesis that specific neuroanatomical features
are associated with transsexual identity, where the particular role of
the putamen requires investigation in future studies.
All good science discusses the implications of the work, and what
pitfalls might arise in drawing definite conclusions from it. And this
work is good science.
Further research needs to resolve whether the observed distinct
features in the brains of transsexuals influence their gender identity
or possibly are a consequence of being transsexual.
Alternatively, other variables may be independently affecting both
the expression of a transsexual identity and the neuroanatomy in
transsexuals that led to the observed association between both. Some
possible candidates include genetic predisposition, psychosocial and
environmental influences, hormonal exposures, or most likely an
interplay between these variables. In support of the influence of
genetics and environment, multiple cases of variations in MTF
transsexuals (Hare et al., 2009; Henningsson et al., 2005).
Furthermore, both transsexualism occurring within families have been
reported (Green, 2000) as well as studies on heritability in twins
(Coolidge et al., 2002) and preliminary findings on specific genetic
SC variations in MTF transsexuals (Hare et al., 2009; Henningsson et
al., 2005). Furthermore, both genes and environmental demands have
been demonstrated to determine brain anatomy (e.g., regional gray
matter) (Draganski et al., 2004; Thompson et al., 2001). Finally,
hormones have been shown to affect brain development (Arnold and
Gorski, 1984), and neuroanatomical alterations in MTF transsexuals
(Kruijver et al., 2000; Zhou et al., 1995) have been detected in
cerebral structures shown to significantly change in response to
hormonal exposure (Del et al.,1987; Guillamon et al., 1988).
No-one said it would be easy. And there may be many distinct
etiologies leading to the same result. Perhaps sometimes the brain is
cross-gendered ab initio, and sometimes it changes.
From my own experience, I can give the following data points. n=1 I
know, but what can you do?
1. My sense of smell changed, and early, within weeks
2. I became able to read body language over a month. Many of my
Asperger's symptoms disappeared.
3. My co-workers remarked about how, well, less dominant I became
at meetings. Shy, even. Maidenly modesty, if you like.
4. Other aspects of my personality changed too, but over a longer period.
I recorded this at the time, before any of these study results came
out. And published them on my blog... That would seem to indicate that
hormones post-birth may activate an atypical predisposition. Certainly
my brain got re-wired, something I found most disturbing! Now I might
have a clue as to what changed neurologically, and to what extent.
And yet, despite all the changes, in many ways I'm still that 10 year
old girl who picked the name Zoe, back in 1968. Just as thrilled at
solving puzzles and finding things new.
at 4/06/2009 03:32:00 PM
Labels: Brains, Science, Transition
http://aebrain.blogspot.com/2009/04/another-piece-of-puzzle.html
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