Wednesday, 9 November 2011

The Transsexual Brain

According to a new paper, the brains of male-to-female transexuals are no more "female" than those of men.

The authors write that "The present data do not support the notion that brains of male-to-female transexuals are feminized" and conclude "The present study does not support the dogma that male-to-female transexuals have atypical sex dimorphism in the brain".

That last sentence has gained quite a bit of coverage, including a quote on the Wikipedia page for "transgender".

But is it so simple?

Structural MRI scans were used to compare the size of various brain structures between three groups of volunteers: heterosexual men, heterosexual women and the transexuals (or "MtF"s as I will call them for short) who were diagnosed with gender dysphoria and were "genetically and phenotypically males".

There were 24 in each group, which makes it a decent sized study. None of the MtFs had started hormone treatment yet, so that wasn't a factor, and none of the women were on hormonal contraception.

The scans showed that the non-transsexual male and female brains differed in various ways. Male brains were larger overall but women had increases in the relative volumes of various areas. Male brains were also more asymmetrical.

The key finding was that on average, the MtF brains were not like the female ones. There were some significant differences from the male brains, but they weren't the same differences that distinguished the females from the males.

This is a fairly crude approach. It looks at the groups on average. It's a finding, but there's more you could with this data. It would be better perhaps to look at the male and female groups, and then try to work out which group each individual MtF is most similar to. You could do that using a Support Vector Machine such as was previously used to detect autism.

This would also have the advantage that it would integrate the results across different brain areas: maybe the important thing is not just the size of individual areas but the relative size of one area to another area.

My real problem though is with the language used to discuss the data. The authors say that the study doesn't support "atypical sex dimorphism in the brain" yet this wasn't a study of "the brain". It was a study of one specific aspect of the brain, namely the volume of different regions. There could be all kinds of chemical and microstructural differences that don't show up on these scans.

There are lots of people with severe epilepsy, for example, whose brains clearly differ in some major way from people without epilepsy, yet they look completely normal on MRI. Only using other methods, like EEG, reveals the difference. Because the difference is chemical, not structural.

I have no idea how, or if, the brains of MtF transsexuals are "feminized" but this study doesn't rule it out. Now I'm sure the authors know all this. And in fact they themselves recently published a paper showing atypical neural responses to smelling "oderous steroids" in transsexual people. But while neuroscientists will know what they meant, I worry that studies like this could be miscontrued by other people (like Wikipedia readers) as a result of overenthusiastic language in papers.

Link: Also blogged at BPS Research Digest. Savic I, & Arver S (2011). Sex dimorphism of the brain in male-to-female transsexuals. Cerebral cortex (New York, N.Y. : 1991), 21 (11), 2525-33 PMID: 21467211


petrossa said...

Jumping to conclusions is fast becoming a standard. First started with climatology it's now invading serious science.

I blame education. Since education is open for the masses the standards have dropped significantly to accommodate for mediocre students. Practically very few years standards get reevaluated according to the graduation rate.

Always downwards.

With sloppy papers by the 1000's as a result.

And wikipedia should carry a public health warning.

Bendert Katier said...

Interesting Article. We devoted our last journal of social sciences on the topic of gender roles and sexual identity. Thought you might enjoy it!

James Cantor said...

When in isolation, it is indeed possible to explain the Savic & Arver data by saying that that MtF brains are feminized, but in a way that does not show up on scans.

However, there are other data (i.e., Rametti et al., 2010) that when considered together, spell out a very different story: There are actually two independent TYPES of male-to-female transsexual, one of which does show a pattern of feminization, and one of which does not. This confirms the neuroanatomical prediction that was published by Blanchard (2008).

I have recently pointed this out in a Letter-to-the-Editor of the Archives of Sexual Behavior, which is available online as a .pdf, for those interested:

- James Cantor
twitter @jamescantorphd

practiCalfMRI said...

Is it standard procedure in this field to ignore the rest of the body? Surely there might be many, many measurements one might make (hand span, height, weight, hat size, etc.) that should be measured to ensure no systematic difference in brain regions and so on? Isn't this yet another example of correlation science fishing for causation?

NS, I like your idea of using an SVM or some other way to try to characterize "maleness" or "femaleness." I'd also want to see how "pretty" males or "masculine" female controls ranked, too. There are so many potential confounds here it boggles my mind.

Incomplete experiment if you ask me. I would need to see a lot more data before interpreting their "conclusions" at all.

James V. Kohl said...

I am commenting only on the abstract since I have not yet read the paper in its entirety. Excerpt: "...male groups had smaller hippocampal volumes than HeW." A clear connection between pheromones, luteinizing hormone (which also is involved in gray matter/white matter ratios)and hippocampal neurogenesis has been detailed. Given the role of the hippocampus in learning and memory during the development of sexual preferences, this might link pheromones to sexual orientation as did other works by Savic and her group.

Chris Brand said...

I'm curious as to why the study compared gynephilic men and MtF transexuals with androphilic women; it would have made more sense, to me at least, if the comparison had been made to gynephilic women. I haven't read the full article yet, so this might well be explained within.

skm said...

Thanks for posting this. I was dreading the possible outcomes of conversations where people would tell me that trans people don't exist.

Charlie said...

Thanks for the interesting article.

FYI, there's a term for people who are not transgender. Cisgender refers to people who experience and present their gender in a way that’s aligned with the sex of their body, as compared to transgender and transsexual people.

Collaterly said...

Hi! I'm a researcher who just finished a little over a year in a group using magnetic resonance spectroscopy and imaging to study brain and prostate cancer. I'm also transitioning to female.

I actually hadn't heard of the study that this blog post is about, and it's not hard to see why. The study is... well, I'm a little confused as to who would fund it, because it's terribly designed. Neuroskeptic is right to say that there could be finer structural differences in trans brains, but is actually being a little too cautious - we have detected these differences! More sophisticated MR techniques, such as DTI, have detected very interesting differences in white matter, neuron count, etc. that do suggest that trans peoples' brains have a number of subtle similarities to the brains of people born in their preferred gender.

That brings us back to this study. Why bother? Seriously, I don't want to be a spectral chauvinist, but why bother doing a volumetric study at all? It might have been excusable ten years ago, before we had better techniques, but when those techniques exist, and have been used to address this exact question, it's just stupid. Never mind that it is well-established that brain volume is hormonally-mediated. We wouldn't expect to see differences in volume in pre-HRT trans women, for instance. Were the study authors unaware of this? If so, what business did they have investigating trans issues without even a foggy grasp of the field?

A few resources: basically diffusion tensor imaging (DTI) is one of the most sophisticated functional MRI techniques available and is particularly useful because it shows us axonal tracts - you may have seen some really glitzy 3D images of the brain that look as though they're made up of lots of white cords. DTI and other, similar ways of generating contrast - all MRI images come from bulk changes in the relaxation times and magnetic properties of different kinds of tissue - have identified a few interesting things. There's a summary of one such study here that includes needed discussion of the baggage surrounding much trans research (Blanchard and other idiots)

Although not originally an MR study (it may since have been confirmed by MR,) the most widely-known brain difference result in trans research (the 1997 BSTc study) is summarized here:

glitterary said...

Hey, I really enjoy this blog and really appreciate the critical look it gave this study. As Collaterly pointed out, it seems a really blunt tool was used to try to look at a far more complex issue which has already been considered through more appropriate means.

I'm not a scientist, and looking at the linked articles there's a lot of terminology that seems to be used as standard in research which coming from a non-scientific background sounds offensive. Terms like "Male to female" have given way to "Male assigned at birth", and (as Charlie pointed out) it would be good to refer to non-trans people specifically as being cisgender--otherwise just using "women" when what is meant is "cisgender women" is exclusionary. While I accept I'm unfamiliar with the convention, would it be possible to indicate more clearly that the scientific terminology used is different to what is politically appropriate?

Richard said...

I pretty much agree with everything Collaterly said (and pretty much nothing petrossa said...), except that DTI isn't functional ;)

petrossa said...

I have that effect on people. :)
Unfortunately never with well founded arguments

Reneta Scian said...

The brain is the most complex organ in nature, point simple. This study appears to have sound data, but the an Office Space grade of "Jumping to Conclusions". Their data doesn't discuss or differentiate anything relating to sexual orientation which is demonstrated to have differences. Furthermore, MRIs on multiple occasions have shown transsexual brains to be morphologically distinct from both male and female brains, sometimes in between.

The study also doesn't compensate for cranial volume in it's data, in a comparative manner, and it fails to calculate in the effects of current sexual hormones into the equation. The study sounds dismissive and one-sided, though the data tells a story of it's own. That is what happens in science when you go into experimental testing with bias as a premise to experimentation.

To me, their conclusion appears to be invalid. Cranial volume is correlated to testosterone exposure of the bone structures (especially in puberty), therefore in structural analysis, you have to compensate for it. For a study like this to be truly revealing it would have to correlate with multiple types of scans, and include pre- and post-op transsexuals, both with and without hormones, and transsexuals who transitioned at puberty.

As a further amplification to understand the effects of hormones and brain structures, include intersexed people of both male and female spectrums and multiple histories to give the steroidal effects on CAH patients, and the estrogenic effects of HRT on cAIS patients. This study's conclusion is anecdotal, though the data isn't necessarily invalidated, just incomplete. I am in general agreement with Collaterly, and I think the methods and conclusions are woefully inadequate considering current methods.

Generally speaking, the contradicting the body of evidence for brain differences in transsexuals, plus the study's own data indicates reason enough to believe the conclusion is false. The commentary about not supporting "dogma" indicates to me a very biased opinion on the matter. Gender differences in the brain with transsexuality is a reasonable conclusion given the body of evidence the study is trying to refute.

Dogma, indicates a belief that someone is refusing to believe otherwise on principle, asserting the larger body of evidence was biased (or conspiracy). I personally wouldn't mind a scientific explanation for the phenomenon, but that study isn't it. Sound scientific method isn't eroded by bad studies, so long as you view everything with skepticism and refuse to take people at their word alone.

Anonymous said...

My goodness James Cantor must be paranoid that someone might think gay people are not born gay.

The MRI suggests AGP transsexuals are not born that way due to the plasticity of the brain, how ever DR Cantor knows for a fact chemically castrating an autogynephilie at 25 does not stop the dysphoria at 39, he has seen it for himself.

Savic and Arver say repetitive thinking may be responsible but when you take the agp away via castration from 25 to 39 and you still end up dysphoric like me at 39 its unlikely the change in the area of body perception is due to repetitive thinking.

As well, if the part of the mind responsible for body image and meditation is changed due to the mind being plastic then I would aslo expect the part of the mind that deals with shame and humiliation and fear to also be different, but its not.

Lets not forget autogynephilies are the only ones who are proven to be different via IQ scores, autogynephilies are for some reason highly intelligent. That my friend Dr Cantor is the only tangible data anyone has that is non negotiable that points to anything that's innate convulsively.

Jenna McCarthy

Anonymous said...

Sometimes, people just respond to environmental stimuli and do what they do. Maybe a little boy was born rather small, was picked on & treated like a girl. Maybe that had a psychological impact and resulted in insecurity about it's sexuality and worth as a man. And maybe it identified more with the weaker sex. And maybe it resulted in him surgically altering his body to look like a female. I believe the answer here has always been mental.

Sometimes, it cannot be explained with neurology, biology or physiology. The brain is a powerful thing...and I strongly believe the chemistry and physiology of the brain can change with different stimuli. I do not believe some men are born gay or with a female brain. I think science is order to be politically correct.

Anonymous said...

Not to be an ass, but 'transsexual' is misspelled in your title. (Spelled correctly in the text itself, though.)

Just thought you should know. Feel free to delete this comment after reading. :)

Neuroskeptic said...

Oops. Thanks. Fixed!