Tuesday 29 October 2013

Open Minded Health

Open Minded Health - Results of Transsexual Brain Studies (as at 2011)


The amount of research that has been completed on the differences between transsexual and cissexual brains is small, but suggestive. Some areas of the brain appear to be sexually dimorphic irrespective of genetics or hormones (e.g., BSTc), whereas others appear to be more dependent upon sex hormones (e.g., brain volume). From the results of these studies, one may infer that pre-transition transsexual women’s brains are feminine in the BSTc and INAH3, partially feminine in their white matter tracts, and masculine in total brain and hypothalamic volume. Data in transsexual men is rarer because these studies are conducted in the western world, where transsexual women outnumber transsexual men (Gooren, 2006). However, studies of transsexual men appear to imply that the reverse is true for them.
These studies have numerous limitations. First, they have yet to be replicated. Replication is needed to ensure reliability and generalizability of these results. Second, these studies (especially those involving deceased brains) have small numbers of subjects, especially for the transsexual subjects. Studies involving brains from the Netherlands Brain Bank typically had fewer than 10 transsexual brains to study, and the latter two (Kruijver et al, Chung et al) only had a single transsexual male brain. Although fewer numbers of subjects are generally more acceptable in biological research than in psychological research, it is still a potential source of error.
Potentially the most glaring limitation in these studies is their conflation of sexual orientation and gender identity. Berglund et al (2008), for example, only compared heterosexual cissexual women and men with gynephilic/homosexual transsexual women. While they could not include androphilic/heterosexual transsexual women in their study because of rarity, they failed to include homosexual cissexual men and women as comparison groups. This introduces a potentially confounding variable.
Despite these limitations, evidence so far is suggestive of a biological influence in transsexuality. More research is needed to confirm and expand these preliminary findings.
Some of these criticisms have been met - at least partially - since 2011. Others remain. As a summary of the state-of-the-art back then, I could only improve on it marginally.


Billie said...

I'm impressed you find time to read all this stuff! Thanks, Zoe.

Anonymous said...

The bigger problem is expected gender roles. One size does not fit all with culture and society setting standards for gender expression we have the huge problem of people not fitting into society.


Anonymous said...


Why can't tests be carried out on the size of brains, and the size of individual parts of the brain in cis and trans people while they are alive?

and ...

If the size of our brains and individual parts of our brains occur from birth ... congenital ... then that would qualify transsexuality as a type of intersex would it not?


Zoe Brain said...

Hi Nicole

To answer your questions - two things. It's not yet ready for "prime time", we're still gathering data. We need numbers and error-bounds, confidence-intervals. As there's significant overlap, we'd need multiple measurements of different areas. Exactly which areas, we'd need to determine. At the moment, study is concentrated on obvious cases, but to be useful, they'd have to deal with boundary ones too.

That's the first issue. The second issue is that after all of the MRIs and PET scans, the hundreds of thousands of dollars costs... we'd have a diagnostic protocol that may be no more reliable than the current ones, involving psych assessment, self-assessment, and observation. That's already at the 90%+ level, astoundingly reliable by medical standards.

There are a few tests that seem to be more reliable still, and quite cheap. Definitive. Unfortunately these involve slicing the brain up and examining it under a microscope, which has obvious disadvantages as a practical diagnostic technique!

Zoe Brain said...

As regards "Transsexuality as an Intersex condition" - see Prof Milton Diamond's presentation to the 2009 APA annual meeting.

Symposium Title: The Neurobiological Evidence for Transgenderism

I have Prof Ecker's presentation here, but not Milton Diamond's.

His was entitled Transsexuality as an Intersex Condition

Although there are good practical reasons for considering Transsexuality as a separate issue, yes, Transsexuality is a subset of Intersex. There are many other Intersex conditions too, all varying in legislative and medical needs, and to add TS to them would just confuse the issue further, according to IS activists who I have a great deal of respect for.

So I don't emphasise this aspect too much. Let the facts speak for themselves, and others draw the obvious conclusions.