Thursday, May 7, 2009

Gay and Lesbian Brains

Every aspect of your personality, every emotion, every idea, every gut feeling comes from a circuit in your brain. The ways that neurons connect to one another influence every aspect of who you are (and who you think you are). The brain is a massively complex web of circuits that activate and inhibit one another in response to external and internal stimuli. We understand a LOT about how the brain works, and we have still only scratched the surface. One thing is clear, though; variations in the physical structures of the brain are indicators of LARGE psychological differences. Many studies, especially recent ones, have found very interesting structural differences between gay men, lesbians, and straight men and women. These differences have direct psychological relevance – especially with respect to behavior and cognitive abilities.

Using fMRI and PET imaging, an article published in 2006 examined the activation of the brain in response to photographs of male and female faces. They found that male (but not female) faces excited the thalamus and medial prefrontal cortex of gay men and straight women, and female (but not male) faces excited the same area in lesbians and straight men [1]. The thalamus synchronizes and regulates responses to sensory information coming into the brain. All sensory inputs (touch, vision, and hearing) except smell go through the thalamus BEFORE they go to any part of the brain involved in perception or memory. Activation of the thalamus is NOT under conscious control. The prefrontal cortex controls planning and judgment of consequences. It is the part of the brain that listens to the thalamus and decides what is an acceptable behavior or not. [Interesting Tidbit: Severing the prefrontal cortex from the rest of the brain is called a frontal lobotomy. Alcohol also temporarily weakens this connection. It effectively eliminates your ability to “check yourself before you wreck yourself.”] This is the foundation of attraction. For some unknown reason, the brain decides on its own whether or not to pay particular attention to a male or female face based on some inherent preference, suggesting that sexual orientation is hard wired (literally) into the basic response system of the human brain. This was not examined in Bisexuals.

I don’t have the ability to explain the relevance of this next part yet (I’m just an undergrad!), but here is a short list of structural differences in the brain that have been found to be dimorphic with respect to sexual orientation:
[for simplicity, I’m going to refer to gay men and straight women as “Male Oriented Individuals” (MOIs) and lesbians and straight men as “Female Oriented Individuals” (FOIs)]

FOIs have larger right hemispheres than left, whereas MOIs have symmetrical hemispheres [2]. This is possibly linked to the fact that FOIs also have a smaller anterior commissure (not verified in lesbians – only MOIs versus straight men) which connects the right and left temporal lobes [3]. FOIs also differ from MOIs in their amygdalae (the part that controls emotional fear responses and houses fear memories). Certain stimuli have fear reflex loops in the brain which are “built in” during development such as the instinctual fear of hissing noises. FOIs have more connections from the right amygdala mainly to the caudate, putamen (both of which are part of the basal ganglia => motion), and the prefrontal cortex. MOIs have more connections from the left amygdala mainly to the right amygdala and the anterior cingulate gyrus (which is massively involved in memory formation and retrieval) [2].

A few studies have not been replicated in women, but still show dimorphism with respect to sexual orientation. The suprachiasmatic nucleus (the brain’s “clock”) is twice as large in gay men [4]. I have no idea what this could mean, but it is interesting because further research produced this same enlargement in rats by causing an atypical interaction between sex hormones and the developing prenatal brain. They used aromatase inhibitors which prevented testosterone from being converted to estrogens. It needs to be converted to have a large effect because there are estrogen receptors in more parts of the brain than testosterone receptors.

The next bit of cool research deals with the hypothalamus, a small part of the brain located just above the roof of your mouth. Don’t let its size fool you. Just a few of the functions that are controlled at least in part by the hypothalamus are the sympathetic and parasympathetic nervous systems, the secretion of hormones from the pituitary gland, circadian rhythms, and sexual and reproductive behavior. Almost all known neurotransmitters have an effect on some part of the hypothalamus.

Compared to straight men, the hypothalamus of gay men is less responsive to a selective serotonin reuptake inhibitor (SSRI) called fluoxetine [5]. This suggests some kind of difference in the serotonergic system, which regulates LOTS of things including mood and sexual behavior, with respect to sexual orientation in males.

In 2005 and 2006, two articles were published that studied the effect of male and female secreted pheromones on the hypothalamus. They found that male pheromones stimulated the anterior hypothalamus of MOIs, but not FOIs [6]. Similarly, female pheromones activated these same areas in FOIs, but not MOIs [7]. It has been demonstrated in numerous different species, including humans, that pheromones play a part in the regulation of sexual and reproductive behavior. This is just another example of a system that is dimorphic with respect to sexual orientation and is also not under conscious control. Many of the top researchers in the field believe that these differences could only have formed before birth (probably due to the influence of sex hormones), thus they were not caused by any behaviors. This means that there is more and more data piling up that directly contradicts any argument of “choice.”

Unfortunately, since we don’t know everything about the brain, we can’t actually make that statement. That’s the limitation of science: there’s always a pesky “what if.”

So now you know that there is evidence for sexual-orientation-dimorphic variations in brain structures that are integral to behavior. The influence of these structures seems to cause behavioral differences, and it’s possible that others may be able to consciously perceive those behavioral differences. In January of this year, a study was published that examined whether gay men and lesbians who were instructed to “act straight” would still be identified as queer by straight men and women. The participants in the study were all videotaped and asked to behave normally, sex-typically, and sex-atypically while talking about the weather. Then they were recorded while performing a mock interview for their dream job. They were told that their interviewer was either queer-friendly or not queer-friendly, and for the latter condition queer participants were instructed to “act straight.” Heterosexual men and women were asked to identify the participant as gay, lesbian, or straight after watching each scenario. In both scenarios where the lesbians and gay men were either acting sex-typically or straight, they were still identified as significantly more likely to be queer than heterosexual men and women acting normally [8]. These findings suggest that it may be very difficult to conceal your sexual orientation, and it would then be unfair to ask someone to do so – especially if they are stressed or under a high cognitive load already (as is the case with Don’t Ask/Don’t Tell). It also emphasizes the need for legislation that protects children from bullying in schools because of sexual orientation, since queer youth could be easily identified and may not even have the capacity to “act straight” in the first place.

I’m not suggesting that this is a biological basis for gaydar, but it is a very interesting outcome. There are many different reasons why the viewers could pick out the queer participants. Maybe it was because they used more stereotypical phrases or body gestures without being consciously aware of it. This could be due to the influence of gender roles, and one might even find the results completely different if the videotaped participants were actively closeted gay and lesbian adults or youth who had a lot of recent practice “acting straight”. The problem here is that we don’t know because no one has really studied this in depth. Science is working on it, though. In time, we will have more answers.

1 comment:

  1. [1] Kranz, F., & Ishai, A., (2006). Face perception is modulated by sexual perception. Current Biology, 16, 63-68.
    [2] Savic, I., & Lindstrom, P. (2008). PET and MRI show differences in cerebral asymmetry and functional connectivity between homo- and heterosexual subjects.
    Proceedings of the National Academy of Sciences USA, 105, 9403-9408.
    [3] Allen, L., & Gorski, R. (1992). Sexual orientation and the size of the anterior commissure in the human brain. Proceedings of the National Academy of Sciences USA, 89, 7199-7202.
    [4] Swaab, D., & Hofman, M. (1990). An enlarged suprachiasmatic nucleus in homosexual men. Brain Research, 537, 141-148.
    [5] Kinnunen, L., Moltz, H., Mets, J., & Cooper, M. (2004). Differential brain activation in exclusively homosexual and heterosexual men produced by the selective serotonin reuptake inhibitor, fluoxetine. Brain Research, 1024, 251-254
    [6] Savik, I., Berglund., H., & Lindstrom, P. (2005). Brain response to putative pheromones in homosexual men. Proceedings of the National Academy of Sciences USA, 102, 7356-7361.
    [7] Berglund, H., Lindstrom, P., & Savik, I. (2006). Brain response to putative pheromones in lesbian women. Proceedings of the National Academy of Sciences USA, 103, 8269-8274
    [8] Sylva, D., Riegner, G., Linsenmeier, J., & Bailey, J. (2009). Concealment of sexual orientation. Archives of Sexual Behavior, published online January 24.