Sexual orientation and its basis in brain structure and function

[Ferrum Phos]

Sexual orientation and its basis in brain structure and function

Current evidence indicates that sexual differentiation of the human brain occurs during fetal and neonatal development and programs our gender identity—our feeling of being male or female and our sexual orientation as hetero-, homo-, or bisexual. This sexual differentiation process is accompanied by many structural and functional brain differences among these groups (1). In previous studies (2, 3), the Savic laboratory detected a sex-differentiated activation of the anterior hypothalamus in heterosexual men (HeM) and heterosexual women (HeW) and a sex-atypical, almost reversed, pattern of activation in homosexual men (HoM) and homosexual women (HoW).

In a recent issue of PNAS, Savic and Lindström (4) reported that hemispheric ratios, as well as patterns of amygdala connectivity, were sex-atypical in homosexual individuals, with HoM exhibiting more female patterns than HeM and HoW showing more male-like features than HeW. Whether the observed sex-atypical characteristics are the result of processes that occur during the fetal or neonatal periods, as is the case with gender identity and sexual orientation, is an open question. The excellent imaging research of Ivanka Savic's group in past years has provided strong evidence for structural and functional brain differences related to gender and sexual orientation.

In 1990, we described the first brain difference related to sexual orientation in the suprachiasmatic nucleus (SCN)—the brain's “clock”—which in HoM is twice the size that it is in HeM (6). In 1991, LeVay (8) reported that HoM, like HeW, have a smaller area in the frontal part of the hypothalamus (the INAH-3) than do HeM. In 1992, Allen and Gorski (9) found that the anterior commissure (Fig. 1) of HoM is larger than that of HeM. This structure, which is larger in women than in men, connects the left and right temporal cortexes and is thus involved in sex differences related to cognitive abilities and language. This difference may be related to the sex-atypical hemispheric asymmetries in HoM and HoW as seen by Savic and Lindström (4). The hypothalamus of HoM, it turned out, was not as responsive to a classic antidepressant (fluoxetine) as that of HeM, which points to a difference in the activity of the serotonergic system. Subsequently, Savic et al. (2) studied the effect of scent—in particular, a pheromone derived from progesterone and excreted in perspiration in concentrations 10 times higher in men than in women. Although pheromones influence sexual behavior and stimulate activation in the hypothalamus of HeW and HoM in the same way, this pheromone did not elicit a response in the hypothalamus of HeM. Pheromones thus may play a part in our behavior related to sexual orientation.

A follow-up study (3) showed that HoW reacted in a sex-atypical, almost reciprocal, way to pheromones as compared with HeW, again indicating that some hypothalamic circuits function in relation to sexual orientation. Kranz and Ishai (11) expanded this observation to cortical areas. Functional MRI was used to measure activity changes in the brain when pictures of men and women were shown to subjects. Viewing a female face produced a strong reaction in the thalamus and medial prefrontal cortex of HeM and HoW, whereas in HoM and HeW these structures reacted more strongly to the face of a man.

Savic's previous studies raised the question of whether certain sexually dimorphic features in the brain that are unlikely to be directly involved in reproduction may differ between homosexual and heterosexual individuals. The article by Savic and Lindström (4) provides the answer. The authors measured hemispheric asymmetry with MRI volumetry and functional connectivity of the amygdala with PET scans of cerebral blood flow. In HeM and HoW, volumetric measurements showed a rightward cerebral asymmetry, whereas the volumes of the cerebral hemispheres were symmetrical in HoM and HeW. Moreover, homosexual subjects also showed sex-atypical amygdala connections. In HoM, as in HeW, the connections were more widespread from the left amygdala. In HoW and HeM, on the other hand, they were more widespread from the right amygdala. Furthermore, in HoM and HeW the connections were primarily displayed with the contralateral amygdala and the anterior cingulate; in HeM and HoW, they were displayed with the caudate, putamen, and prefrontal cortex. Savic and Lindström describe sex-atypical cerebral asymmetry and functional connections in homosexual subjects that cannot be primarily linked to reproduction and suggest a link between sexual orientation and neurobiological entities. Neurobiological research related to sexual orientation in humans is only just gathering momentum, but the evidence already shows that humans have a vast array of brain differences, not only in relation to gender, but also in relation to sexual orientation.

A Difference in Hypothalamic Structure between Heterosexual and Homosexual Men on JSTOR

Abstract
The anterior hypothalamus of the brain participates in the regulation of male-typical sexual behavior. The volumes of four cell groups in this region [interstitial nuclei of the anterior hypothalamus (INAH) 1, 2, 3, and 4] were measured in postmortem tissue from three subject groups: women, men who were presumed to be heterosexual, and homosexual men. No differences were found between the groups in the volumes of INAH 1, 2, or 4. As has been reported previously, INAH 3 was more than twice as large in the heterosexual men as in the women. It was also, however, more than twice as large in the heterosexual men as in the homosexual men. This finding indicates that INAH is dimorphic with sexual orientation, at least in men, and suggests that sexual orientation has a biological substrate.

 

[Pressure]

IN.

 

[Menelik II]

but this would imply conversion therapy wouldn't work

 

[Maschine_Man]

So homosexuality may be inborn....that's fine with me, now hopefully these religious fukks can let ppl live.




































Now if we can just get the other side to accept that there are only two biological sexes then we can all move on from this.

 

[Ferrum Phos]

but this would imply conversion therapy wouldn't work

It doesn't..

Also, I'm reading that success merely means making heterosexual feeling possible. This doesn't mean that the homosexual feelings are eliminated.

 

[Pressure]

Now if we can just get the other side to accept that there are only two biological sexes then we can all move on from this.

An extreme majority of people aren't making that argument.

But you have made a convincing argument to be Negged.

 

[AndroidHero]

Interesting study.

 

[Maschine_Man]

An extreme majority of people aren't making that argument.

But you have made a convincing argument to be Negged.

Hard to get negged by someone that's ignoring you......

 

[Joe Sixpack]

Hard to get negged by someone that's ignoring you......

It can happen. I put that idiot Gil Scott Heroin on ignore and that fakkit still has the capability of negging me

 

[Maschine_Man]

It can happen. I put that idiot Gil Scott Heroin on ignore and that fakkit still has the capability of negging me

nah, he had ME on ignore (apparently) and now is saying he wants to neg me.

Regardless, the negs don't mean shyt, and if that is a reason that he wants to neg me to feel better about it, then he can by all means do what he wants.

ppl that get that sensitive over these types of things online got their own issues to work out. I'll let them have that.
I'll wear that crown of thorns and take whatever is burdening him off of them.



As for this conversation, I couldn't care less if science discovers that homosexuality is biological or not, I personally don't care how anyone lives their own personal lives.
If this discovery proves it's biological that is great, if it doesn't, but leads to more research, that is great too. my only issue is when ppl want to use science as a tool or a weapon in a fight for one thing, but totally disregard it for other things.

his deflection of that point was telling though.