This post summarizes a new study by Ivanka Savic and Per Lindstrom, titled “PET and MRI show differences in cerebral asymmetry and functional connectivity between homo- and heterosexual subjects” and published in the Proceedings of the National Academy of Science. This is being reported widely in the press.
The abstract reads
Cerebral responses to putative pheromones and objects of sexual attraction were recently found to differ between homo- and heterosexual subjects. Although this observation may merely mirror perceptional differences, it raises the intriguing question as to whether certain sexually dimorphic features in the brain may differ between individuals of the same sex but different sexual orientation. We addressed this issue by studying hemispheric asymmetry and functional connectivity, two parameters that in previous publications have shown specific sex differences. Ninety subjects [25 heterosexual men (HeM) and women (HeW), and 20 homosexual men (HoM) and women (HoW)] were investigated with magnetic resonance volumetry of cerebral and cerebellar hemispheres. Fifty of them also participated in PET measurements of cerebral blood flow, used for analyses of functional connections from the right and left amygdalae. HeM and HoW showed a rightward cerebral asymmetry, whereas volumes of the cerebral hemispheres were symmetrical in HoM and HeW. No cerebellar asymmetries were found. Homosexual subjects also showed sex-atypical amygdale connections. In HoM, as in HeW, the connections were more widespread from the left amygdala; in HoW and HeM, on the other hand, from the right amygdala. Furthermore, in HoM and HeW the connections were primarily displayed with the contralateral amygdale and the anterior cingulate, in HeM and HoW with the caudate, putamen, and the prefrontal cortex. The present study shows sex-atypical cerebral asymmetry and functional connections in homosexual subjects. The results cannot be primarily ascribed to learned effects, and they suggest a linkage to neurobiological entities.
Past research has found that male and female brains are different, on average. This research finds that two brain measures differ based on sexual orientation: cerebral symmetry and how the amygdala functions. First, they confirm a previously reported sex differences in cerebral size asymmetry. In straight men, the right hemisphere is greater than the left and in women, they are the same size. Savic and Lindstrom find in contrast that gays are sex-atypical: the hemispheres are the same size in gay men and for lesbians, the right hemisphere is larger than the left. This is not unexpected given the previous differences in verbal skills (favoring gay males over straights) and visuospatial tasks (favoring straight males).
The amygdala is often researched in relation to the role it plays in emotion and anxiety. Recent research indicates that the right amygdala activates in men and the left in women during the processing of emotion. From these locations in the amygdala then connections are made to other regions in brain which again are different in men and women. In women, the connections may be more likely to activate emotion, whereas in men action may be the more likely result. Again, Savic and Lindstrom found sex atypical function for gays and lesbians. Gay men looked like straight women and lesbians looked like straight men, albeit the similarity was less for the lesbians.
What does this mean? The authors are cautious in their discussion and make some points which could support multiple theoretical perspectives. The authors examined aspects of brain functioning not known to be related to sexual behavior or attraction in order to reduce the possibility that sexual experience contributed to the development of the differences. In other words, it is unlikely that being homo or heterosexual caused these differences. The differences likely precede awareness of sexual orientation, according to the authors. I would agree that it seems unlikely that there is anything about sexual fantasy or behavior that could rewire the amygdala or change the size of the right hemisphere.
On the other hand, Savic and Lindstrom are not proposing that these differences cause the sexual orientation differences. Those familiar with Daryl Bem’s exotic becomes erotic theory will see how these brain differences could support his theory. It is plausible that these brain differences are involved in the gender atypical behavior so commonly and strongly associated with the development of adult homosexual orientation. Gender atypical behavior could be an associated feature of a same-sex orientation, a kind of sign of homosexual orientation or in the EBE account, gender atypical behavior and interest could predispose people to sexual regard the same sex as the other sex during pubescence.
Savic and Lindstrom propose three potential mechanisms for these differences. They note:
The mechanisms behind the present observations are unknown. In accordance with discussions about the sexual dimorphism of the brain, three factors have to be taken into account: environmental effects, genetics, and sex hormonal influences.
These are the usual suspects, genes, environment and hormones. Savic and Lindstrom dismiss genetic factors for reasons I cannot quite figure out. They say,
As to the genetic factors, the current view is that they may play a role in male homosexuality, but they seem to be insignificant for female homosexuality. Genetic factors, therefore, appear less probable as the major common denominator for all group differences observed here.
About environment, they observe that sex-based brain differences have been observed at birth and in children. However, cerebral maturation continues through puberty, especially in boys. Thus, social and environmental factors could play a role in how these differences or other differences not assessed here develop in individuals. They are not certain however and note:
However, to attribute such effects to the present results would require a detailed comprehension of how specific environmental factors relate to the four groups investigated, and how they affect various cerebral circuits. In the light of currently available information this can only be speculative.
In other words, we do not know what environmental factors could be influential on brain differentiation for male and female with sex typical and atypical brain structure and function. The authors are either unaware of Bem’s EBE theory or do not see it as relevant to their findings. Clearly, these wanted to rule out the role of sexual behavior and preference as being the driver for the differences between gays and straight that they found in their pheromone studies. Here they believe they have found clear neurological differences which in some manner relate to the differences in sexual preferences.
The authors seem more disposed to hormonal mechanisms. They discuss hormonal factors in animals, but correctly note that the relevance to humans “remains to be clarified.” They conclude:
The present study does not allow narrowing of potential explanations, which are probably multifactorial, including interplay between pre- and postnatal testosterone and estrogen, the androgen and estrogen receptors, and the testosterone-degrading enzyme aromatase. It nevertheless contributes to the ongoing discussion about sexual orientation by showing that homosexual men and women differed from the same-sex controls and showed features of the opposite sex in two mutually independent cerebral variables, which, in contrast to those studied previously, were not related to sexual attraction. The observations cannot be easily attributed to perception or behavior. Whether they may relate to processes laid down during the fetal or postnatal development is an open question.
In a post to come, I want to bring together the Langstrom et al study of Swedish twins and the Savic & Lindstrom study. We have many coming to the conclusion that brain differences confirm innate sexual orientation. However, the study of twins seems to demonstrate a role for a variety of environmental factors which operate differently for different people.
Evan
I’ve read all your posts and both of us seem to come back to one general concept.
Although gay and straight brains/bodies do appear to be different there is a 90%+ overlap between gay and straight.
So that leaves us with stuff like
A) SSA is caused by a specialized hormone, or lack of a specialized hormone
B) SSA is caused by some sort brain feminization that takes place during a short “critical period”
C) SSA is caused by a common hormone like testosterone or estrogen, however for some reason (maybe the androgen receptors are different) this hormone impacts a tiny part of the brain differently in gays and straights
Because gay and straight people are so similar it always comes back to a tiny, limited effect.
Evan
Also, one more general observation.
If SSA is due to a lack of agression or related trait why would gay men possibly have an even STRONGER sex drive than straight men? Bailey’s brain scan indicated that gay men’s brains tend to light up stronger than straight men’s brains when shown sexual images.
Drowssap,
I don’t know how attractions are caused, I examined a few possibilities according to a number of facts I know from research and everyday observation. There might be different paths at different ages that lead to similar effects during adulthood. I was mostly concerned in my messages with how same-sex attractions may work in adults, based on what this study and a few others showed with respect to some correlates, but the different paths that may lead to them at different ages, that is probably more difficult to establish. Some people got same-sex attractions before the activating hormonal effects on the brain that come with puberty, others got their attractions after puberty and after having a history of exclusive opposite-sex attractions. The GID kids may only remember feeling completely different from their peers, a lot more than many other future gay adults. So it’s a riddle how these different age groups come to the same result, even if we empirically find out how same-gender attractions actually work brainwise.
I’m not a professional to know how tiny tiny can be. There is still a theoretical possibility that not all of these correlates really have an input in creating attractions. Some may simply be the result of different hormonisation without actually having a bearing on sexual feelings. I haven’t completely discounted Catherine Dulac’s idea about the existence of a switch mechanism that is connected to the dominant sensory modality (in mice it was olfaction, in humans it must be vision) and creates attractions regardless of hormonised brain organisation differences. That is still possible, with this important qualification: in mice, the amygdala has strong connectivity with the olfactory system, whereas in humans the relevant connectivity is between the amygdala and the neocortex, particularly with the visual cortex and the prefrontal cortex, which is barely the case with mice.
That’s a very good question. I will think about that tomorrow, when I get some time. Right now I have to go and hit the hay.
Evan
My prediction:
Starting with flies and mice, and then through sheep, monkeys and finally humans it’s gonna be a simple, hormonally controlled switch. Any day/month scientists will add another animal, a little higher up the food chain to the list. That’s my guess anyway.
Drowssap,
If you’re interested in seeing Dulac’s published paper on the switch for sexually dimorphic behaviours in the female mouse, the link is here. The research paper is so thorough and suggestive that it’s awesome. You can actually see the switch diagram. Even if those results do not directly apply to humans, the idea still makes a lot of sense for mammals in general. Think about it: just like humans, female mice are the default foetal form. They are born with a brain that has circuits for both genders, but the olfactory switch suppresses the male-typical behaviours which are not useful in conjunction with a female body. The male foetus develops based on this default female foetus that already has the basic male circuitry (for aggression, thrusting, etc), but which needs to be activated by extra work done by male hormones (coming from the SRY gene on the Y chromosome). What regions exactly those male hormones need to target in order to fix the gender identity in the male foetus, that’s for researchers to zero in and for us to eventually find out. The rest of the brain could be incidentally masculinised without having as much to do with sexual behaviour as with other male-typical functions and behaviours.
Can anyone direct me to the blog where people endlessly obsess and opine on the causes of heterosexuality?
Michael,
I have addressed more than one orientation in messages 108701, 108905, 109144, 109459 and 109638. I also second your question. It would be interesting to see research done by gay scientists on heterosexuality or even sites where gay people try to understand heterosexuality, technically speaking. Different perspectives can produce new unexpected results.
Michael Bussee
When scientists figure out SSA they will figure out OSA at the same time. It’s all part of the same thing.
Evan
Right on! Thanks for the link to the study.
I think you have it 100% correct. Female type instincts are useful in biologically female bodies so they get switched on. Of course the whole point is to spread genes.
To me that’s one more reason the “gay gene survives because it boosts fertility in females” is a doomed concept.
A) What other gene is that sexually antagonistic? There isn’t one such trait in humans that I’m aware of. Correct me if I’m wrong but the Italian scientists who built that mathematical model didn’t mention any comparable trait in humans. I think that speaks volumes.
B) Women have MULTITUDES of genes that help them spread their DNA. Being attracted to men has to be one of the least important. In any case these traits are all turned off in men. Why wouldn’t this sexually antagonistic gene be turned off just like the other 1,000?
Dorrwssap commented: “When scientists figure out SSA they will figure out OSA at the same time. It’s all part of the same thing.”
Not so. Most people don’t care. They don’t even think of OSA (heterosexuality) as having a “cause” since they thnk of it as “normal”. “right”, “healthy” and “moral”.
People obsess and opine about SSA (homosexuality) because they have already concluded that it is somehow broken, disordered, sinful, sick, abnormal, immoral, etc. This is prejudice, not science.
Yes, I know there are some (very few) true scientists who approach homosexuality out of pure inlellectual curiousity, but they are the exception, not the rule. The people who trouble themselves with the “cause” of homosexuality are typically the same ones who, for religious reasons, think it can and should be repaired. The rest of us accept homosexuality as a natural human variation and get on with it.
It is a natural variation. And one that can change. If a person is not comfortable with their same sex attraction, then let them discover ways to deal with it. You may not like that. But in so doing, we find out a lot about heterosexuality as well. That is just the way it is. People can conduct themselves however they chose. Homosexuality is not the majority of the population – so people look at what makes that small difference. Same as, what makes a genius child a genius.
Can we go back to ‘it’s not a disorder, but we don’t know what it is or how it is caused’ and let scientists try to clarify a very important human dimension?
Michael,
Why are there so many gay researchers in the field of sexual orientation study? Do they have some hidden agenda if they are looking for a cause?
I said there are exceptions.
And Mary, no one thinks a genius is broken, sick or going to hell for it. As I have said many, many times before, I have NO PROBLEM with people who are unhappy being gay and want to deal with it. THAT IS THEIR RIGHT. How many times do I have to say that?
Drowssap,
You’re welcome.
The female fertility boosting hypothesis is logically circular. They propose an indirect evolutionary advantage that females might get from having homosexual males in their families, assuming that there must be at least two genes supporting the trait. After they define the mathematical models to account for their assumptions, they conclude that there are objective reasons for supporting the assumptions they built their hypothesis on.
If it’s an X-linked gene, it can get silencedin females and expressed in males who lack another copy on the Y chromosome. But this line of study has been put to trial so many times without conclusive results as yet that it’s not worth repeating until the Sanders genetic linkage study comes out.
We don’t know yet whether sexual orientation has a significant genetic component, or whether the genetic component is more decisive than the presumed hormonal influence. Camperio Ciani’s argument is based on air right now, because no gene or set of genes is known to code for sexual orientation. Actually the more recent the research the less genetic the influences appear to be. The study we discussed here, by Savic and Lindstrom, points to a whole different picture, given that the similarities have been found across genders and sexual orientations, indicating possible hormonal effects.
But there is also the newest study done by Langstrom and collegues, which argues that genetic factors take values within an 18-39% interval. So the genetic argument seems to be losing ground or to become dwarfed by other non-genetic factors.
Wait – I don’t understand. So…. you’re saying that people can look into the issue for themselves because they think they can change – but they are not allowed to call it an aberation from the norm? How then can they begin to define what they are searching for if they can only define what they know through your terms?
Michael Bussee
Except for a few kooks I think pretty much everybody accepts homosexuality. Thankfully there aren’t too many people in the world who genuinely want to hurt other people.
BUT…
Forget morality and homosexuality for a minute because it’s too close to home.
Think back and pretend you were a young, parent again. Your wife gives birth to a healthy, baby girl… but she has dwarfism. A doctor approaches you and says they have a procedure that can silence the dwarf gene and by the time she’s 5 years old she’ll look like every other girl. However before they can do this procedure the hospital has a policy that you need to get counseling from an advocate for the Dwarf community. You meet this person and he’s a good guy. He explains the important contributions that little people have made to society down through the ages. He also explains that Dwarfism is genetic and simply a natural human variation.
What would you do? Embrace this natural variation and allow your daughter to develop as a dwarf? Do you go the other way and tell the doctor to silence your daughters dwarf gene?
If you chose to silence the dwarf gene in your child does that automatically mean you hate dwarves or believe that tall people are superior? What I’m getting at is that just because scientists might find a way to understand SSA and ultimately turn it off doesn’t mean they hate gay people or believe it’s immoral.
Evan
Agreed, but I think it’s even worse than that. The Italian study was nothing more than an exercise in algebra. Their research didn’t even have to apply to SSA. That equation could work for any sexually antagonistic trait. The reality is that no, common human trait is that sexually antagonistic. If there was one, the Italians would have mentioned it in their work. I’m certainly not aware of any.
Example:
A female bone structure is 1st rate at producing babies. However 2% to 4% of men don’t have one even if they could survive just fine with girl hips.
Nothing works like that and worse yet Camperio Ciani knows it.
Can anyone direct me to the blog where people endlessly obsess and opine on the causes of heterosexuality?
LOL – I think it is the nature of the beast Michael – there are all kinds of people, on all kinds of blongs, opining in all kinds of ways about the nature of homosexuality – while all of us who are homosexual watch and smile
Evan,
I think that research must release the naked facts, no matter how uncomfortable that may be to each of us or to some of us. If the science of sexual orientation proves that male heterosexuality is the result of being, on an evolutionary scale, primarily aggressive, acquisitive, self-seeking, manipulative and lacking in awareness, I have no problem with that. Let the facts be known.
Oh, I agree with you, the problem is they haven’t truly proven anything of the sort. The fact, however, is that you latch on quickly to incredibly anti-gay ideas, and then show a complete disregard for other equally valid explanations/possibilities, etc. It is interesting listening to you
Jayhuck,
You keep saying ‘anti-gay’ ideas. What do you mean by that?
Jayhuk,
No, the question was what can you find in my messages that you think it’s ‘anti-gay’.
Sorry – that’s probably not very helpful – you latch onto ideas that are not only degrading to gay people, but that always seem to paint gay people, gay couples, and gay families in a bad light. You also seem to completely ignore the fact that other anti-gay interpretations that try to explain the results of different studies.
Anti-gay – without having a dictionary in my hands – is anything that disparages gay people, gay couples, or gay families. – a broad definition, yes – but also fairly accurate
Let’s go for the textbook definition then:”
Anything in your posts that:
“Anti-gay can refer to activities which fall into any (or a combination) of these categories:
* Prejudice in the forms of
o Homophobia – a fear or hatred of or, more generically, antipathy toward homosexuals
o Heterosexism – discrimination against and social intolerance toward homosexuals
* In a political sense
o An opposition to the perceived gay agenda, which can include same-sex marriage, gay rights and related topics.
o Specific opposition to an LGBT issue or person.
”
I’ll let you be the judge for now Evan – if you desire for something more specific, I’ll help you out with that after I’ve had a chance to sleep – buenos noches
Jayhuck,
All my messages start from arguments, not from ideologic premises. Do you label some of those ideas ‘anti-gay’ because there can rationally exist arguments like that? Is any rational argument that does not fit a partisan take on an issue anti-something? It’s like you argue for a priori impossibility of rational arguments that would not serve any given ideology.
Evan,
I simply find it interesting that all your “arguments” seem to fit certain ideological premises – whether you claim they begin there or not – that’s all
The issue isn’t that you seem to be a partial, objective scientific inquisitor, the issue is that your arguments and “ideas” have an obvious anti-gay bent. Your arguments are starting to look very biased
Michael,
I’ll reiterate what probably doesn’t need to be reiterated –
There are all kinds of people on all kinds of blogs, postulating all kinds of things regarding the cause/origins of homosexuality – at some point, those of us who are homosexuals, just have to sit back and smile at all the activity – LOL
Mary: Not that I have any power to grant “permissions”, but you are “allowed” to do and say whatever you want. Why do you persist in accusing me of saying or believing otherwise? I think I have made this point many, many, many times.
You can call yourself whatever you want. You can define yourself however you choose. You can act on your lesbian feelings or decide not to. You can be celibate, completely promiscous or something in betweem.
You can call yourself straight and/or make up your own personal defintion of any word in the dictionary. You can conceptualize “change” in any way that suits you. You can paint yourself with pink and green polka-dots and stand on your head naked in a public park for all I care.
It’s not that I “like it” or don’t like it. It’s a free country. I personally do not like homosexuality referred to as illness, sickness, sin, disorder or brokeness — and I think it does great harm to many gay and lesbian people to be told that it is. But if you want to think of your gay feelings in these negative terms, knock yourself out.
Jayhuck,
Are you saying this because you don’t like where rational arguments can lead to and because you have no counterarguments? This is how it looks like. I haven’t seen you quoting references or refuting some proposed explanations by coming up with better ones. There’s nothing wrong with not doing it, but it doesn’t entitle you to dismiss other people’s efforts without addressing their arguments.
Jayhuck,
This is what you said to Evan. Do you think your comments or arguments are any different? Calling someone anti-gay is a serious allegation and not helpful. Attack his arguments, not him.
jayhuck – If you have some counter evidence to offer to Evan’s arguments then offer it. Ad hominems are not acceptable. If you have nothing to counter it besides that then, there is no need to offer a comment on this thread.
A number of the last few comments have been off topic and have been deleted. Please comment on the topic or move on to something else.
Warren,
I countered Evan’s opinions with my own opinions – look like the thread may be dead anyway.
Ann,
I did attack his arguments
jayhuck – You provided opinion but did not provide any evidence for it that I could see. Evan provided links and studies with commentary. If you have a response to the studies that counter the findings, then please use evidence from studies. Otherwise, just saying I dont agree with you doesn’t add much to a conversation.
Evan – I agree that the maternal studies right now are “what ifs.” The Sanders and UCLA studies are well designed and will likely provide us with a clearer picture.
A very interesting study was published today. Maybe the nexus with this study related to sexual orientation is a bit too general, but there are some telling similarities.
The news can be found on ScienceDaily under the title: ‘Severe Shyness? New Study Shows That Anxiety Is Likely A Long-lasting Trait.’
Briefly — a team of scientists from the University of Wisconsin-Madison studied brain activity in relation to anxious temperament. They found greater amygdala activation across many environments, even where the subjects felt safe. This is similar to what Savic and Lindstrom found in heterosexual female and homosexual male brains when the subjects were lying in a resting state and breathing. Let’s not forget the Safron et al. (2007) study, in which gay men’s brains showed greater amygdala activation than straight men’s brains on three different stimuli tests.
This pattern of activation that supports anxious temperament involved a neural circuit that was already known from studies on stress and anxiety: the amygdala, the bed nucleus of stria terminalis (BSTc), the bilateral hippocampus, and the periaqueductal gray (PAG). People who are familiar with the literature on sexually dimorphic brain regions probably remember that the BSTc was reported to be smaller in females and that the same pattern was observed in transsexuals. Another interesting thing I remember, but which is very rarely mentioned about the PAG is that it is involved in the female lordosis behaviour.
Something is atypically sensitive or insensitive in the amygdala in both sexes of the same homosexual orientation. My intuition tells me that it’s not just an isolated predisposition but also a correlation with another area that modulates aggressiveness and which in typical patterns of activation acts as a buffer to incoming stimuli, a sensory gating mechanism. Deficits in sensory gating have been known to predispose to a number of disorders involving different neural networks that included the amygdala. In homosexual women, a male-typical pattern might point to similarly expressed and modulated aggressiveness that reflects on the way the amygdala is activated and connected to other regions.
OK, I am considering getting a second degree… ;P
This is an old thread, but I didn’t know where to put this and since it has to do, in part, with the etiology of SSA, I chose this thread. on which to put it. I hope it doesn’t get lost.
I am wondering: This study I link below was begun years ago, yet I can find no record of its findings. Is this is the study to which Greg Cochran (he of the “germ theory” hypothesis) told the readers of the Gene Expression blog that Blanchard ( I guess he is a researcher in the field?) asked for the HLA types of the SSA brothers and “the bastards wouldn’t give them to him”?
Anyone know anything about the findings of this study? Perhaps I am Google-inept today, but something seems very odd.
http://clinicaltrials.gov/ct2/results?cond=%22Homosexuality%22
I