NeuroImage has a study in press presenting fMRI activations that depend upon sexual orientation. It is not the first study to show this, but this time, lesbian women's brains react too, and most importantly, the ventral premotor cortex, supposed to shelter the world-famous mirror-neurons, reacts differently in gay and straight subjects. Since the stimuli used were aroused sexual organs, this has led some (like Jonah Lehrer who has a post about it) to suppose that pornography might rely on a mirror-neuron system: you like what you see because a motor-resonance mechanism makes you think you're doing it. I argue that this is not so; I have an idea for an experiment that would prove my point.

It is not the first time an fMRI study evidences “a functional endophenotype for sexual orientation in humans”, that is: brain areas that react differently to certain stimuli in gay and straight people. Last year, I. Savic and his team showed that women and homosexual men were sensitive to (putative) masculine pheromones, whereas men were not. The gay group was a control: the chief interest of the study was to prove that humans were not insensitive to pheromones (as was then believed). Nevertheless, these results enjoyed a huge and unexpected success among gay groups. Even though its intellectual apparatchiks, still intoxicated with Butler, Foucault and Derrida, refuse to consider the possibility of a biology of homosexuality (at least in France), this bodes well for the future acceptance of neuroscientific findings by the gay movement.

In the NeuroImage paper, German sexologists presented homo- and heterosexual men and women with pictures of aroused male and female sexual organs (the stimuli are not shown in the paper). Thereagain the gay groups were controls, meant to exclude the possibility that the subject might only be reacting to the sight of a member of the other sex. Some brain areas in straight men and lesbian women reacted more to female genitalia than they did in straight women and gay men (and the reverse is also true). The most puzzling fact about these differential activations is that some of it was found in the ventral prefrontal cortex (PMv). A majority of neuroscientists agree that some activities found in the PMv can be attributed to a very peculiar bunch of neurons discovered in the macaque brain. These are mirror-neurons and canonical neurons (see about them both the AlphaPsy primer on mirror-neurons).

There are three possibilities.

(1) It might be that there is no motor activation at all and that what was observed was silent verbalisation ("now that's a nice *****!!" vs. "So what? Another boring *****..."). After all, we're in the language areas; but the fact that the activation is bilateral speaks in disfavour of this view.

(2) Mirror-Neurons could cause the activation. This would be exciting, since It would add one more social skill to the (already plethoric) proto-social repertoire of mirror-neurons (see an entertaining movie describing it). But I do not think that it is the case, since mirror-neurons require, in order to be activated, the observation of a goal-directed action. Since no such thing was presented to the subjects, it would be a very strange brand of mirror-neurons that would fire in these conditions.

(3) Canonical neurons could cause the activation. This is more plausible to me; canonical neurons are activated when we do things (e.g. grasping a frying pane) with objects, and when we see these objects without touching them. Canonical Neurons are much less investigated than their elder brothers, but there is at least one very nice study by Julie Grèzes that shows a form of canonical activity in humans. To show that the activation observed in the NeuroImage study is indeed canonical, all you have to do is present the subjects with pictures of aroused genitalia photographed from the point of view of the genitalia's proud possessor. This kind of change in point of view may seem trivial, but it is known to impact significantly on mirror and canonical activity.

If canonical neurons are responsible for the NeuroImage study activation, female genitalia, viewed from the point of view of their possessor, won't produce any activation in men, gay or straight (and the reverse will be true for women), since none of them is used to manipulate them fom such a position (at least, not frequently); If mirror neurons are responsible, on the other hand, one should reproduce the results of the NeuroImage study.

This would do justice to the often disregarded canonical neurons, the neglected youngsters of the premotor family. And it would confirm the law according to which younger brothers are gay.

Last minute: Chris at Mixing Memory and The Neurocritic have posted about this study. The Neurocritic is particularly sharp and funny. Everyone seems to be complaining about the fact that the stimuli aren't shown; hey, NeuroImage guys! it's not too late!