Orgasm in the Brain, or Porn for Neuroscientists

Sometimes I really think I went into the wrong area of cognitive science. I mean, I'm not really a big fan of cognitive neuroscience; I tend to think it's a faddish discipline that tells us little more than that cognition happens in the brain (a joke that I stole, but since none of you are likely to know the person from whom I stole it, and since he probably isn't reading this, I'm going to pretend it's my own). But when I read about studies like the one I'm about to describe, my opinion of imaging research changes dramatically, not so much because I think it's more scientifically sound, but because I would really like to run the experiments.

The research, which I discovered through John Hawks (my new source for all things cool and neuroscientific), involves looking at the brain regions that are active during sexual arousal and orgasm. The article that John links in his post is mostly about a study on female orgasms, and more specifically on the differences between the brain areas that are active during faked and real female orgasms. That research is so new that I can't find it on any of the article databases that I usually use. The research on male orgasm, however, was published a couple years ago, so I can talk about that^*.

Here is the background: several studies of brain activation, or dysfunction as a result of brain lesions, during ejaculation have been conducted using rats, along with at least one study using nonhuman primates. These studies have been inconclusive with regard to the specific functions of different brain regions during ejaculation, and there are differences between the activation in rat and primate brains. These two facts limit our ability to draw conclusions about brain activation in human males during ejaculation from the animal literature. Now that we have some fairly good imaging techniques (in particular, fMRI and positron emission tomography, or PET), though, we can look at brain activation in humans during ejaculation directly, and bypass the animal literature altogether.

How, you might ask, do we get people to ejaculate while in a PET scan machine? Well, that's where this research gets interesting (for me, at least), and what makes me think I should have gone into the neuroscience of sex. Here is the description of the experiment, from the methods section of the above-linked paper:

The volunteers were asked to perform the following tasks twice: rest, erection, sexual stimulation, and ejaculation induced by sexual stimulation. To minimize motor activity by the volunteer during the scan, sexual stimulation was provided by his female partner by means of manual penile stimulation in the tasks stimulation and ejaculation. Manual stimulation was continued throughout ejaculation. The volunteer's head was maintained in position with a head-restraining adhesive band, and, to minimize visual input, volunteers were asked to keep their eyes closed.

Seriously, does this not sound like neuroscientist porn (complete with bondage)? If sessions were taped, how much do you want to bet that the videos are currently being sold on some neuroscience email group? Anyway, in order to make sure that the volunteers could perform the task, it was suggested that for a few weeks prior to the experimental session, they practice at home, "especially regarding minimizing head and limb movements." So the experiments were probably fun for the participants as well.

Once they had them in the machines, they took scans during stimulation and during orgasm, and later analyzed the data by comparing the stimulation scans to orgasm scans in 11 volunteers (only 8 of the 11 could be used for some analyses, for reasons discussed in the paper that are simply too uninteresting to mention in a blog post).

Most of the results are unsurprising. They found the strongest activation during ejaculation in the mesodiencephalic transition zone (MTZ), which is comprised of several regions involved in the brain's rewards system, and its dopamanergic reward system in particular. Specifically, the ventral tegmental area is part of the MTZ, and is associated with the pleasurable sensation people get from drugs like heroin and cocaine. Thus, orgasm and heroin highs appear to use the same brain structures in males. Activation was also found in the right thalamus and neighboring regions, which are associated with arousal and "visceral sensory responses." The right parietal lobe, which is also associated with sensation, was also active during ejaculation. All of this sounds about right. The same goes for the activation found in certain parts of the visual system, including the precuneus (visual memory) and the secondary visual cortex, because as the authors note, most of the volunteers reported using visual imagery during the session.

Finally, and perhaps this is a bit surprising, they found a lot of activation in the cerebellum. Traditionally, the cerebellum has been thought to be primarily involved in movement, but the volunteers' movements were restricted, and their female partners were doing all of the work. Recently (over the last decade or so), researchers have begun to realize that the cerebellum is involved in a lot more than just movement, though. In particular, it appears to be heavily involved in emotion, and the authors of the article explain its activation by arguing that cerebellum activity during ejaculation produces a "rush" similar to that experienced during other rewarding activities, such as heroin use and listening to pleasant music.

The researchers did find deactivation in two areas, the amygdala and entorhinal cortex. These areas, especially the amygdala, are also associated with emotion. The amygdala is particularly associated with fear responses, and decreased activation in this area has been shown to cause euphoric states associated with drug use and intense love. So, the corresponding activation of the cerebellum and deactivation of the amygdala appear to cause the intense euphoric emotional state associated with orgasm.

Thus, in sum, human male brain activity during orgasm looks a lot like it does when we're doing drugs. The authors also note that it also looks more like nonhuman primate activation than rat activation, a fact which probably ruins a lot of potential jokes. Furthermore, the bulk of the activation during ejaculation was in the right hemisphere, which makes me wonder whether left-handers have stronger orgasms (a speculation that is completely unwarranted by the data, but I'm pretending to be a cognitive neuroscientist now). Mostly, though, given the terrible resolution (both spatial and temporal) of the imaging techniques that are available today (both PET and fMRI were used in this study), what we've really learned is that male orgasm causes brain activation. The authors themselves note that the resolution isn't sufficient to distinguish the activation in different parts of the MTZ, and it's hard to say exactly which of the functions of the other multi-functional brain areas are involved, because we can't tell exactly which parts, much less which neurons, are active. As is usually the case with brain imaging studies, the conclusions involve inferences to the best theoretical bias. Still, we've got to start studying the role of the brain in male orgasm somewhere, sometime, and even if I don't think this sort of research tells us a whole hell of a lot, I sure wish I could get in on it.

^* Just in case you're new to the blog, or you've forgotten, it's my policy not to comment on research that I only know about through articles in the popular press, because the press generally does a horrible job of reporting about science, especially cognitive science.