Many of you will be shocked -- shocked -- to discover that ejaculation turns off men's brains. Well only briefly...

Janniko et al., after publishing an earlier paper on the subject in 2003, have chosen again to examine the activation in the male brain during ejaculation. They use PET scanning -- a technique that measures the metabolic activity of different parts of the brain.

Why a further paper on the subject, you ask? Did they not answer all the important questions in the prior paper?

Well unfortunately the early study had what we scientists like to refer to as a methodological problem. You see PET scans usually integrate a signal from the brain over a two minute time window. Unfortunately, the male orgasm does not typically last for two minutes -- unless some of these people are having sex way, way more interesting than mine -- so the researchers felt the need to correct their earlier data using a shorter time window.

The funniest part of this paper is how they describe this problem. Here is the introduction:

In 2003, we reported on ejaculation-related brain regions, identified with [15O]-H2O positron emission tomography (PET). Single, short-lasting, more or less randomly occurring events like ejaculation, however, are not commonly investigated with [15O]-H2O PET and provide a methodological challenge.

Single, short-lasting, and more or less random -- a summary of ejaculation if I ever heard one.

In conventional [15O]-H2O PET, data are usually integrated over a 90-120 s-period, during which an experimental task is performed continuously. With single, short-lasting events the task is less homogenous over the course of the scan, which reduces the statistical power. In addition, it puts constraints on the timing of the event, because of different sensitivities within the scan owing to radiotracer dynamics.

I am just visualizing the researcher talking to the guy in the PET scanner: "Um Sir. Do you think you could spread this out over two minutes? I mean, we would really like something homogenous over the length of the scan..."

Therefore, we used a customized methodological approach to investigate ejaculation-related brain activity: we ensured that ejaculations occurred within a fixed time window and, to enhance the specificity, we selected only 20 s of data around the moment of ejaculation. Following this approach we found abundant activation, primarily in the midbrain, the thalamus, the striatum, and the cerebellum, but also in parts of the neocortex. This methodological approach, however, could not be validated at the time.

Maybe this is just perversity on my part, but how exactly did they ensure that it happened during a fixed time window? Selective porn exposure, perhaps.

Anyway, the researchers appear quite pleased that they have overcome these astonishing technical hurdles. They can now say with assurance that the areas activated and deactivated in the male brain during ejaculation are as the graphic below illustrates. (The left is activations; the right is deactivations. Click to enlarge.)

As indicated in the title of this post, large swathes of the frontal cortex -- where most of the higher brain functions such as say reasoning take place -- are in fact deactivated during ejaculation.

No word on whether these deactivations persist, but I wouldn't ask a guy anything important for several minutes afterwards. You know, just to be safe...