The volunteers watched the films while being monitored by a positron emission tomograph, a device which provides extremely detailed images of the brain and can be used to identify brain regions that are activated during different mental operations.
Five brain areas were found to be more active during the sexually explicit film than during the neutral and/or comic film.
The first was the inferior temporal cortex, a region also corresponding to the visual associative zone. The researchers inferred that the subject was assessing and analyzing the visual stimulus when this zone was activated, corresponding to the perceptive-cognitive component of sexual arousal.
The second region was the right orbitofrontal cortex, which might be related to emotional and motivational phenomena.
The third area was the left anterior cingulate cortex, which appears to control primary physiological responses (endocrine and autonomic), but also affective responses, to sexual stimuli. In other words, it would govern physical and psychological preparation for sexual activity.
The fourth region was the right insula, that could be involved in subjective perception of physiological modifications associated with arousal (heart rate acceleration, penile erection, etc.)
Finally, the right caudate nucleus probably controls whether sexual arousal is followed by sexual activity.
The researchers also measured various physiological parameters, especially the blood concentration of testosterone, the principal male hormone. The testosterone level rose very strongly during the sexually explicit film; it also increased slightly during the comedy sequence. These results may throw light on the neurophysiological bases of sexual arousal dysfunctions, which may take the form of sexual apathy or, on the contrary, pathological hyperactivity leading to deviant behavior such as rape. Serge Stoleru and colleagues have already started to study men with a marked and durable loss of sexual desire.