Intriguingly, areas of the cortex that respond to pain also responded during orgasm. "Perhaps it's related to the fact that people often have pained expressions at the time of orgasm," Komisaruk says.
The amygdala, the brain's emotional center, and the hippocampus, which deals with memory, light up too. This helps explain a medical mystery: When epileptic seizures start in these areas, the electrical frenzy can triggers euphoric feelings called orgasmic auras.
Most patients find the experience displeasing. But in one published case, a 51-year-old woman said her auras were so pleasant she wouldn't consider antiepileptic drugs or surgery.
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Role of inactive regions
Holstege's group has also studied the sexually stimulated brain, and his findings suggest that orgasms are not just about how the brain lights up but also about where it shuts off.
In the late 1990s, his team recruited volunteers plus their sexual partners, who would stimulate them in the lab.
To measure brain activity, the researchers used PET scanners, which require obsessive attention to timing. The stimulators were asked to induce an orgasm in their receivers within a two-minute window, with an eight-minute advance warning. (Couples were told to practice at home first.)
Results from men and women were fairly similar, says Janniko R. Georgiadis, a neuroscientist at the University of Groningen and a study coauthor. There were several regions of activation, but the most striking result, Georgiadis says, was how certain regions in the front of the brain shut down during orgasm, especially one just behind the left eyeball. Researchers have long noticed that damage to this area -- the lateral orbitofrontal cortex -- can leave people with wildly antisocial and impulsive tendencies, including hypersexuality.
Shutdowns in the brain's prefrontal cortex appears crucial, Georgiadis adds. "It's the seat of reason and behavioral control. But when you have an orgasm, you lose control."
Regions called the temporal lobes also showed damped activity. In fact, the less activity these regions showed, the more sexually aroused the women felt. These deactivations might explain the appeal of autoerotic asphyxiation, the researchers say. Depriving a brain of blood during sex not only provides a dangerous thrill but also shuts down key brain regions, leading to addictive orgasmic euphorias.
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Unsticking the brain
