Orgies alter the brain

New Scientist, 25 October 1997
ALISON MOTLUK

EXCESSES of sexual indulgence or abstinence can change the structure of the brain, says a scientist in California. Marc Breedlove of Stanford University put 10 male rats in with females given hormones to make them respond readily to male advances. Nine other males were caged with females treated to rebuff their attentions.

After a month, he examined a part of the male rats' brains called the bulbocavernosus, which is active during copulation. The motor neurons -- a category of nerve that controls muscle fibres -- were significantly smaller in this area in the males who had gorged on sex than in their celibate counterparts, reports Breedlove in this week's Nature(vol 389, p 801). Hormone injections made sure that all the male rats had the same levels of male hormones, so the differences were presumably linked to the act of copulation itself.

Breedlove isn't exactly sure what his findings mean. Smaller motor neurons fire more frequently, he notes, so they may be primed for further action. "Or perhaps their smaller size reflected ill heath after overuse."

But the take-home message, says Breedlove, is that the structure of the brain and behaviour can modify one another. "The brain not only controls our behaviour but is altered by our experience," he says.