Science File / An exploration of issues and trends affecting science, medicine and the environment : Small Area of Brain Controls Sexual Identity, Study Suggests

Men who believe that they are women trapped in a male body may be at least partially correct, according to a new study in the journal Nature. A team from the Netherlands found that sexual identity may be controlled not by body shape, but by a small portion of the hypothalamus called the bed nucleus of stria terminalis, or BST.

Autopsies showed that this area of the brain, which has previously been linked to sexual activity in animals, is about 31% larger in men than in women. But in the brains of six male-to-female transsexuals, the BST was the same size as it is in women, perhaps leading to their perception of themselves as women. The size of the BST was independent of sexual preference or hormone use. Dr. Dick F. Swaab of the Graduate School of Neurosciences in Amsterdam said the BST appears to be part of a larger brain network that makes a man feel like a woman.