WASHINGTON, Nov. 1 -- For the first time, scientists have found a difference in brain anatomy between male-to-female transsexuals and men who think of themselves as men. Researchers focused on a small region deep in the middle of the brain, called the BSTc. Male-to-female transsexuals had BSTc regions about half the size of the same region in non-transsexual men, said Dick Swaab and colleagues from the Netherlands Institute for Brain Research and Free University Hospital in Amsterdam. The transsexuals' BSTc was as small as the same region in women. Swaab, Jiang-Ning Zhou and co-authors published their study in the new issue of the journal Nature. Researchers compared the brain structures of six male-to-female transsexuals with brains of both heterosexual and homosexual men, and found that sexual preference did not influence the size differences. Transsexuals report feeling they are trapped in a body of the wrong gender, and scientists have puzzled for years over whether any biological difference would explain the persistent feelings. 'Our study is the first to show a female brain structure in genetically male transsexuals,' said the researchers' summary of their work. Just what the BSTc does in humans is not clear, but Swaab called it 'an appropriate candidate to study' because 'the BST plays an essential part in rodent sexual behavior.' Psychology professor Marc Breedlove from the University of California in Berkeley considers the human function of the BSTc an open question. A specialist in hormonal effects on the brain who published a commentary on the Dutch research, he warned that the results show only a difference, not when or why the difference developed.
'People will say that since a part of the brain is different, it must be that transsexuals were born different,' he said. 'These results do not mean that. Period.' Hormones sweeping through the fetal brain certainly could have changed the BSTc's development so that a baby was indeed 'born different,' he said. However, Breedlove said, later parts of the transsexual experience could have influenced the development of a female-sized BSTc. What impressed him about the research was that scientists managed to find a physical difference amid the many confusing, little-understand facets of the brain. 'I have to take off my hat to them for beating the odds,' he said. The possibility that a physical difference could push people toward transsexuality 'would be a great comfort,' said Dr. Shelia Kirk speaking on behalf of the International Foundation for Gender Education in Waltham, Mass. 'Transgenderists spend the earlier part of their lives puzzling: why do I need to do this?' said Kirk, who practiced obstetrics and gynecology as a man for 27 years before retiring from medicine and adopting the name and dress of a woman. The foundation estimates that roughly one percent of the world's population, both genetic males and females, feels some urge to switch genders, at least in dress. In some parts of Europe, women who wish to be surgically converted to men outnumber genetic males who wish to go in the other direction, according to the foundation. Kirk knows of at least 50 transsexual physicians in the United States, and a good number of attorneys. 'There's an awfully high number of the transgendered among engineers,' said Kirk. They have their own support organization. Some children announce they are in the wrong kind of body as early as three to four years of age, and other people deny their impulses, marry and have children, said Kirk. Not all transgenderists choose surgical 'reassignment' as they call it. Kirk, for example, has no intention of doing so. Yet the foundation recognizes that a cluster of people elect surgery in their 20s and another cluster of people opt for surgery in their late 30s after struggling with conventional roles. Some transsexuals undergo surgical reassignment as late as their 70s and 80s.
