Summary

Dutch scientists led by Dick Swaab measured a tiny area deep in the brain called the BSTc. It was larger in men than in women, and in six trans women who had died it was the size usually seen in women. Published in Nature, the study became the best-known evidence for the idea of a 'female brain in a male body'. The evidence is thin. There were only six trans brains, all from people who had taken estrogen and testosterone-blocking drugs for years, and most had had their testes removed. So hormone treatment, not something present from birth, could explain it. A follow-up by the same group (Chung et al., 2002) found the male-female difference in this area does not develop until adulthood, long after most gender distress begins. No independent team has repeated it. It is an unconfirmed observation, not proof of an inborn gender identity.

Key findings

• 연구는 특정 신경 섬유를 표시하는 염색을 이용해 사후 기증된 뇌에서 BSTc라는 작은 뇌 영역의 크기를 측정했습니다.
• 비교 뇌에서 이 영역은 남성이 여성보다 약 44% 더 컸습니다.
• 이성애자와 게이 남성은 크기에 차이가 없었으며, 저자들은 이를 그 차이가 성적 지향과 관련이 없다는 뜻으로 받아들였습니다.
• 트랜스 여성 6명에서는 성별 감정이 일찍 시작되었든 나중에 시작되었든 이 영역이 여성 크기였습니다.
• 저자들은 비정상적인 성인 호르몬 수치를 가진 몇몇 비트랜스 환자가, 성인 호르몬이 이 영역의 크기를 설명하지 않는다는 것을 보여준다고 주장했습니다.
• 트랜스 여성 6명 모두 에스트로겐과 테스토스테론 차단 약물 사이프로테론 아세테이트로 치료받았고, 한 명을 제외하고 고환을 제거했습니다(Breedlove, Nature 1995).
• 같은 그룹의 이후 연구는 이 영역의 남녀 차이가 성인기에야 나타난다고 밝혔고(Chung, De Vries & Swaab, J Neurosci 2002), 이는 이 영역이 어린 시절에 시작되는 성별 감정을 일으킨다는 생각을 약화시킵니다.

Abstract

Transsexuals have the strong feeling, often from childhood onwards, of having been born the wrong sex. The possible psychogenic or biological aetiology of transsexuality has been the subject of debate for many years. Here we show that the volume of the central subdivision of the bed nucleus of the stria terminals (BSTc), a brain area that is essential for sexual behaviour, is larger in men than in women. A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation. Our study is the first to show a female brain structure in genetically male transsexuals and supports the hypothesis that gender identity develops as a result of an interaction between the developing brain and sex hormones.

Conclusion

The authors concluded that the BSTc is sexually dimorphic in humans (larger in men), that male-to-female transsexuals have a female-sized BSTc, and that this difference was not explained by adult sex-hormone levels or by sexual orientation. They presented it as the first evidence of a female brain structure in genetically male transsexuals, supporting the hypothesis that gender identity develops from an interaction between the developing brain and sex hormones.