Reference Work Entry

Neuroscience in the 21st Century

pp 2973-2998

Sexual Differentiation of the Human Brain in Relation to Gender-Identity, Sexual Orientation, and Neuropsychiatric Disorders

  • Dick SwaabAffiliated withNetherlands Institute for Neuroscience Email author 
  • , Ai-Min BaoAffiliated withDepartment of Neurobiology, Zhejiang University School of Medicine, Key Laboratory of Medical Neurobiology of Ministry of Health of China


During the intrauterine period, a testosterone surge in boys masculinizes the fetal brain, whereas the absence of such a surge in girls results in a feminine brain. Since sexual differentiation of the genitals takes place much earlier in intrauterine life than sexual differentiation of the human brain, these two processes can be influenced independently of each other. Gender identity (the conviction of belonging to the male or female gender), sexual orientation (hetero-, homo-, or bisexuality), pedophilia, and the risks for neuropsychiatric disorders are programmed into our brain during early development. There is no proof that postnatal social environment has any crucial effect on gender identity or sexual orientation. We discuss the relationships between structural and functional sex differences of various brain areas and the way they change along with changes in the supply of sex hormones on the one hand and sex differences in behavior in health and disease on the other.