Sexual Differentiation of the Brain and Behavior: A Primer
A general theory of sexual differentiation of the brain derives from classic experiments performed in the twentieth century, which showed that androgens from the testes act early in the development to cause some regions of the male’s brain to develop differently from those in the female. Further sex differences in brain structure and function are induced also by the effects of sex hormones from both the testes and ovaries later in life. In addition, sex chromosome genes on the X and Y chromosome are expressed inherently differently in female and male brains and cause them to be different. The sex hormones create specific sex differences in brain function by regulating cell death and birth leading to sex differences in the number of neurons. Sex hormones also regulate the length of dendrites and number of synapses devoted to specific tasks. Sex hormones cause epigenetic changes with broad impact on a large number of molecular pathways. A general principle is that cellular and molecular mechanisms leading to sex differences are highly diverse, differing in each specific brain region. Moreover, in humans the effects of gendered environments interact with multiple biological factors to produce brains that are not necessarily uniformly masculine or feminine, but a unique mixture in each individual.