It is well known that the class of steroid hormones known as estrogens have powerful effects on organs related to reproduction such as the uterus and the breast. What is less well known is that estrogens also profoundly modulate brain function and behavior. Estrogens, such as estradiol, can occur in brain as the result of ovarian secretion of the hormone into the blood that then finds its way to the brain. In male vertebrates, the testes secrete androgens, such as testosterone, into the blood and this class of steroid hormones can be converted into estrogens in the brain via the action of the...