Sexual differentiation of brain and behaviour

Abstract

It is well known that the brain can develop either masculine or feminine physiological characteristics depending on the presence or absence of gonodal hormones during the perinatal period. Although the behavioral and physiological responses of the adult can be used to assay the action of gonodal hormones early in life, sex-related morphological differences have only recently been described in the brain. The problem remains however of correlating structure with function. In the rat, intracranial hormone implantation, steroid autoradiography and the direct biochemical localization of steroid hormone receptors have been used to identify the sites of hormone action. Lesions, electrophysiological recording and stimulation of some of these same areas implicate them as parts of the neural circuits subserving sexually dimorphic physiological and behavioural responses. However, it is still not known how the morphological and endocrinological sex differences in these areas are related to the behavioural and physiological sex differences. As we shall explain, the vocal control system of the songbird provides a unique opportunity to achieve this goal.