The research proposed here focuses on the neuroanatomical and functional description of avian brain networks involved in vocal control and vocal learning. In the canary these networks show gross sexual dimorphism as well as hemispheric and hypoglossal dominance. We would like to test the generality of these observations in a taxonomically unrelated group, that of budgerigars and their allies (Psittaciformes), which show vocal learning but no hypoglossal dominance. As a separate endeavor we will conduct studies to characterize the ontogeny and describe in detail the connectivity of the vocal control network of canaries. Characteristics of these latter studies follow. In canaries the vocal control system is still developing between the 5th and 10th posthatching weeks, a time when song development is just starting. We hope to observe anatomical and functional changes in this system which can be related to hormonal variables, emerging hemispheric dominance and to the learning of song. We will also scrutinize brain vocal areas for evidence bearing on information of synapses, formation of dendritic spines, and measureble changes in size and shape of dendritic fields. For this we will use histological techniques supplemented, whenever possible, by neurophysiological methods. Electrophysiological studies of single units will serve to identify and map the occurrence of excitatory and inhibitory connections. Evoked field potentials will be used for accurate placement of small lesions to assess behavioral effects and to map the functional subdivisions and connectivity of identified vocal areas. The same neurophysiological and neuroanatomical methods will also be used to assess the nature of changes occurring at the time of induced reversal of hemispheric dominance, and following castration and testosterone therapy. We hope to identify age, hormonal and experimential variables that might set limits to the observed plasticity of the brain's vocal control networks.