This study is concerned with the influence of external environment upon the developing organism's internal environment and with the consequences of such influences upon subsequent maturation and adaptation. Effects of sensory stimuli on neuronal development (assessed by dendritic spine development, electrophysiologically and biochemically) at critical periods of central nervous system development will be made and evaluated with regard to subsequent behavioral and biological response. These studies will examine the hypothesis that local environment around developing neurons is modified by environment, that the nature of the modification is determined to some extent by the hormonal milieu, and that these modifications become quantitatively and qualitatively manifest during subsequent development.