ABSTRACT
In discussing theoretical issues based on approach/withdrawal (A/W) adjustments in behavior, Schneirla (1939; 1965) pointed out that properties of stimulation at different intensities account not only for quantitative differences, but also for qualitative differences in the adjustment to the environment. We, therefore, center our discussion on the development of a specific central nervous system (CNS) neurotransmitter system, the cholinergic system, because of its well-known role in behavioral regulation through central cholinergic processes. We consider specifically a developmental phenomenon described as a two-phase ontogenetic progression in cholinergic maturation. We also focus on a polypeptide neurotrophic factor, Nerve Growth Factor (NGF), that appears to play a specific regulatory role in such a series of developmental stages. These biphasic developmental processes may be related to stage-dependent biphasic A/W regulations.
