AbstractThis study investigated biochemical substrates of the continuous stimulation effect, i.e., the developmental phenomenon whereby continuous stimulation depresses arousal level. Neonatal rats were injected intracisternally with 6‐hydroxydopamine. Motility, heart rate, and brain amines were measured in these animals, as well as in injected and noninjected control animals, at 14 and 28 days of age in an own‐control design with and without continuous auditory stimulation. Brain norepinephrine was significantly and inversely related to the magnitude of the continuous stimulation effect and experimental‐control differences increased with age. These results indicate that an intact catecholaminergic system is necessary for the mediation of increased arousal during stimul