Neural activities of various brain structures were examined during the acquisition and omission of a behavior. Forty-one rats were used. The positive reinforcer was the stimulation of the lateral hypothalamus, the effectiveness of which had been controlled in advance using the self-stimulation procedure. As original training, head movement during the presentation of an auditory signal was rewarded with the stimulation of the lateral hypothalamus. Following the acquisition of the behavior, omission training was given, during which inhibition of head movement was rewarded. In each session, multiple unit activity for 1 sec prior to the onset of the tone was compared with that during 1 sec tone presentation. In both training sessions, increases in unit activity to the tone, associated with the acquisition of the correct response, were found in the dorsomedial thalamus and the ventral tegmentum. In contrast, the neurons in the prefrontal cortex showed an increased response to the tone only during the omission training. These results suggest that the dorsomedial thalamus and the ventral tegmentum are related to the acquisition of the stimulus-reinforcer contingency, while the prefrontal cortex is related to behavioral inhibition in the omission learning.