Septal lesions in rats and the acquisition of free-operant successive discriminations

Abstract

In Experiment 1 septal and control rats received both preoperative and postoperative baseline training on food reinforcement VI schedules in the presence of two successively presented stimuli before responding was extinguished in the presence of one of the stimuli (S-). The septals showed: (1) higher asymptotic response rates in the S- stimulus; (2) higher terminal baseline response rates; and, (3) larger magnitudes of behavioral contrast. When the baseline rates of septal and normal rats were equated, the persistent responding in the S- stimulus remained whilst the difference in contrast was eliminated. In Experiment 2 it was found that if animals could perform a response in the S- stimulus which switched the stimulus and the reinforcement contingencies to those associated with S+ stimulus, then septal rats showed a higher terminal level of discriminative performance in terms of this response than controls. It is concluded that septal persistence represents a failure of response inhibition rather than a deficit in the ability to register or associate information about the withdrawal of reward and that the septal change in the magnitude of contrast is related to the elevation of the baseline response rate rather than to the occurrence of response persistence.