External cue control of DRL performance in rats with septal lesions

Abstract

Abstract Septally-lesioned, thalamically-lesioned, and normal animals were trained to bar-press on a DRL-20 schedule for food reinforcement. For half of the animals, a cue light signalled the end of the required delay during the first half of training. The light cue conditions were reversed for all animals in the last half of training. All animals decreased their rate of response during training, regardless of the presence or absence of the cue light. However, the septal animals, in contrast to the normal and thalamic animals, increased their reinforcement frequency only when the cue light was used. In addition, when the cue light was used, all animals had a bimodal distribution of inter-response times, with one mode at the shortest recorded delay and a mode at the 20-sec delay interval. When the cue light was not used, the thalamic and normal animals again had a bimodal distribution, while the septal animals had a unimodal distribution with the mode located at the shortest recorded delays. The results suggested that the cue light functioned as a discriminative cue for bar-pressing and secondly, as a reinforcing stimulus for behaviors which mediated the required delay. It was concluded that the septal deficit on DRL schedules results from a failure to utilize response-produced, proprioceptive stimuli as cues for bar-pressing.