Performance on a differential reinforcement of low-rate schedule in neodecorticated rats and rats with hippocampal lesions

Abstract

Rats with total removal of neocortex (neodecorticates), hippocampectomized rats (hippocampals), and their controls were trained on a differential reinforcement of low-rate 12-sec (DRL12) schedule. With training, neodecorticates reduced the frequency of short interresponse times (ERTs) and increased the frequency of longer IRTs. They also significantly reduced the interresponse time per opportunity ratio for short IRTs and significantly increased the ratio in the period following reinforcement availability. Between-group differences on measures of IRT distribution, IRT per opportunity, and postreinforcement delay suggest separate contributions by neocortex and hippocampus to observed behavior on this task. Performance deficits in the lesioned groups are interpreted in terms of the associative power of the predictive lever increasing the pressure to respond in neodecorticates and the possible loss of place learning in both neodecorticates and hippocampals. In conjunction with previous work, these results indicate that temporal sensitivity in the rat is not destroyed by total neodecortication.