Limbic lesions and externally cued DRL performance.

Abstract Rats with bilateral lesions of the amygdala, hippocampus, or neocortex and normal animals were trained to bar-press on a DRL-20 sec schedule of reinforcement following six days of pretraining on a continuous reinforcement schedule. Half the animals in each group were given a visual cue signalling the end of the required interresponse delay period. No significant differences were found between the performance of any of the groups on the cued DRL schedule. When the visual cue was absent, however, large deficits in DRL performance were found in rats with either amygdaloid or hippocampal damage. No differences were found between the DRL performance of the amygdaloid and hippocampal groups in the uncued condition. The results suggested that rats with limbic lesions can withold or inhibit a learned response when exteroceptive cues are available but not when such cues are absent. The deficits on the uncued DRL schedule may result from an inability to utilize internal cues such as response-produced proprioceptive stimuli as cues for bar-pressing [4], or they may reflect a general learning deficit which only appears in difficult tasks.