Acquisition and retention of negative patterning in hippocampal-lesioned rats

Abstract

In this series of experiments, we examined whether animals with aspiration lesions of the hippocampus could retain a negative patterning task learned preoperatively (Experiment 1) or acquire a negative patterning task postoperatively (Experiment 2). In a negative patterning task, each of two single cues is followed by an unconditioned stimulus (A+, B+), while the two cues presented together are not followed by the unconditioned stimulus (AB- ). Rats were exposed to a novel context and allowed to drink a saccharin solution for 15 min on AB- trials. On A+ trials, the rats were exposed to saccharin alone, and on B+ trials, the rats were exposed to the novel context with a water bottle and were given an injection of LiCl in both cases. The rats showed aversions to the context and saccharin alone but consumed large amounts of the saccharin when the two cues were presented together. While hippocampal-lesioned rats showed some deficits on retention tests, they showed good acquisition of the negative patterning task.