The effects of ibotenic acid lesions of the nucleus accumbens on spatial learning and extinction in the rat.

Rats with ibotenic acid lesions of the nucleus accumbens (N. Acc) were studied in two spatial learning paradigms: a T-maze and a Morris water maze. Learning of a spatial discrimination task and its reversal in the T-maze were disrupted by the N. Acc lesions. As both original and reversal learning were impaired, there was no evidence of a specific lesion effect on reversal learning. The lesioned rats did not perseverate excessively in their choice of the previously reinforced arm. There was evidence of behavioural inflexibility during extinction when the lesioned rats failed to slow the pace at which they ran the maze in the absence of reward. Spontaneous alternation was not significantly affected by the lesion. Acquisition of the second spatial task, locating the hidden platform in the Morris water maze, was also impaired. The lesioned rats did eventually learn the task and successfully reached the platform with similar latencies and heading errors to controls. Thus, the N. Acc lesion impaired but did not abolish spatial learning in the T-maze and the water maze. The deficits observed in this study may reflect a role for the N. Acc in the reorganisation of behaviour in response to external change.