Bilateral striatal lesions impair retention of an operant test of short-term memory

It has been previously shown that lesions of the dorsal striatum can disrupt performance on a variety of cognitive tasks related to prefrontal cortex function. In order to extend these studies, we have compared the effects of bilateral striatal lesions on retention of an operant test of short-term memory using a delayed matching to position task. Rats were initially pretrained on the matching task. Then, one group of animals received ibotenic acid lesions in the dorsal striatum and a second group received sham lesions. The striatal lesions induced marked deficits on delayed matching performance when the rats were retested one week following surgery. The delay-independent pattern of deficit observed does not suggest a primary impairment in short-term memory function. The lesion induced deficits were temporary, with recovery seen in the lesion group back to a control level of performance in 2 additional test sessions 5 and 10 weeks post-lesion. A follow up study investigating the time course of the deficit suggests that the recovery seen in performance measures cannot be attributed to the elapse of time per se, but rather is due to re-learning. In addition to the performance deficits in the operant task, the lesioned rats exhibited marked nocturnal locomotor hyperactivity. The results indicate that bilateral striatal lesions induce marked deficits in retention of the delayed matching to position task. They suggest a key role for the neostriatum in the execution of pre-learned responses, but do not exclude the possibility of additional involvement in short-term memory functions under certain testing conditions.