Effects of dorsal and ventral striatal lesions on delayed matching trained with retractable levers.

Recent evidence has suggested that thalamic amnesia results from damage to the intralaminar nuclei, an important source of input to striatum. To test the hypothesis that intralaminar damage disrupts functions mediated by striatum, we studied the effects of striatal lesions on a delayed matching task known to be affected by intralaminar lesions. Rats were trained to perform the task and given one of five treatments: sham surgery or a lesion of medial or lateral caudate/putamen, nucleus accumbens, or ventral striatum. Rats with ventral striatal lesions were impaired compared to all other groups. Rats with medial caudate/putamen or nucleus accumbens lesions were impaired compared to controls. The effects of ventral striatal lesions were sufficient to account for impairments in the accuracy and latency of delayed matching responses observed in previous studies of intralaminar and medial frontal cortical lesions. The ventral striatal lesions involved portions of ventral pallidum and thus it seems likely that they affected functions mediated by the nucleus accumbens as well as striatal areas of the tubercle. Serial reversal learning trained in the same apparatus with the same reinforcer was unaffected by all of the lesions. These results are discussed in terms of the roles of midline thalamic nuclei and of thalamo-cortico-striatal circuits in delayed conditional discrimination tasks.