Effects of reversible inactivation of thalamo-striatal circuitry on delayed matching trained with retractable levers

The intralaminar thalamic nuclei are characterized by their prominent projections to striatum. Lesions of the intralaminar nuclei have been found to impair delayed matching trained with retractable levers. Comparable impairments have been observed for rats with lesions of the olfactory tubercle, involving ventral areas of striatum and pallidum. We conducted two experiments to test the functional dependence of thalamic and striatal lesions on the delayed matching task. In experiment 1, we determined the effects of inactivating the intralaminar nuclei with bilateral lidocaine infusions. In experiment 2, we compared the effects of unilateral thalamic inactivations in rats with unilateral olfactory tubercle lesions. We trained rats to perform the delayed matching task to criterion and then implanted dual cannulas aimed at the bilaterally symmetrical areas in the intralaminar nuclei. Rats in experiment 2 were also given a unilateral olfactory tubercle lesion. The results of experiment 1 showed dose-dependent impairments for bilateral infusions that were qualitatively similar, although of lesser severity than delayed matching impairments observed in previous studies for rats with lesions involving extensive areas of the intralaminar nuclei. A comparable impairment was observed in experiment 2 when thalamus was inactivated on the side opposite the olfactory tubercle lesion. Performances were significantly worse when thalamus was inactivated on the contra-lesion than on the ipsi-lesion side of the brain. These results are discussed in terms of the role of ventral striatum and related thalamic nuclei in memory.