THALAMIC AMNESIA RECONSIDERED - EXCITOTOXIC LESIONS OF THE INTRALAMINAR NUCLEI, BUT NOT THE MEDIODORSAL NUCLEUS, DISRUPT PLACE DELAYED MATCHING-TO-SAMPLE PERFORMANCE IN RATS (RATTUS-NORVEGICUS)

Rats with large thalamic lesions affecting the mediodorsal (MDn) and i ntralaminar (ILn) nuclei are impaired performing delayed matching to s ample tasks (DMTS). To determine the neurological basis of this defici t, we trained rats to perform a place DMTS task and then compared the effects of excitotoxic lesions of the MDn, the ILn, and the lateral in ternal medullary lamina (L-IML). The MDn lesion had little effect. The ILn group was significantly impaired throughout 8 months of training. The L-IML group exhibited an intermediate level of impairment. Varyin g the sample response requirement, retention intervals, and trial-to-t rial congruence in the side reinforced, had predicted effects, as did variations in response latency. However, none of these factors interac ted with the treatment effects. These findings indicate that DMTS perf ormance is disrupted by lesions of the ILn but not the MDn.