THE EFFECTS OF SELECTIVE LESIONS WITHIN THE ANTERIOR THALAMIC NUCLEI ON SPATIAL MEMORY IN THE RAT

Groups of rats received cytotoxic lesions centred in either the anteri or medial thalamic nucleus (AM), the anterior ventral and anterior dor sal thalamic nuclei (AV/AD), or all three nuclei combined (ANT.T). The se lesions were made by injecting N-methyl-D-aspartate acid (NMDA). Th ese rats, and a group of surgical controls (SHAM), were trained on a r ewarded forced-alternation task in a T-maze. While the selective AM an d AV/AD lesions produced an initial acquisition impairment, only the a nimals with combined lesions (ANT.T) showed a persistent deficit throu ghout the 16 acquisition sessions. Subsequent testing with a cross-maz e confirmed that the SHAM, AV/AD, and AM groups were able to use alloc entric cues, while the ANT.T group were impaired. In contrast none of the three anterior thalamic groups were impaired on a subsequent egoce ntric discrimination and reversal task run in the same apparatus. A fi nal test using the eight arm radial-maze, revealed marked deficits in the ANT.T group as well as milder deficits in the AV/AD group. The res ults from these experiments help to confirm the importance of the ante rior thalamic nuclei for allocentric tasks, but suggest that no region is pre-eminently important. The findings also help to account for oth er studies which have reported that anterior thalamic lesions have see mingly mild effects on tests of spatial memory.