Delayed-Nonmatching-to-Sample Performance Is Impaired by Extensive, but Not by Limited, Lesions of the Thalamus in the Rat

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Two experiments were conducted to determine whether lesions affecting limited areas of the thalamus can impair the performance of rats on a spatial delayed-nonmatching-to-sample (DNMTS) task trained before surgery. In Experiment 1, DNMTS was not affected by lesions produced by injecting 5 μl of 1 mM N-methyl-D-aspartate into either the midline thalamus (n = 16) or bilaterally 1.0 mm from the midline (n = 16). In Experiment 2, radio-frequency lesions were made 1.0 mm lateral to the midline at 3 anterior–posterior locations that destroyed the full rostral–caudal extent of the lateral internal medullary lamina (L-IML; n = 8), or at single anterior–posterior locations that destroyed either the anterior (n = 8) or posterior (n = 8) portions of the L-IML site. Although complete L-IML lesions disrupted DNMTS performance to an extent comparable to that of another study (Mair & Lacourse, 1992), lesions that were restricted to either the anterior or posterior portion of the L-IML site had no significant effect on this task.

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