Effects of thalamic lesions on repeated relearning of a spatial working memory task.

Anterior thalamic (ATN) dysfunction produces memory deficits in rats and humans. The current study shows that, with a substantial delay between post-surgery tests, controls show repeated relearning on a spatial working memory task whereas rats with neurotoxic ATN lesions showed repeated relearning deficits. Rats were pre-trained to criterion, but not over trained, on the spatial task. ATN lesions produced the expected spatial memory and relearning deficits about two weeks post-surgery and again either one or 15 weeks later. Control rats also showed forgetting post-surgery and after a 15 week break, relearning the task on each occasion. Controls with only a 1 week break before their final re-test showed negligible forgetting. Thus, a short break between re-tests replicated previous findings with ATN lesions, but a long break allows repeated comparison of rates of learning from a common starting point in sham and ATN-lesioned animals, providing a useful paradigm for future testing of pro-cognitive treatments.