Retrograde amnesia in rats with dorsomedial thalamic damage.

The present research addresses the effects of dorsomedial thalamic lesions on remembering a delayed alternation problem learned before damage. Male rats were trained on a delayed alternation task. Successful performance of the test first required learning of the general principle that Go and No Go trials alternate with each other and, second, in every trial, recalling the specific consequences of the responses in the previous trial after a relatively short or long interval. The animals which had reached the learning criteria were paired by the learning level shown during the training and assigned semi-randomly to one unoperated control and one dorsomedial thalamic lesioned group. Lesions of the dorsomedial nucleus of thalamus produced a moderate and transient impairment of remembering of the delayed alternation learned before the damage for delays ranging from 0 to 40 s, and a severe impairment of the postoperative performance when delays were increased to 80 s. Detailed analysis of the animals' performance throughout the postoperative retraining confirms the role of the dorsomedial nucleus of the thalamus in memory and suggests that this thalamic region plays a role in recalling specific response-related events. Further research concerning the extension of retrograde amnesia associated with thalamic damage and the nature of the memory loss is proposed as necessary.