The role of different nuclei of the thalamus in processing episodic information.

Male rats received either electrolytic or sham lesions bilaterally into the dorsomedial nucleus or the anterior nuclei of the thalamus or were assigned to an unoperated control group. After the postoperative recovery period all lesioned and control animals were tested for the ability to master a delayed alternation task. It was characterized by the alternation of Go and No Go trials, which were separated by intervals ranging between 0 and 80 s. Its successful performance required, firstly, the learning of the general principle that Go and No Go trials alternate with each other and secondly, in every trial, recalling the specific consequences of the responses in the previous trial after a short or long delay. Bilateral damage of the thalamus including the dorsomedial nucleus or anterior nuclei severely disrupted the performance of a delayed alternation task. A detailed analysis of the performance throughout the training suggests that the impairment associated with both thalamic lesions could be interpreted as a deficit in recalling specific information. This analysis also reveals a failure in the early stages of learning. Further research concerning the role of the dorsomedial nucleus and the anterior nuclei of the thalamus in learning and memory is proposed as necessary.