The Intralaminar Thalamic Nuclei Contribute to Remote Spatial Memory

Recent studies have shown that the anterior (ATN) and lateral thalamic nuclei (including the intralaminar nuclei; ILN/LT) play different roles in memory processes. These nuclei have prominent direct and indirect connections with the hippocampal system and/or the prefrontal cortex and may thus participate in the time-dependent reorganization of memory traces during systems-level consolidation. We investigated whether ATN or ILN/LT lesions in rats influenced acquisition and subsequent retrieval of spatial memory in a Morris water maze. Retrieval was assessed with a probe trial after a short (5 d, recent memory) or a long (25 d, remote memory) postacquisition delay. The ATN group showed impaired acquisition compared with the Sham controls and ILN/LT groups, which did not differ during acquisition, and exhibited no preference for the target quadrant during the recent or remote memory probe trials. In contrast, probe trial performance in rats with ILN/LTlesions differed according to the age of the memory, with accurate spatial retrieval for the recent memory probe trial but impaired retrieval during the remote memory one. These findings confirm that ATN but not ILN/LT lesions disrupt the acquisition of spatial memory and provide new evidence that the ILN/LT region contributes to remote memory processing. Thus, the lateral thalamus may modulate some aspects of remote memory formation and/or retrieval during the course of systems-level consolidation.