EDWARD FISHER, AIMEE STEEN, LINDA LEIJA and Jena Hales
The medial temporal lobes (MTL) are critical for the formation and retrieval of episodic memories, which have both spatial and temporal components. The hippocampus and medial entorhinal cortex, two structures within the MTL, have well characterized spatial processing abilities, with place cells and grid cells, and are both involved in spatial memory (O'Keefe and Dostrovsky, 1971; Hafting et al., 2005; Steffenach, et al. 2005; Hales et al. 2014). The hippocampus has also shown evidence of temporal processing, containing "time cells" (MacDonald, 2011), and is involved in temporal aspects of memory (Fortin, 2002). Unlike the well studied spatial contributions made by the MEC, the temporal functions of this structure are poorly understood. Recent work suggests involvement of the MEC in temporal organization of hippocampal firing patterns, indicating a role for the MEC in hippocampus-dependent temporal processing (Schlesinger et al., 2015). However, the precise role of the MEC in temporal aspects of memory is unclear. In order to examine this question, we developed a temporal object sequence learning task. Rats were presented with a sequence of objects. After a brief delay, rats were given a sequential order probe to test memory for which of two objects was presented earlier in the sequence, followed by an item memory probe to test object recognition memory. Preliminary results from this pilot task contribute to previous data examining temporal memory contributions of the medial entorhinal cortex.