Is spatial memory transformed during the consolidation process? Effect of reminding.

Several studies in rats have shown activation of cortical regions and concurrent deactivation of the hippocampus during the retrieval of spatial memory, as the consolidation process progresses. To determine whether during this post-learning period of memory reorganization, spatial memories are transformed from a specific to a more generic representation, in Experiment 1 we compare remote spatial memory measured using a single probe trial versus relearning. Results show that spatial memory can be effectively retrieved using a single probe trial during the 18 days following learning; after this time a retraining procedure is necessary. In Experiment 2 and 3 we tested the effect of a reminder treatment on the retrieval of remote memory. Results indicate that when the reminder was applied after experimental day 18, the treatment did not significantly improve the retrieval of spatial memory during a retention test (Exp. 2); however, if the reminder was applied before day 18, a significant improvement during the retention test was observed (Exp. 3). In order to investigate the extent to which memory becomes more difficult to retrieve as time passes due specifically to a retrieval deficit, in experiment 4 no significant differences, but marginal ones, were detected between an overtrained group and a control group when the retention test took place 30 days after the end of learning. Overall, the present results suggest that as the consolidation process progresses, spatial information becomes more difficult to recover, in part because the original detailed trace has gradually been transformed into a more schematic representation.