Damage to the hippocampus (HPC) causes retrograde amnesia for some memories, but spaced learning mitigates this. Contextual fear conditioning (CFC) studies in rats demonstrate that distributing conditioning over multiple sessions makes a memory less vulnerable to HPC damage, and it has been suggested this occurs through incremental strengthening of the memory outside the HPC via separate bouts of cellular consolidation. To explore this, we examined the number of, and temporal intervals between, spaced CFC sessions required to make a memory less vulnerable to HPC damage. Experiment 1 established six sessions spaced over three days as sufficient to create a memory no longer requiring the HPC. Experiments 2 and 3 found that spacing those six sessions in a single day also created a memory no longer requiring the HPC, but only when the sessions were separated by an interval believed to be sufficient for separate bouts of cellular consolidation to occur.
Author Keywords: consolidation, context fear, hippocampus, memory, retrograde amnesia, spaced learning