Hemodynamic retrieval intensity in hippocampus is decreased by pre-exposure to autobiographic test items

The purpose of this experiment was to assess the effects of probe familiarity, the consequences of having recently retrieved an autobiographic memory (AM), on subsequent recall. This was accomplished by replicating an earlier imaging experiment, using the same participants and memory probes. Subtractions between sessions showed significant pre-exposure effects (i.e., drop in BOLD signal intensity) in the prefrontal cortex, thalamus, cerebellum and other brain structures. Further, region of interest (ROI) analysis illustrated a significant decrease in neural activity in the hippocampus in both conditions. The results are discussed in terms of the pre-scan interview technique, a method applied in AM research to procure personal information. Although invaluable, we emphasize it must be used with caution as it can result in a loss of power. The widespread use of this method in AM research may explain why studies often fail to find evidence of significant responding in the hippocampus in response to memory probes. Alternatively, when activity in the hippocampus is reported, it often fails to differentiate between recent and remote memories. This point is of particular importance to the on-going consolidation debate, as it often centers on a failure to detect an effect in the hippocampus in one or both conditions.