An isolated retrieval trial before extinction session does not prevent the return of fear

Several studies have shown that an isolated retrieval trial before the extinction session (retrieval-extinction) prevents the return of fear memory by inhibition of reconsolidation. Other studies have reported that retrieval-extinction did not prevent the return of the fear. To date, it is still unclear whether retrieval-extinction prevents the return of the original fear memory. A previous study revealed that reconsolidation of conditioned fear memory was not induced by the brevity of the retrieval session. Thus, we examined whether the number of retrievals in the retrieval-extinction paradigm was involved in the prevention of return of fear (Experiment 1). Furthermore, studies with different-age experimental subjects have shown conflicting results. We investigated the potential impact of age on the inhibitory effect of retrieval-extinction on the return of fear (Experiment 2). Our major findings were as follows: (1) Retrieval-extinction procedure did not prevent the return of fear, regardless of the intensity (number of presentations) of the stimulus inducing retrieval of fear memory. (2) The mice in both juvenile and adult age groups (4 and 8 weeks old) retrieved fear memory after retrieval-extinction. These results suggest the possibility that extinction after retrieval does not inhibit reconsolidation of previously consolidated fear memory.