Post-extinction Delay Necessary to Induce Retrograde Amnesia for a Moderate Extinction Training Memory

Two experiments using rats were conducted to evaluate the post-extinction delay necessary to obtain retrograde amnesia for a moderate extinction training memory. In Experiment 1, six minutes of extinction (i.e., cue-exposure) was sufficient to reduce fear of the black compartment of a white-black shuttle box, however the amnestic treatment cycloheximide (CHX) failed to produce retrograde amnesia for extinction (i.e., show fear). In Experiment 2, CHX was administered at various post-extinction delays (0-min, 60-min, 75-min, 120-min) to assess whether the active extinction memory could be susceptible to amnesia if the original fear memory had time to reconsolidate. The results indicated that administrating CHX 75 minutes after extinction produced retrograde amnesia for extinction, but not for shorter post-extinction delays, thus demonstrating a temporal gradient. These findings suggest that the extinction memory was active and susceptible to disruption 75 minutes after the extinction session, but the original fear memory may have been protected from the amnestic effects with sufficient time to reconsolidate.

Conditioned Fear in the Fish

Paradise fish, macropodus opercularis, were given inescapable shocks in the black side of a two-compartment box. Following training they showed acquisition of a target-striking instrumental response which permitted them to escape from the black compartment to a white compartment. Non-shocked control Ss also showed evidence of learning, probably based on an exploratory drive, but their behavior was far less persistent than that of the experimental group. The results are compared with those of other studies, on both the fish and mammals, which have investigated the effects of conditioned fear training, and some theoretical implications are drawn.