Retrograde amnesia for previously acquired Pavlovian conditioning: UCS exposure as a reactivation treatment

Abstract

Relatively little information is available on the stimulus conditions that can make old memory vulnerable to amnesic treatment. Three experiments employing a Pavlovian fear conditioning paradigm examined the effectiveness of a UCS exposure in reactivating a previously established memory. Reactivation of memory was indicated by increased susceptibility to retrograde amnesia (RA). Experiment 1A established that a noncontingent footshock (NCFS) 24 h after aversive conditioning, but immediately prior to hypothermia, was effective in reactivating the earlier established memory. This finding was further examined in Experiment 1B, in which it was demonstrated that severity of RA in groups reexposed to the conditioned fear cues, either before or after NCFS, was equivalent to that in subjects given NCFS only prior to hypothermia. Surprisingly, presenting footshock during reexposure to the fear cues (i.e., a brief retraining trial) also permitted induction of RA for old memory. While amnesia was comparable in subjects exposed to hypothermia following one of the four reactivation conditions (NCFS, NCFS/CUE, CUE/NCFS, CUE-FS), differences in memory strength were found among subjects not exposed to hypothermia after their reactivation treatment. Experiment 2 demonstrated that the temporal gradient of amnesia that is characteristic of new learning was also obtained for NCFS-reactivated memory. These findings provide evidence that previously acquired information can be activated by the aversive component of the original training episode, and that this active memory is vulnerable to an amnestic treatment.