Modification of reactivated memory through "counterconditioning".

Four experiments using rats were conducted to determine whether a "counterconditioning" procedure would be effective in altering old, but reactivated, memory. The aversiveness of previously established Pavlovian conditioned stimuli was reduced by giving subjects a highly preferred substance (maltose solution) shortly after a brief exposure to the fear cues (Experiments 1 and 2). No evidence of a time-dependent effect was obtained with a 1-hr. delay between reactivation and maltose (Experiment 2). Groups given noncontingent footshocks in lieu of Pavlovian conditioning (whether or not they subsequently received maltose) showed uniformly little aversion to test cues (Experiment 3). This finding suggests that counterconditioning in this paradigm affects associative memory processes. A time-dependent effect of delayed treatment and other evidence that active memory is necessary for counterconditioning were obtained (Experiment 4). These experiments support the notion that in rats as well as in humans, memory is a malleable process susceptible to postacquisition modifications and revealed the potential value of the reactivation paradigm in studying counterconditioning as a model for desensitization.