International Journal of Comparative Psychology

We explored renewal of formerly acquired and then extinguished fear in rats. After 24 paired trials of a tone and an electric shock, acquired fear to the tone was extinguished in another context by repeated exposure to the tone alone. Conditioned fear was behaviorally extinguished by the 32nd trial of tone exposure; 40 or 80 additional extinction trials (i.e., a total of 72 or 112 extinction trials) were administered to independent groups of rats. Extinguished fear was renewed by testing the tone in the original context, independently of the amount of the preceding extinction training. The finding suggests that this type of fear renewal is difficult to prevent even after extensive extinction training prior to context change. Fear renewal also took place by shifting contexts after 72 extinction trials, when the fear had been extinguished in the context of acquisition. This kind of renewal was, however, prevented by extending extinction training to 112 trials.