Enhanced retrieval of unpleasant memory in helpless rats.

Several studies in humans have indicated an association between enhanced retrieval of unpleasant events and depressive mood. No analogy has so far been demonstrated in animals, however. The purpose of the present study was to determine the effect of learned helplessness on the retrieval of unpleasant memory in rats. Animals initially exposed to a single unpleasant event in a passive avoidance task were subjected, respectively, to inescapable, escapable, or no shock stress exposure. A retention test conducted 48 hr following stress exposure showed an enhanced performance for the passive avoidance task in rats subjected to inescapable shock stress. This improved performance was not observed in escapable or no shock stress groups. This finding in the learned helplessness condition in rats, is qualitatively similar to that found in humans in depressive mood.