Protective effect of under-reinforcement of passive avoidance against scopolamine-induced amnesia

Administration of antimuscarinic drugs induces amnesia of aversively motivated behaviors. However, when relatively high intensities of footshock are used during training (over-reinforcement), animals become protected against such amnesic state. Moreover, the protective effect is established in a none-or-all fashion, i.e., within a series of increasing intensities a minute augmentation of footshock intensity is sufficient to reach the protective threshold. In the present experiment it was found that very low intensities of aversive stimulation (under-reinforcement), sufficient to produce learning, also protected animals from scopolamine-induced amnesia. These results suggest that acetylcholine is critically involved in memory consolidation of passive avoidance, but only within a limited range of training intensities.