CONDITIONING OF FEAR AND CONDITIONING OF SAFETY IN RATS

In separate groups of rats forward and backward procedures for classic al defensive conditioning were superimposed on on-going bar pressing f or food. The forward conditioned stimulus elicited suppression of bar presses, indicating acquisition of fear. The backward stimulus paired with identical shock elicited behaviour typical for rats in a conditio n of safety and caused an increase of bar press rate. Enhancement of b ar presses acquired in the course of backward conditioning was stable, immune to influences from unsignalled shocks presented in the same ex perimental context, and resistant to extinction when all shocks were d iscontinued. Properties of the employed variety of the backward condit ioning procedure are discussed. When a brief shock overshadowed the on set of a backward stimulus, the remaining portion of the stimulus beca me a signal of safety.