EVIDENCE FOR SIMULTANEOUS EXCITATORY AND INHIBITORY ASSOCIATIONS IN THE EXPLICITLY UNPAIRED PROCEDURE

These experiments examined the associative status of a 10-s CS (white noise) which, during Pavlovian conditioning, singly alternated with the US (footshock) in an explicitly unpaired fashion, with either a short (55 s) or with a long (420 s) intertrial interval. Results from conditioned punishment summation tests showed that following 8 sessions of conditioning (7 CSs and 7 USs in each session) the explicitly unpaired CS functioned as a conditioned excitor (Experiments 1-3), relative to the CS-only control, if the intertrial interval was short but not if that interval was long (Experiment 1). The excitatory property of the explicitly unpaired CS was still evident following a lengthy retention interval (28 days) during which rats remained in their home cage (Experiment 3). The explicitly unpaired CS functioned as a conditioned inhibitor if it had undergone extinction, after extinction of the contextual cues of the conditioning context (Experiment 2). Finally, the explicitly unpaired CS was also a conditioned inhibitor after only the contextual cues of the conditioning chamber were extinguished (Experiment 3). This latter finding was taken as evidence that under conditions of limited conditioning and when the CS and US trials are closely spaced, either excitatory CS-context and context-US associations or context-CS and CS-US associations, or all of these, were formed. These associations imbued the CS with enough excitation to not only obscure conditioned inhibition but to make the CS a net excitor. © 1994 Academic Press, Inc.