Relapse of conditioned taste aversion in rats exposed to constant and graded extinction treatments

In a generalized bait-shyness preparation of rats, the graded extinction procedure was not effective in preventing the relapse of conditioned aversion to a target taste. The present study is a replication of this finding in a conventional taste aversion preparation using a sodium chloride (NaCl) solution as the conditioned stimulus (CS) and an injection of poisonous lithium chloride (LiCl) as the unconditioned stimulus (US). After aversive conditioning of salty taste by a CS-US pairing, its extinction was administered by two different experimental procedures. The rats in the constant extinction group were repeatedly exposed to the target CS (NaCl solution). For the rats in the graded extinction group, the concentration of NaCl was gradually increased from a low level to the original one, and an additional interfering sweet taste was gradually faded out. The rats in the graded extinction group were equally or more prone to relapse than those in the constant extinction group. This result was observed by the second reacquisition treatment (Experiment 1), spontaneous recovery after a 30-day interval (Experiment 2), and renewal upon return to the acquisition context (Experiment 3). These results extended the generality of our previous finding, and its theoretical and clinical implications are discussed.