Overshadowing and latent inhibition of context aversion conditioning in the rat.

A review is presented of experimental studies, using rats as the subjects, that were designed to establish an animal model of the clinical phenomenon of anticipatory nausea. Experiments 1 and 2 demonstrated that pairing a distinctive context with an illness-inducing injection of lithium chloride endowed the context with new properties, consistent with the proposal that classical conditioning had established an association between the context as the conditioned stimulus and nausea as the unconditioned stimulus. The conditioned response to the context constitutes a form of anticipatory nausea. Experiment 3 examined overshadowing, showing that the presence of a novel salient cue (a flavour) during context conditioning reduced the magnitude of the aversion conditioned to the context. Experiments 4-7 examined the effects of giving exposure to the context prior to conditioning. They demonstrated a latent inhibition effect, that is, a reduction in the magnitude of the aversion in pre-exposed animals. It is suggested that these ways of modulating conditioned aversions could form the basis of interventions for use in the chemotherapy clinic. Anticipatory nausea is assumed to be a consequence of the formation of an association between the cues that constitute the clinic and the drug-induced nausea experienced in their presence. By restricting the development of this association, latent inhibition and overshadowing procedures should be effective in alleviating the problem of anticipatory nausea.