Abstract
Pairing of a gustatory CS and the visceral US induced by lithium chloride (LiCl) results in reduction of consumption of CS solution. This reduction is termed conditioned taste aversion (CTA). Pre-exposure to CS alone prior to the conditioning disrupts the conditioning (latent inhibition) and so is pre-exposure to US. The US pre-exposure effect is hypothesized to be due to tolerance, habituation, or the associative blocking effect. We studied the dose effect of US pre-exposure on CTA. In 3 experiments, rats were exposed to 10 doses of LiCl before the CTA procedure that consisted of ingesting a saccharin solution (0.1%) followed by injection of a constant dose of LiCl (7.632mg/rat). If the pre-exposure reduced the associability of the US, the CTA should be less. Exp. 1: Pre-exposure to 4 or 8 ml/kg of 0.15M LiCl, 1, 2 or 4 days prior to CTA did not have effect. Exp. 2: Pre-exposure to 0.5, 1, 2, 16, 32 ml/kg 1-day prior disrupted CTA. Exp. 3: Pre-exposure to 1, 16, 20, 32, 40 ml/kg 2-days prior disrupted CTA. Summary: (a) The pre-exposure effect was the same whether the pre-exposure occurred 1 or 2 days prior to conditioning. (b) A clear dose-effect relationship existed. (c) The relation was not monotonic. (d) The lowest preexposure dose, 0.5ml/kg of 0.15M LiCl, not strong enough to induce CTA by itself, was effective. (e) Upon repeated pairing of CS and US, CTA became more pronounced. The results do not support the hypotheses mentioned earlier.
Highlights
The formation of association between two events renders the preceding event the predictive power and the animals’ likelihood of avoiding aversive stimuli and obtaining the objects that sustain life and the species is increased
In Exp.1, a 2×3×3 mixed analysis of variance (ANOVA) indicated (a) no difference between doses of 4 and 8 ml/kg LiCl ( F(1,18)=0.04 ), (b) no difference between the number of days elapsed between the US pre-exposure and conditioning ( F(2,18=2.73, p>.05) ), (c) significant difference between 3 conditioning trials ( F(2,36)=45.09, P< .01 ), and (d) no interaction effects
In a study using a wide range of doses we found some important effect of US pre-exposure: (a) Pre-exposure to LiCl is effective in diminishing the ability of LiCl to induce conditioned taste aversion (CTA). (b) The pre-exposure effect occurred even at a low dose of 0.5ml/kg of 0.15M LiCl, that is not effective by itself to induce a CTA [32]. (c) The dose-effect relation is overall positive, as the dose increases the effect increases; there seems to be at some intermediate doses the efficacy diminishes, the relationship appears to be not monotonic. (d) Upon repeated pairing of CS and US, the CTA effect steadily increased
Summary
The formation of association between two events renders the preceding event the predictive power and the animals’ likelihood of avoiding aversive stimuli and obtaining the objects that sustain life and the species is increased. Contiguity and contingency are conditions essential for two or more events to become associated. The former denotes the proximity in space and time between two events, while the later denotes the likelihood of occurrence of one event when the other has occurred. The two conditions, while necessary, do not guarantee an association to form, . Animals’ previous experience with the event influences the formation. This research is about the effect of pre-exposure to one of the events, the one to be predicted, and the change in its associability
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