In five experiments with rats we examined the aversion established by consumption of a solution of lithium chloride (LiCl). Experiment 1 showed that consumption of LiCl established an aversion to saline (NaCl). Experiment 2 showed that the size of the aversion was reduced in rats given pre-exposure to saline (a latent inhibition effect). Experiment 3 showed that experience of a sucrose-saline compound prior to consumption of LiCl generated an aversion to sucrose (a sensory preconditioning effect). Experiments 4 and 5 examined the effects produced by consumption of a sucrose-LiCl compound and demonstrated reciprocal overshadowing between the two tastes. These results confirm that consumption of LiCl establishes an aversion to the taste of this substance. Their implications for the use of orally consumed LiCl as a technique for the control of predatory behaviour are discussed.Studies of flavour aversion learning have made much use of lithium chloride (LiCl) as the unconditioned stimulus (US), usually in the form of an intraperitoneal injection and usually with the intention of establishing an aversion to some arbitrarily chosen flavour, presented prior to the injection. It has been noted (e.g., Nachman, 1963) that most toxic substances have unpleasant tastes, but that LiCl appears to be one of the exceptions to this rule. Nachman reported that thirsty rats given access to a 0.12 M solution of LiCl drank it readily, at least for the first 5 min of its presentation, during which period they drank about 8 ml. Thereafter the rate of drinking declined, and when tested 3 days later the rats refused to drink LiCl, although they readily drank plain water presented in the same way. Similar results have been reported by Simbayi (1987, Experiments 1 and 4). Nachman suggested that this effect was the consequence of an associative learning process in which the taste of the LiCl had become associated with the aversive consequences (i.e., the nausea) induced by its initial consumption. In support of this conclusion he reported that the rats also refused to drink a sodium chloride (NaCl) solution, which appears (to humans) to have the same (salty) taste as LiCl. Furthermore, Requests for reprints should be sent to G. Hall,

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Experiment 1 established the effectiveness of an appetitive conditioning of odours procedure with snails (Helix aspersa) that was subsequently used for the study of blocking. In this important phenomenon, the conditioning of a CS1 (where CS is the conditioned stimulus) prior to conditioning of a compound, CS1CS2, blocked the conditioning to the CS2. Experiments 2a, 2b, and 2c demonstrated this associative effect using three different experimental controls. Experiments 3a and 3b replicated the blocking effect and allowed us to reject an explanation of blocking based on generalized effects of several treatments of diverse stimuli in blocking and control groups (the pseudoblocking effect). The implications of these results for the study of invertebrate cognition by means of conditioning techniques are discussed.

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