Toxicosis affects instrumental behaviour in rats

Three experiments examined the effect of toxicosis on instrumental responding. These studies were prompted by Morrison and Collyer's (1974, Experiment 1) finding that the induction of toxicosis after an instrumental conditioning session produces greater response suppression if the response is reinforced by a novel saccharin solution rather than familiar water during conditioning. Experiments 1 and 2 investigated whether this suppression was mediated by the Pavlovian contingency between the contextual cues and the saccharin solution or the instrumental relationship between the response and the reward. A role for the instrumental contingency was indicated by the greater suppression of the response producing novel saccharin rather than water when the context of both responses was equally associated with the saccharin and illness. Experiment 3 found that extinction of the aversion to a novel reinforcer following aversive conditioning would re-establish an action previously associated with that reinforcer, in contrast to an action whose reinforcer remained aversive. This result was a further indication that the instrumental contingency between the response and reward contributes to response suppression.