Figure 1.

Classical conditioning paradigm and behavioral results after isotonic MnCl₂ injections. A. Schematic of the classical conditioning paradigm. Each trial consisted of the presentation of a visual stimulus on a computer screen followed 2.5 seconds later by the trial outcome. In CS+ trials, the visual stimulus was an orange star, and the outcome was a liquid reward. In CS− trials, the visual stimulus was a blue circle, and the outcome was no reward. Trials were presented in random order. Inter-trial intervals (ITI) were 5 seconds in length. B. Percentages of CS+ (black bars) vs CS− (gray bars) trials with in anticipatory licking. Both monkeys S and T showed significantly more anticipatory licking in CS+ trials, as expected. C. Licking amplitude (changes in voltage measured by a strain gauge) as a function of time in a single behavioral session for monkey S. The left panel shows all of the CS+ trials in this session; the right panel shows all of the CS− trials. The timing of significant increases in amplitude is marked with green stars. Anticipatory licking began more than 1 second before trial outcome in the CS+ trials, but not in most of the CS− trials. Licking also increases after the delivery of the reward in CS+ trials.