Cue-motivated reward seeking is negatively regulated by expected reward magnitude in Pavlovian-instrumental transfer

The Pavlovian-instrumental transfer (PIT) paradigm is widely used to assay the motivational influence of reward-paired cues, which is reflected by their ability to stimulate instrumental reward-seeking behavior. Leading models of incentive learning assume that motivational value is assigned to cues based on the total amount of reward they signal (i.e., their state value). Based on recent findings, we lay out the alternative hypothesis that cue-elicited reward predictions may actually suppress the motivation to seek out new rewards through instrumental behavior in order to facilitate efficient retrieval of a reward that is already expected, before it is lost or stolen. According to this view, cue-motivated reward seeking should be inversely related to the magnitude of an expected reward, since there is more to lose by failing to secure a large reward than a small reward. We investigated the influence of expected reward magnitude on PIT expression. Hungry rats were initially trained to lever press for food pellets before undergoing Pavlovian conditioning, in which two distinct auditory cues signaled food pellet delivery at cue offset. Reward magnitude was varied across cues and groups. While all groups had at least one cue that signaled three food pellets, the alternate cue signaled either one (Group 1/3), three (Group 3/3), or nine food pellets (Group 3/9). PIT testing revealed that the motivational influence of reward-predictive cues on lever pressing varied inversely with expected reward magnitude, with the 1-pellet cue augmenting performance and the 3- and 9-pellet cues suppressing performance, particularly near the expected time of reward delivery. This pattern was mirrored by opposing changes in the food-port entry behavior, which varied positively with expected reward magnitude. We discuss how these findings may relate to cognitive control over cue-motivated behavior.