Disruption in Pavlovian-Instrumental Transfer as a Function of Depression and Anxiety

The Pavlovian-Instrumental Transfer (PIT) paradigm examines probabilistic and reinforcement learning. Disruptions in mechanisms that mediate PIT (i.e., cues not triggering adaptive behaviors) are thought to be contributors to psychopathology, making the study of probabilistic and reinforcement learning clinically relevant. The current study evaluated an appetitive PIT effect and its relationship with symptom dimensions spanning depression and anxiety, with a particular focus on anhedonia. Forty young adults ranging in scores across dimensions of depression and anxiety symptoms completed the PIT paradigm and self-report symptom measures. The PIT paradigm consisted of three phases. The instrumental phase consisted of a contingent association in which participants squeezed a handgrip for monetary reward. The Pavlovian phase established a purely predictive association between three visual stimuli (CS?+?, CS-, baseline) and presence or absence of monetary reward. In the transfer phase, participants’ responses allowed for examination of whether motivational characteristics of Pavlovian predictors influenced the vigor of their handgrip squeezes (instrumental action), which were formerly independent of Pavlovian associations. Analyses revealed a baseline-reward PIT effect, whereby a reward-associated Pavlovian cue enhanced instrumental responding in the transfer phase. However, there were no significant differences between CS?+?and CS- or CS- and baseline cues, suggesting a disrupted interaction of Pavlovian and instrumental learning. Further, the appetitive PIT effect captured in this paradigm was not associated with anhedonia, fears, or general distress. Future work should investigate the influence of mood states using more specific appetitive PIT paradigms to further understanding of the implications of disrupted reflexive and instrumental responding.

     

Differential dependence of Pavlovian incentive motivation and instrumental incentive learning processes on dopamine signaling

Here we attempted to clarify the role of dopamine signaling in reward seeking. In Experiment 1, we assessed the effects of the dopamine D(1)/D(2) receptor antagonist flupenthixol (0.5 mg/kg i.p.) on Pavlovian incentive motivation and found that flupenthixol blocked the ability of a conditioned stimulus to enhance both goal approach and instrumental performance (Pavlovian-to-instrumental transfer). In Experiment 2 we assessed the effects of flupenthixol on reward palatability during post-training noncontingent re-exposure to the sucrose reward in either a control 3-h or novel 23-h food-deprived state. Flupenthixol, although effective in blocking the Pavlovian goal approach, was without effect on palatability or the increase in reward palatability induced by the upshift in motivational state. This noncontingent re-exposure provided an opportunity for instrumental incentive learning, the process by which rats encode the value of a reward for use in updating reward-seeking actions. Flupenthixol administered prior to the instrumental incentive learning opportunity did not affect the increase in subsequent off-drug reward-seeking actions induced by that experience. These data suggest that although dopamine signaling is necessary for Pavlovian incentive motivation, it is not necessary for changes in reward experience, or for the instrumental incentive learning process that translates this experience into the incentive value used to drive reward-seeking actions, and provide further evidence that Pavlovian and instrumental incentive learning processes are dissociable.