Stress Transiently Affects Pavlovian-to-Instrumental Transfer

Abstract

Stress has a strong impact in the brain, impairing decision-making processes as a result of changes in circuits involving the prefrontal and orbitofrontal cortices and the striatum. Given that these same circuits are key for action control and outcome encoding, we hypothesized that adaptive responses to which these are essential functions, could also be targeted by stress. To test this hypothesis we herein assessed the impact of chronic stress in a Pavlovian-to-instrumental transfer (PIT) paradigm, a model of an adaptive response in which a previously conditioned cue biases an instrumental goal-directed action. Data reveals that rats submitted to chronic unpredictable stress did not display deficits in pavlovian conditioning nor on the learning of the instrumental task, but were impaired in PIT; importantly, after a stress-free period the PIT deficits were no longer observed. These results are relevant to understand how stress biases multiple incentive processes that contribute to instrumental performance.

Keywords: choices; conditioning; pavlovian-to-instrumental transfer; stress.

Figure 1

Pavlovian conditioning. There were no differences between groups, with all animals increasing the number of head entries during conditioned stimulus exposure. ITI – intertrial interval between presentations of conditioned stimuli CS – conditioned stimulus.*p < 0.05.

Figure 2

Instrumental conditioning. Both experimental groups acquired the lever pressing task and were able to correctly distinguish devalued from valued levers.*p < 0.05.

Figure 3

Stress-induced impairment of Pavlovian-to-instrumental transfer is reversible. Stress exposure resulted in an impairment of the association between Pavlovian and instrumental behavior (A), which was no longer observed after a 6-week period without exposure to stressful stimuli (B). Same – conditioned stimulus (sound) predicted the same outcome as the lever pressed; Diff – conditioned stimulus (sound) predicted a different outcome as the lever pressed. *p < 0.05.