Ventral pallidal encoding of reward-seeking behavior depends on the underlying associative structure.

Jocelyn M Richard,Patricia H Janak,Nakura Stout,Deanna Acs

doi:10.7554/elife.33107

Abstract

Despite its being historically conceptualized as a motor expression site, emerging evidence suggests the ventral pallidum (VP) plays a more active role in integrating information to generate motivation. Here, we investigated whether rat VP cue responses would encode and contribute similarly to the vigor of reward-seeking behaviors trained under Pavlovian versus instrumental contingencies, when these behavioral responses consist of superficially similar locomotor response patterns but may reflect distinct underlying decision-making processes. We find that cue-elicited activity in many VP neurons predicts the latency of instrumental reward seeking, but not of Pavlovian response latency. Further, disruption of VP signaling increases the latency of instrumental but not Pavlovian reward seeking. This suggests that VP encoding of and contributions to response vigor are specific to the ability of incentive cues to invigorate reward-seeking behaviors upon which reward delivery is contingent.

Highlights

The tendency to seek rewards, like many adaptive behaviors, is influenced by multiple dissociable decision-making processes
To assess the degree to which ventral pallidum (VP) encoding of cue-elicited reward seeking depends on the underlying task structure, we trained rats in either an instrumental task or in Pavlovian conditioning
These results suggest that VP neuron firing that predicts and contributes to response latency in the instrumental task is not merely a motor invigoration signal, but more likely a neural instantiation of an underlying decision-making process that is reflected behaviorally by response latency in the instrumental task, but not the Pavlovian task

Summary

Introduction

The tendency to seek rewards, like many adaptive behaviors, is influenced by multiple dissociable decision-making processes. These decision-making processes have different costs and benefits and may be differentially vulnerable to perturbations that contribute to psychopathology. Neurons in the VP are known to respond to a variety of reward-related stimuli, including primary rewards (Itoga et al, 2016; Tindell et al, 2006), Pavlovian cues predicting reward delivery (Smith et al, 2011; Tindell et al, 2005; 2009), cues predicting reward availability (Richard et al, 2016), and cues indicating specific appropriate reward-seeking actions (Ito and Doya, 2009; Tachibana and Hikosaka, 2012). VP responses to cues have been argued to contribute to reward seeking by representing expected reward value (Tachibana and Hikosaka, 2012), but have been suggested to encode

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