Abstract

The paraventricular nucleus of the thalamus (PVT) has been implicated in cue-induced motivated behaviors. Although reward-associated cues (conditioned stimuli, CSs) contain different types of information including predictive information of future reward delivery and incentive (motivational) value of the reward, it remains unknown whether PVT neurons represent predictive and incentive information of CSs. It is suggested that neural activity just after the onset of CSs (early activity) and that just before reward delivery (late activity) might more strongly represent predictive and incentive information, respectively. In this study, rats were trained to lick a tube, which was protruded close to their mouth just after a CS, to obtain a reward (sucrose or water) (cue-induced licking task). Auditory and visual CSs were used: each elemental cue (CS) predicted reward or non-reward outcome, while simultaneous presentation of the two elemental cues (configural cues) predicted the opposite reward outcome. We recorded PVT neurons in the cue-induced licking task, and report that half of the CS-responsive PVT neurons responded selectively to the CSs predicting reward outcome regardless of physical property of the cues (CS+-selective). In addition, the early activity of the CS+-selective neurons discriminated reward/non-reward association (predictive information) and was less sensitive to reward value and motivation reflected by lick latency (incentive information), while the late activity of the CS+-selective neurons was correlated with reward value and motivation rather than reward/non-reward association. Early and late population activity of the CS+-selective neurons also represented predictive and incentive information of the CSs, respectively. On the other hand, activity of more than half of the PVT neurons was correlated with individual licking during licking to acquire reward. Taken together, the results suggest that the PVT neurons engage in different neural processes involved in cue-induced motivated behaviors: CS encoding to determine reward availability and form motivation for reward-seeking behavior, and hedonic mouth movements during reward consumption.

Highlights

  • The paraventricular nucleus of the thalamus (PVT) is one of the midline thalamic nuclei

  • The PVT receives inputs from the subcortical areas related to motivation and emotion including the hypothalamus, amygdala, hippocampus, dorsal raphe, etc. (Hsu and Price, 2009; Li and Kirouac, 2012) and inputs from the frontal cortex related to higher cognition including the anterior cingulate, prelimbic, and infralimbic cortices (Li and Kirouac, 2012)

  • The present study investigated the neural representation of this information in the rat PVT by recording PVT neuronal activity in a cue-induced licking task (Oyoshi et al, 1996; Takenouchi et al, 1999; Toyomitsu et al, 2002; Matsuyama et al, 2011)

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Summary

INTRODUCTION

The paraventricular nucleus of the thalamus (PVT) is one of the midline thalamic nuclei. (Nakahara et al, 2004; Hamlin et al, 2009; James et al, 2010; Marchant et al, 2010; Browning et al, 2014; Clark et al, 2017), while activation of the PVT neurons increases instrumental behaviors for sucrose (Labouèbe et al, 2016) These results suggest that the PVT might be involved in the transformation of information of reward-associated cues into reward-seeking motivation. Two previous neurophysiological studies reported differential neuronal responses during performance of a Pavlovian conditioning task or inhibitory responses to reward omission (Li et al, 2016; Do-Monte et al, 2017), consistent with a PVT role in motivated behaviors It remains unknown how these two types of information are represented in the PVT. We show that the activity of some CS-responsive PVT neurons represents predictive and incentive information of rewards regardless of stimulus sensory modality

MATERIALS AND METHODS
A Experimental setup
RESULTS
DISCUSSION
ETHICS STATEMENT
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