title: Dynamic shaping of dopamine signals during probabilistic Pavlovian conditioning.
abstract: Cue- and reward-evoked phasic dopamine activity during Pavlovian and operant conditioning paradigms is well correlated with reward-prediction errors from formal reinforcement learning models, which feature teaching signals in the form of discrepancies between actual and expected reward outcomes. Additionally, in learning tasks where conditioned cues probabilistically predict rewards, dopamine neurons show sustained cue-evoked responses that are correlated with the variance of reward and are maximal to cues predicting rewards with a probability of 0.5. Therefore, it has been suggested that sustained dopamine activity after cue presentation encodes the uncertainty of impending reward delivery. In the current study we examined the acquisition and maintenance of these neural correlates using fast-scan cyclic voltammetry in rats implanted with carbon fiber electrodes in the nucleus accumbens core during probabilistic Pavlovian conditioning. The advantage of this technique is that we can sample from the same animal and recording location throughout learning with single trial resolution. We report that dopamine release in the nucleus accumbens core contains correlates of both expected value and variance. A quantitative analysis of these signals throughout learning, and during the ongoing updating process after learning in probabilistic conditions, demonstrates that these correlates are dynamically encoded during these phases. Peak CS-evoked responses are correlated with expected value and predominate during early learning while a variance-correlated sustained CS signal develops during the post-asymptotic updating phase.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, Washington 98195.|University of Washington Department of Pharmacology, University of Washington, Seattle, Washington 98195.|Graduate Program in Neurobiology and Behavior, University of Washington, Seattle, Washington 98195.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Hart
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, Washington 98195.|Graduate Program in Neurobiology and Behavior, University of Washington, Seattle, Washington 98195.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Clark
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Washington, Seattle, Washington 98195.|University of Washington Department of Pharmacology, University of Washington, Seattle, Washington 98195.|Graduate Program in Neurobiology and Behavior, University of Washington, Seattle, Washington 98195.
authors.forename: Paul E M
authors.initials: PEM
authors.lastname: Phillips
mesh_terms: D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology*; D003463:Cues; D004298:Dopamine / Q000378:metabolism*; D008297:Male; D009714:Nucleus Accumbens / Q000502:physiology*; D011336:Probability; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012201:Reward
chemical_list: D004298:Dopamine
keywords: Dopamine; Pavlovian; Reinforcement learning; Reward-prediction error; Uncertainty