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The Journal of Neuroscience, November 19, 2008, 28(47):12294-12304; doi:10.1523/JNEUROSCI.3116-08.2008

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Behavioral/Systems/Cognitive
A Role for Dopamine in Temporal Decision Making and Reward Maximization in Parkinsonism

Ahmed A. Moustafa,^1 * Michael X. Cohen,¹ Scott J. Sherman,² and Michael J. Frank^1 *

¹Department of Psychology and Program in Neuroscience, and ²Department of Neurology, University of Arizona, Tucson, Arizona 85721

Correspondence should be addressed to Michael J. Frank at the above address. Email: mfrank{at}u.arizona.edu

Converging evidence implicates striatal dopamine (DA) in reinforcement learning, such that DA increases enhance "Go learning" to pursue actions with rewarding outcomes, whereas DA decreases enhance "NoGo learning" to avoid non-rewarding actions. Here we test whether these effects apply to the response time domain. We employ a novel paradigm which requires the adjustment of response times to a single response. Reward probability varies as a function of response time, whereas reward magnitude changes in the opposite direction. In the control condition, these factors exactly cancel, such that the expected value across time is constant (CEV). In two other conditions, expected value increases (IEV) or decreases (DEV), such that reward maximization requires either speeding up (Go learning) or slowing down (NoGo learning) relative to the CEV condition. We tested patients with Parkinson's disease (depleted striatal DA levels) on and off dopaminergic medication, compared with age-matched controls. While medicated, patients were better at speeding up in the DEV relative to CEV conditions. Conversely, nonmedicated patients were better at slowing down to maximize reward in the IEV condition. These effects of DA manipulation on cumulative Go/NoGo response time adaptation were captured with our a priori computational model of the basal ganglia, previously applied only to forced-choice tasks. There were also robust trial-to-trial changes in response time, but these single trial adaptations were not affected by disease or medication and are posited to rely on extrastriatal, possibly prefrontal, structures.

Key words: Parkinson's disease; basal ganglia; dopamine; reinforcement learning; computational model; reward

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Received July 4, 2008; revised Sept. 24, 2008; accepted Oct. 7, 2008.

Correspondence should be addressed to Michael J. Frank at the above address. Email: mfrank{at}u.arizona.edu

This article has been cited by other articles:

				N. Bodi, S. Keri, H. Nagy, A. Moustafa, C. E. Myers, N. Daw, G. Dibo, A. Takats, D. Bereczki, and M. A. Gluck Reward-learning and the novelty-seeking personality: a between- and within-subjects study of the effects of dopamine agonists on young Parkinson's patients Brain, September 1, 2009; 132(9): 2385 - 2395. [Abstract] [Full Text] [PDF]

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