Sat, 26 Jul 2008 03:27:53 BST CiteULike: nelmor discounting http://www.citeulike.org/user/nelmor/tag/discounting CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/nelmor/article/2987296 <i>Neuron, Vol. 59, No. 1. (10 July 2008), pp. 161-172.</i><br /><br />Summary Reward from a particular action is seldom immediate, and the influence of such delayed outcome on choice decreases with delay. It has been postulated that when faced with immediate and delayed rewards, decision makers choose the option with maximum temporally discounted value. We examined the preference of monkeys for delayed reward in an intertemporal choice task and the neural basis for real-time computation of temporally discounted values in the dorsolateral prefrontal cortex. During this task, the locations of the targets associated with small or large rewards and their corresponding delays were randomly varied. We found that prefrontal neurons often encoded the temporally discounted value of reward expected from a particular option. Furthermore, activity tended to increase when discounted values for targets were presented in the neuron's preferred direction, suggesting that activity related to temporally discounted values in the prefrontal cortex might determine the animal's behavior during intertemporal choice. Prefrontal Coding of Temporally Discounted Values during Intertemporal Choice Soyoun Kim Jaewon Hwang Daeyeol Lee doi:10.1016/j.neuron.2008.05.010 Neuron, Vol. 59, No. 1. (10 July 2008), pp. 161-172. 2008-07-11T08:28:44-00:00 2008 Neuron 59 1 161 172 decision discounting pfc http://www.citeulike.org/user/nelmor/article/2712965 <i>J. Neurosci., Vol. 28, No. 17. (23 April 2008), pp. 4528-4532.</i><br /><br />Previous animal experiments have shown that serotonin is involved in the control of impulsive choice, as characterized by high preference for small immediate rewards over larger delayed rewards. Previous human studies under serotonin manipulation, however, have been either inconclusive on the effect on impulsivity or have shown an effect in the speed of action-reward learning or the optimality of action choice. Here, we manipulated central serotonergic levels of healthy volunteers by dietary tryptophan depletion and loading. Subjects performed a "dynamic" delayed reward choice task that required a continuous update of the reward value estimates to maximize total gain. By using a computational model of delayed reward choice learning, we estimated the parameters governing the subjects' reward choices in low-, normal, and high-serotonin conditions. We found an increase of proportion in small reward choices, together with an increase in the rate of discounting of delayed rewards in the low-serotonin condition compared with the control and high-serotonin conditions. There were no significant differences between conditions in the speed of learning of the estimated delayed reward values or in the variability of reward choice. Therefore, in line with previous animal experiments, our results show that low-serotonin levels steepen delayed reward discounting in humans. The combined results of our previous and current studies suggest that serotonin may adjust the rate of delayed reward discounting via the modulation of specific loops in parallel corticobasal ganglia circuits. 10.1523/JNEUROSCI.4982-07.2008 Low-Serotonin Levels Increase Delayed Reward Discounting in Humans Nicolas Schweighofer Mathieu Bertin Kazuhiro Shishida Yasumasa Okamoto Saori Tanaka Shigeto Yamawaki Kenji Doya doi:10.1523/JNEUROSCI.4982-07.2008 J. Neurosci., Vol. 28, No. 17. (23 April 2008), pp. 4528-4532. 2008-04-24T13:04:57-00:00 2008 J. Neurosci. 28 17 4528 4532 discounting human reward serotonin http://www.citeulike.org/user/nelmor/article/1916473 <i>Nat Neurosci (4 November 2007)</i><br /><br />Neuroimaging studies of decision-making have generally related neural activity to objective measures (such as reward magnitude, probability or delay), despite choice preferences being subjective. However, economic theories posit that decision-makers behave as though different options have different subjective values. Here we use functional magnetic resonance imaging to show that neural activity in several brain regions-particularly the ventral striatum, medial prefrontal cortex and posterior cingulate cortex-tracks the revealed subjective value of delayed monetary rewards. This similarity provides unambiguous evidence that the subjective value of potential rewards is explicitly represented in the human brain. The neural correlates of subjective value during intertemporal choice. Joseph W Kable Paul W Glimcher doi:10.1038/nn2007 Nat Neurosci (4 November 2007) 2007-11-14T23:00:04-00:00 2007 Nat Neurosci 1097-6256 decision discounting fmri value