RT Journal Article
SR Electronic
T1 Low-Serotonin Levels Increase Delayed Reward Discounting in Humans
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 4528
OP 4532
DO 10.1523/JNEUROSCI.4982-07.2008
VO 28
IS 17
A1 Schweighofer, Nicolas
A1 Bertin, Mathieu
A1 Shishida, Kazuhiro
A1 Okamoto, Yasumasa
A1 Tanaka, Saori C.
A1 Yamawaki, Shigeto
A1 Doya, Kenji
YR 2008
UL http://www.jneurosci.org/content/28/17/4528.abstract
AB 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.