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Updated: Jul 5, 2026
07:47
Measuring Delay Discounting in Humans Using an Adjusting Amount Task
Published on: January 9, 2016
Low-serotonin levels increase delayed reward discounting in humans
Nicolas Schweighofer1, Mathieu Bertin, Kazuhiro Shishida
1Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, California 90089, USA. schweigh@usc.edu
Summary
Low serotonin levels increase impulsivity in humans, leading to a greater preference for immediate rewards over larger delayed ones. This finding aligns with animal studies and suggests serotonin modulates reward discounting.
Area of Science:
- Neuroscience
- Behavioral Economics
Background:
- Serotonin's role in impulsive choice is established in animals.
- Human studies on serotonin and impulsivity have yielded mixed results, focusing on learning speed or choice optimality.
Purpose of the Study:
- To investigate the effect of manipulated central serotonin levels on delayed reward discounting in humans.
- To clarify serotonin's specific role in impulsive choice behavior.
Main Methods:
- Healthy volunteers underwent dietary tryptophan depletion and loading to alter serotonin levels.
- Participants performed a dynamic delayed reward choice task.
- Computational modeling was used to estimate reward choice parameters under varying serotonin conditions.
Main Results:
- Lowered serotonin levels significantly increased the preference for immediate rewards.
- A steeper rate of discounting delayed rewards was observed in the low-serotonin condition.
- No significant differences were found in learning speed or choice variability.
Conclusions:
- Reduced central serotonin levels steepen delayed reward discounting in humans.
- Serotonin may regulate delayed reward discounting through corticobasal ganglia circuits.
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