Acute tryptophan depletion in healthy subjects increases preferences for negative reciprocity

• Published in: PloS one Vol. 16; no. 3; p. e0249339
• Main Authors: Bengart, Paul, Gruendler, Theo, Vogt, Bodo
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 30.03.2021; Public Library of Science (PLoS)
• Subjects: Addictive behaviors; Adult; Affect - physiology; Amino acids; Behavior; Biology and Life Sciences; Choice Behavior - physiology; Decision making; Depletion; Drafting software; Economics; Experiments; Female; Games; Games, Experimental; Healthy Volunteers; Humans; Male; Medical research; Physical Sciences; Psychological aspects; Psychological research; Punishment; Questionnaires; Reciprocity; Rejection rate; Research and Analysis Methods; Serotonin; Serotonin - metabolism; Social Behavior; Social Sciences; Substance abuse treatment; Tryptophan; Tryptophan - metabolism; Young Adult; Germany
• DOI: 10.1371/journal.pone.0249339
• ISSN: 1932-6203

Reciprocity motivates to reward those who are kind (= positive reciprocity) and to punish those who are unkind (= negative reciprocity). The neurotransmitter serotonin (5-HT) modulates human behavior in numerous social situations, such as retaliation in response to perceived unfairness. In a placebo-controlled study, we used acute tryptophan depletion (ATD) to investigate the influence of available serotonin on choice behavior and reciprocity in the Hawk-Dove game. This game illustrates a conflict situation and incorporates two potential strategies: the cooperative Dove strategy and the uncooperative, more aggressive Hawk strategy. After strategic choices, we elicited the subjects’ expectations (= beliefs) regarding the opponent’s choices and controlled for risk preferences and current mood. We defined strategy choices as negative reciprocity when the participants opted for Hawk in response to an expected Hawk. We hypothesized that the ATD-induced reduction of 5-HT availability would increase participants’ preferences for negative reciprocity. Generalized estimating equations reveal no significant main effect of ATD on assessed belief, mood, or risk attitude. But assessment of ATD’s marginal effects over beliefs suggests that ATD significantly increases the tendency for negative reciprocity, whereas positive reciprocity (Dove in response to an expected Dove) is unaffected. We could therefore demonstrate that 5-HT availability mediates (negative) reciprocal behavior in social decision-making.