Dissociable Effects of Tryptophan Supplementation on Negative Feedback Sensitivity and Reversal Learning.

Martin Thirkettle,Nazgol Nayeb,Luca Aquili,Thomas Gallagher,Laura-Marie Barker

doi:10.3389/fnbeh.2019.00127

Martin Thirkettle, Nazgol Nayeb + Show 3 more

Open Access

https://doi.org/10.3389/fnbeh.2019.00127

Copy DOI

Abstract

Serotonin has been shown to modulate probabilistic reversal learning (PRL) and negative feedback sensitivity (NFS) in both animal and human studies. Whilst these two measures are tightly coupled, some studies have suggested that these may be mediated by independent mechanisms; the former, representing perseveration and cognitive flexibility, and the latter measuring the ability to maintain a response set (win-stay) at the expense of lose-shift behavior when occasional misleading feedback has been presented. Here, we tested this hypothesis in 44 healthy participants who were administered tryptophan (22 placebo, 22 tryptophan), a precursor to serotonin. We found a dissociable effect of tryptophan supplementation on PRL/NFS. Specifically, tryptophan administration increased NFS compared to the placebo group but had no effect on PRL. We discuss these findings in relation to dosages and with a particular focus on the acute tryptophan depletion (ATD) procedures.

Highlights

Serotonin (5-HT) has long been implicated in probabilistic reversal learning (PRL) and in processing negative feedback
negative feedback sensitivity (NFS) was measured by calculating the probability of switching a response following the presentation of misleading negative feedback, which occurs in a low proportion of trials
To assess the impact of tryptophan administration on NFS, we first took a measurement at baseline

Summary

INTRODUCTION

Serotonin (5-HT) has long been implicated in probabilistic reversal learning (PRL) and in processing negative feedback Both are measured by the PRL task, originally developed in humans (Cools et al, 2002), but adapted in animal studies (Bari et al, 2010; Ineichen et al, 2012). Depressed patients, who are known to have impaired serotonergic function, display normal PRL but higher NFS compared to healthy subjects (Murphy et al, 2003; Taylor Tavares et al, 2008), suggesting that at least behaviorally, these two processes can be decoupled This effect appears to be dose and acute/chronic administration dependent; low (acute: 1 mg/kg) doses of the selective serotonin reuptake inhibitor (SSRI) citalopram in rats impaired PRL and increased NFS, whereas high (acute; 10 mg/kg) doses produced the opposite effect. Numerous studies have looked at tryptophan’s modulation of memory, response to unfairness, emotional processing, attention and executive function (Sobczak et al, 2003; Booij et al, 2006; Murphy et al, 2006; Dougherty et al, 2007; Morgan et al, 2007; Silber and Schmitt, 2010; Cerit et al, 2015; Mohajeri et al, 2015), to the best of our knowledge, this is the first study looking at its effects on PRL and NFS

Participants

Procedure

RESULTS

DISCUSSION

ETHICS STATEMENT