Anodal Stimulation of the Left DLPFC Increases IGT Scores and Decreases Delay Discounting Rate in Healthy Males.

Qinghua He,Tingyong Feng,Chuansheng Chen,Gui Xue,Mei Chen,Antoine Bechara

doi:10.3389/fpsyg.2016.01421

Abstract

Previous correlational imaging studies have implicated the dorsolateral prefrontal cortex (DLPFC) in decision making. Using High-Definition Transcranial Direct Current Stimulation (HD-tDCS), the present study directly investigated the causal role of the DLPFC in performing the Iowa Gambling Task (IGT) and the Inter-Temporal Choice (ITC) task. Three experiments were conducted: Experiment 1 (N = 41) to study the left DLPFC, Experiment 2 (N = 49) to study the right DLPFC, and Experiment 3 (N = 20, a subset of those in Experiment 1) to switch the experimental and control conditions. All participants were healthy male college students. For Experiments 1 and 2, participants were randomly assigned to either the HD-tDCS or the sham stimulation condition. For Experiment 3, participants were assigned to the condition they were not in during Experiment 1. Results showed that HD-tDCS over the left DLPFC increased IGT score, decreased the recency parameter in IGT, and lowered delay discounting rate (k) in the ITC task. We discussed the potential roles of impulse control and time perception in mediating the effect of tDCS stimulation of left DLPFC on decision making. Our results have clinical implications for the treatment of disorders involving poor decision-making, such as addictions.

Highlights

Decision making requires a trade-off between gains and losses (Levin et al, 2012)
Using high-definition anodal tDCS stimulation over the left or right dorsolateral prefrontal cortex (DLPFC), we found that stimulation over the left, but not that over the right DLPFC led to higher Iowa Gambling Task (IGT) score, lower recency parameter based on the revised Expectancy Valence Model (rEV) model, and lower delay-discounting rate (k)
The present study investigated the role of DLPFC in decision making as assessed by the IGT and the Inter-Temporal Choice task (ITC) task

Summary

Introduction

Decision making requires a trade-off between gains and losses (Levin et al, 2012). Behavioral economists have argued that good decision making is to maximize our expected utility over the long term (Summerfield and Tsetsos, 2015). The Iowa Gambling Task (IGT) is probably the most commonly used experimental paradigm in clinical settings to assess the ability to sacrifice immediate interests in favor of long-term benefits (Bechara et al, 1994). On this task, participants choose one deck from four and over time normal participants gradually learn to choose from the two advantageous. The other commonly used task, especially among behavioral economists, is the Inter-Temporal Choice task (ITC), on which participants choose between a small immediate reward and a larger later one. Future outcomes are devalued as a function of delay, which is referred to as the delay discounting (Peters and Buchel, 2011) and is well described by a hyperbolic discount function (Kirby and Herrnstein, 1995; Myerson and Green, 1995; Roelofsma, 1996; Rachlin et al, 2000)

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