The effect of high-frequency rTMS of the left dorsolateral prefrontal cortex on the resolution of response, semantic and task conflict in the colour-word Stroop task

Benjamin A Parris,Nabil Hasshim,Maria Augustinova,Ludovic Ferrand,Gizem Arabaci,Michael G Wadsley

doi:10.1007/s00429-021-02237-4

Abstract

Previous work investigating the effect of rTMS of left Dorso-Lateral Prefrontal Cortex (DLPFC) on Stroop task performance reports no changes to the Stroop effect but reduced reaction times on both congruent and incongruent trials relative to sham stimulation; an effect attributed to an enhanced attentional (or task) set for colour classification. The present study tested this account by investigating whether, relative to vertex stimulation, rTMS of the left DLPFC modifies task conflict, a form of conflict that arises when task sets for colour classification and word reading compete, given that this particular type of conflict would be reduced by an enhanced task set for colour classification. Furthermore, the present study included measures of other forms of conflict present in the Stroop task (response and semantic conflict), the potential effects on which would have been hidden in previous studies employing only incongruent and congruent stimuli. Our data showed that left DLPFC stimulation had no effect on the magnitude of task conflict, nor did it affect response, semantic or overall conflict (where the null is supported by sensitive Bayes Factors in most cases). However, consistent with previous research left DLPFC stimulation had the general effect of reducing reaction times. We, therefore, show for the first time that relative to real vertex stimulation left DLPFC stimulation does not modify Stroop interference. Alternative accounts of the role of the left DLPFC in Stroop task performance in which it either modifies response thresholds or facilitates responding by keeping the correct response keys active in working memory are discussed.

Highlights

Since its inception (Stroop 1935), the Stroop task has become an important clinical tool and has been referred to as the gold-standard measure of selective attention (MacLeod 1992)
Whilst the role of both regions is a matter of ongoing debate, here we focus on the role of the left Dorso-Lateral Prefrontal Cortex (DLPFC)
Our analysis revealed that reaction times (RTs) on incongruent trials were not significantly reduced after DLPFC stimulation

Summary

Introduction

Since its inception (Stroop 1935), the Stroop task has become an important clinical tool and has been referred to as the gold-standard measure of selective attention (MacLeod 1992). Abundant research suggests that interference in the Stroop task is potentially underpinned by conflict at various points in the processing stream including at the level of task set activation, semantic activation and response output (Klein 1964; Monsell et al 2001; see Parris et al (under review)) In this view, task conflict derives from the simultaneous preparation of two task sets (word reading vs colour naming; Goldfarb and Henik 2007; Parris 2014) which creates conflict even before the identity of the Stroop stimulus has been revealed (Hershman and Henik 2019).

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