Abstract
BackgroundThere is increasing evidence that the dorso-lateral prefrontal cortex (DLPFC), a brain region related to reward and motivational processes, is involved in effective response inhibition and that decreased activity in this region coincides with reduced inhibitory capacity. Using transcranial direct current stimulation (tDCS) to manipulate cortical activation, this study examined whether cross-hemispheric tDCS over the DLPFC affected performance on an inhibitory control task.MethodsNeurologically intact participants performed a modified Stroop color-word matching task before and after completing one of two tDCS conditions; (1) anodal stimulation over the left DLPFC or (2) sham tDCS.ResultsThere was a statistically significant effect of tDCS condition on Stroop reaction time (RT) pre-post tDCS change scores. Participants who received anodal stimulation over the left DLPFC demonstrated statistically significant faster RT change scores on the Stroop items compared to participants in the sham condition. Although errors on Stroop incongruent items decreased before and after receiving the tDCS treatment, there were no significant differences in errors on Stroop items between the anodal stimulation over left DLPFC and sham tDCS conditions. Anodal tDCS, which is known to elevate neural excitation, may have enhanced activation levels in the left DLPFC and minimized impairment of inhibitory control, resulting in better task performance.ConclusionsCurrent findings provide preliminary evidence that increased excitation of the left DLPFC improves inhibitory control and are a step toward understanding the potential of tDCS for moderating deficits in inhibitory control.
Highlights
Recent research indicates that inhibitory control, or response inhibition, is a key feature of self-control and may impact upon an individual’s ability to inhibit impulsive responses to stimuli (Friese et al 2008; Hofmann et al 2009; Fujita 2011)
Bonferroni-adjusted paired-samples t-tests revealed statistically significant differences between neutral and incongruent Stroop stimuli words pre-transcranial direct current stimulation (tDCS) for reaction time (RT), t27 = À8.14, P < 0.001, d = 1.11, and error rates, t27 = À4.61, P < 0.001, d = 0.97
These findings are consistent with the Stroop effect in that participants are expected to respond more quickly and accurately on neutral trials compared to incongruent trials
Summary
Recent research indicates that inhibitory control, or response inhibition, is a key feature of self-control and may impact upon an individual’s ability to inhibit impulsive responses to stimuli (Friese et al 2008; Hofmann et al 2009; Fujita 2011). The results indicated that participants in the ‘disinhibition’ group, who had been informed to prioritize response speed, consumed more beer than participants in the ‘restraint’ group who were instructed to prioritise inhibition These findings led Jones et al to suggest that a temporary loss of inhibitory control impacts upon motivated behavior such as alcohol-seeking. Deficits in this brain region, shown to be correlated with reward and motivational processes, appear to be implicated in effective response inhibition and decreased activity in this region coincides with reduced capacity for response inhibition (Heatherton 2011; Hedgcock et al 2012; Friese et al 2013; Hagger and Chatzisarantis 2013) Given this evidence, we propose that increased activity in the DLPFC may enhance inhibitory control and, performance on tasks requiring self-control. We predict that participants will demonstrate better Stroop-task performance, as indicated by faster averaged response latency and decreased error rates, after receiving anodal tDCS over the left DLPFC and controlling for baseline, relative to Stroop performance of participants receiving the sham tDCS
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