Vocal response inhibition is enhanced by anodal tDCS over the right prefrontal cortex

Abstract

Stopping outright (reactive inhibition) and slowing down (proactive inhibition) are types of response inhibition which have mainly been investigated in the manual effector system. This study compared reactive inhibition across manual and vocal effector systems, examined the effects of excitatory anodal transcranial direct current stimulation (anodal tDCS) over the right prefrontal cortex (right-PFC) and looked at the relationship between reactive and proactive inhibition. We hypothesised (1) that vocal reactive inhibition would be less effective than manual reactive inhibition as evidenced by longer stop signal reaction times; (2) that anodal tDCS would enhance both vocal and manual reactive inhibitions and (3) that proactive and reactive inhibitions would be positively related. We tested 14 participants over two sessions (one session with anodal tDCS and one session with sham stimulation) and applied stimulation protocol in the middle of the session, i.e. only during the second of three phases. We used a stop signal task across two stop conditions: relevant and irrelevant stop conditions in which stopping was required or ignored, respectively. We found that reactive inhibition was faster during and immediately after anodal tDCS relative to sham. We also found that greater level of proactive inhibition enhanced reactive inhibition (indexed by shorter stop signal reaction times). These results support the hypothesis that the right-PFC is part of a core network for reactive inhibition and supports previous contention that proactive inhibition is possibly modulated via preactivating the reactive inhibition network.

Effects of High-Definition and Conventional tDCS on Response Inhibition

“…The tDCS parameters used in the present study are consistent with those previously reported in the response inhibition literature to demonstrate increased task performance (i.e. <2 mA stimulation with an anode over the frontal cortex and a stop-signal task to measure response inhibition, [30][31][32][33]. In contrast, to our knowledge there are no published reports demonstrating impaired response inhibition via tDCS, thus supporting our a priori hypothesis.…”

“…Specifically, recent studies have demonstrated improved response inhibition following conventional tDCS with an anode placed over right IFC or presupplemetary motor area (preSMA) and the cathodal electrode placed on the opposite side of the head [30][31][32][33]. Given the well-established role of right IFC and preSMA in response inhibition [2,3], the studies" authors argued that enhanced excitability at the structures underneath the anodal pad drove the observed behavioral improvement.…”

“…HD versus conventional) and stimulation task on response inhibition performance, a series of planned comparisons on the SSRT gain scores (between the tDCS conditions) was performed, despite the lack of a significant interaction in ANOVA results. Comparisons were analyzed via a series of one-tailed t-tests, as prior literature regarding the effects of tDCS on response inhibition uniformly demonstrates a directional effect, with stimulation leading to enhanced SSRT [30][31][32][33].…”

Stimulating stopping? Investigating the effects of tDCS over the inferior frontal gyri and visual cortices

“…Therefore, tDCS can be a powerful tool to make causal inferences about the role of the regions and processes involved in SST performance. Several studies have found decreased SSRTs following anodal stimulation of the IFG [29][30][31][32][33][34] , suggesting that this method can indeed alter inhibition latencies. However, both increased and decreased reaction times in go trials have also been reported 10,31,35 , indicating that anodal IFG stimulation could potentially influence strategic adjustments of task performance rather than an inhibitory process per se.…”

Modulation of inhibitory control by prefrontal anodal tDCS: A crossover double-blind sham-controlled fMRI study

“…In line with these findings, transcranial direct current stimulation (tDCS) studies report that modulations of ventrolateral prefrontal cortex (VLPFC) excitability can improve inhibition performance [ 5 – 12 ]. Jacobson and colleagues [ 7 ] for instance report shorter stop signal reaction times (SSRT) after excitatory anodal than sham tDCS over the rIFG during a stop-signal task (SST; see also [ 10 , 11 ]; and [ 6 , 8 , 12 ] for similar results when applying anodal tDCS over the preSMA).…”