Potential impact of bifrontal transcranial random noise stimulation (tRNS) on the semantic Stroop effect and its resting-state EEG correlates

Abstract

Objective: The Stroop effect performance reflects cognitive resistance to interference. We aimed to investigate the effect of a single transcranial random noise stimulation session (tRNS) applied over the dorsolateral prefrontal cortex (DLPFC) on the semantic Stroop effect and its resting electroencephalography (EEG) correlates (β/α ratio).

Methods: In a randomized, double-blind study, healthy volunteers were allocated to receive either one session of active tRNS (n=8) or one session of sham tRNS (n=11). The anode pad was placed on the scalp over the right-DLPFC and the cathode pad was placed over the left-DLPFC. A computerized adaptation of the French Stroop Color-Word Test (Victoria version) and a resting-state continuous EEG recording were administered before and after the tRNS.

Results: No significant difference were observed for either Stroop Interference/Congruent (F_(1,15)=0.5, P=.5, BF=.19) or Interference/Cross (F_(1,14)=3.2, P=.1, BF=0.25) ratios. No significant effect of tRNS was observed on EEG β/α ratios across electrodes (F_(5,95)=0.6, P=.7, BF=0.59e^-05). Under active stimulation, Pearson's tests showed significant correlations with moderate evidence between post-pre differences of Stroop Interference/Congruent and Fz-β/α ratios (r=0.88, P=.02, BF=4.05), and Stroop Interference/Crosses and Cz-β/α ratios (r=0.89, P=.008, BF=8.25), while the same correlations did not reach significance under sham conditions.

Discussion: We observed no significant changes in either semantic Stroop task reaction time or its EEG correlates after tRNS. However, we provide the original finding that fronto-central β/α activity becomes related to cognitive resistance to interference when the DLPFC is stimulated with random noise current. The results suggest a potential resynchronization of relevant brain frequency patterns into Stroop-related cortical involvement.

Keywords: Dorsolateral prefrontal cortex; Inhibitory control; Noninvasive brain stimulation; Resting-EEG; Semantic Stroop task; Stroop effect; Transcranial random noise stimulation.