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

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=0.5, P=.5, BF=.19) or Interference/Cross (F=3.2, P=.1, BF=0.25) ratios. No significant effect of tRNS was observed on EEG β/α ratios across electrodes (F=0.6, P=.7, BF=0.59e). 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.