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 (ß/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 ß/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-ß/α ratios (r=0.88, P=.02, BF=4.05), and Stroop Interference/Crosses and Cz-ß/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 ß/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.

Three repeated sessions of transcranial random noise stimulation (tRNS) leads to long-term effects on reaction time in the Go/No Go task.

OBJECTIVE: We aimed to investigate whether the number of sessions delivered within one day influences the acute and long-term effects of transcranial random noise stimulation (tRNS) applied over the dorsolateral prefrontal cortex (DLPFC) on inhibitory control. METHODS: Thirty-six healthy participants were randomly assigned to receive either (i) 3 active (3A), (ii) 1 active and 2 sham (1A2S) or (iii) 3 sham (3S) tRNS sessions. The 3 tRNS were delivered consecutively in the same half-day separated by 30min with the anode over the right and the cathode over the left DLPFC. The effects of tRNS on inhibitory control were assessed 5 times using a Go/No Go task: at baseline (T0), after one tRNS session (T1), after the 3 sessions (T3), 1 (D1) and 8 (D8) days after. RESULTS: As compared to sham, active tRNS did not acutely modulate accuracy in the Go/No Go task but decreased reaction times at Go trials. At D1, participants who received at least one active tRNS sessions (3A and 1A2S groups) were faster than those who received 3 sessions of sham. At D8, only the participants who received 3 active tRNS sessions were faster to successfully respond to Go trials as compared to sham. DISCUSSION: Three active tRNS sessions induced longer effects on reaction times than a single session of active tRNS, compared to sham. These findings suggested that delivering repeated tRNS sessions on the same day induces more sustained effects than delivering a single session.

Prefrontal cortex and impulsivity: Interest of noninvasive brain stimulation.

INTRODUCTION: Impulsivity has been reported in many psychiatric conditions and includes deficits in several cognitive functions such as attention, inhibitory control, risk taking, delay discounting and planning. Many studies have shown that noninvasive brain stimulation (NIBS) techniques modulate the activity of the prefrontal cortex and the functions involved in impulsivity. OBJECTIVE: This article aims to review the literature on the effect of NIBS on impulsivity in healthy subjects aged 18-65 years old, and to highlight research avenues to develop therapeutic alternatives for such disorders. METHOD: We performed a systematic review of the literature in the PubMed database following PRISMA method with "transcranial magnetic stimulation", "repetitive transcranial magnetic stimulation", "transcranial direct current stimulation", "inhibition", "risk", "impulsive behavior", "attention", "reward", "delay discounting", "delay task", "planning", "prefrontal cortex" as key words. RESULTS: We selected fifty-six studies showing modulation of the cognitive functions involved in impulsivity through NIBS. CONCLUSIONS: The data led us to consider new therapeutic alternatives in impulsive disorders by modulating prefrontal cortex activity through NIBS.