Comparing transcranial direct current stimulation and transcranial random noise stimulation over left dorsolateral prefrontal cortex and left inferior frontal gyrus: Effects on divergent and convergent thinking

Abstract

The essential role of creativity has been highlighted in several human knowledge areas. Regarding the neural underpinnings of creativity, there is evidence about the role of left dorsolateral prefrontal cortex (DLPFC) and left inferior frontal gyrus (IFG) on divergent thinking (DT) and convergent thinking (CT). Transcranial stimulation studies suggest that the left DLPFC is associated with both DT and CT, whereas left IFG is more related to DT. However, none of the previous studies have targeted both hubs simultaneously and compared transcranial direct current stimulation (tDCS) and random noise stimulation (tRNS). Additionally, given the relationship between cognitive flexibility and creativity, we included it in order to check if the improvement in creativity may be mediated by cognitive flexibility. In this double-blind, between-subjects study, 66 healthy participants were randomly assigned to one of three groups (N = 22) that received a transcranial direct current stimulation (tDCS), transcranial random noise stimulation (tRNS), or sham for 20 min. The tDCS group received 1.5 mA with the anode over the left DLPFC and cathode over the left IFG. Locations in tRNS group were the same and they received 1.5 mA of high frequency tRNS (100–500 Hz). Divergent thinking was assessed before (baseline) and during stimulation with unusual uses (UU) and picture completion (PC) subtests from Torrance Creative thinking Test, whereas convergent thinking was evaluated with the remote association test (RAT). Stroop test was included to assess cognitive flexibility. ANCOVA results of performance under stimulation (controlling for baseline performance) showed that there were significant differences in PC (F = 3.35, p = 0.042, np2 = 0.10) but not in UU (F = 0.61, p = 0.546) and RAT (F = 2.65, p = 0.079) scores. Post-hoc analyses showed that tRNS group had significantly higher scores compared to sham (p = 0.004) in PC. More specifically, tRNS showed higher performance in fluency (p = 0.012) and originality (p = 0.021) dimensions of PC compared to sham. Regarding cognitive flexibility, we did not find any significant effect of any of the stimulation groups (F = 0.34, p = 0.711). Therefore, no further mediation analyses were performed. Finally, the group that received tDCS reported more adverse effects than sham group (F = 3.46, p = 0.035). Altogether, these results suggest that tRNS may have some advantages over tDCS in DT.

Effects of online tDCS and hf-tRNS on reading performance in children and adolescents with developmental dyslexia: a study protocol for a within-subject, randomized, double-blind, and sham-controlled trial

“…Previous findings have shown stronger effects of tRNS compared to tDCS on language and learning abilities, including mathematical skills (66), as well as on other cognitive (25,26,34,35) and perceptual processes (37).…”

“…While tES has been increasingly applied in developmental age, there are limited studies that have systematically investigated the safety and tolerability of tES in children and adolescents [ (38,(81)(82)(83); for a review, see (39)], overall promoting tES as a safe method as for adults. Furthermore, while evidence suggests that tRNS is a safe and potentially less perceptible technique compared to tDCS (25,35,36), only one study has directly compared the safety and tolerability of the two techniques in children and adolescents (25), demonstrating that tRNS is less perceptible and potentially preferable in paediatrics.…”

“…Nevertheless, to the best of our knowledge, the direct effects of tRNS on reading in individuals with DD have not been tested. Additionally, although tDCS and tRNS have been compared in populations with and without neurodevelopmental disorders [e.g., ADHD: (25,26); healthy adults: (34,35)], their effects have not been directly compared in individuals with DD. Regarding children and adolescents with ADHD, tRNS has shown to be more effective than tDCS in improving ADHD symptoms, working memory, and processing speed (25,26).…”

“…Regarding children and adolescents with ADHD, tRNS has shown to be more effective than tDCS in improving ADHD symptoms, working memory, and processing speed (25,26). Concerning healthy adults, tRNS has demonstrated better results compared to tDCS in tasks involving working memory and divergent/convergent thinking (34,35).…”

“…Both tDCS and tRNS are considered highly promising tES techniques for the paediatric population due to their favourable safety profile, high tolerability, versatility, ease of use, and low cost (25,(36)(37)(38)(39)(40)(41). Interestingly, concerning safety and feasibility, both neurophysiological and behavioural studies [respectively, (25,35,36)] showed that tRNS has higher skin perception thresholds, lower response rates to adverse events, and more effective blinding, making it a preferable option for the paediatric population.…”