Single Session and Repeated Anodal Transcranial Direct Current Stimulation over the Right Dorsolateral Prefrontal Cortex Increases Reflective Thinking but Not Working Memory Updating Performance

Background: Anodal transcranial direct current stimulation (tDCS) over the right dorsolateral prefrontal cortex (DLPFC) has shown to have effects on different domains of cognition yet there is a gap in the literature regarding effects on reflective thinking performance. Objective: The current study investigated if single session and repeated anodal tDCS over the right DLPFC induces effects on judgment and decision-making performance and whether these are linked to working memory (updating) performance or cognitive inhibition. Methods: Participants received anodal tDCS over the right DLPFC once (plus sham tDCS in a second session) or twice (24 h apart). In the third group participants received a single session of sham stimulation only. Cognitive characteristic measures were administered pre-stimulation (thinking disposition, impulsivity, cognitive ability). Experimental tasks included two versions of the Cognitive Reflection Test (numeric vs verbal-CRT), a set of incongruent base-rate vignettes, and two working memory tests (Sternberg task and n-back task). Forty-eight participants (mean age = 26.08 +/- 0.54 years; 27 females) were recruited. Results: Single sessions of tDCS were associated with an increase in reflective thinking performance compared to the sham conditions, with stimulation improving scores on incongruent base rate tasks as well as marginally improving numeric CRT scores (compared to sham), but not thinking tasks without a numeric component (verbal-CRT). Repeated anodal stimulation only improved numeric CRT scores. tDCS did not increase working memory (updating) performance. These findings could not be explained by a practice effect or a priori differences in cognitive characteristics or impulsivity across the experimental groups. Conclusion: The current results demonstrate the involvement of the right DLPFC in reflective thinking performance which cannot be explained by working memory (updating) performance or general cognitive characteristics of participants.