Cathodal tDCS increases stop-signal reaction time.

Transcranial direct current stimulation (tDCS) is a noninvasive method of modulating human brain activity and potentially alters performance in cognitive tasks. Often it is assumed that effects of tDCS modulation depend on the polarity-anodal stimulation typically boost cognitive processes whereas cathodal stimulation hampers them. While most tDCS research focusses on the effects of anodal stimulation, cathodal tDCS effects are underexplored. In the present study, cathodal tDCS over the right dorsolateral prefrontal cortex (rDLPFC) was used to potentially hamper the response inhibition process as measured by the stop-signal task (SST). A 9 cm cathode was always positioned over the rDLPFC while the 35 cm anode was placed over the left deltoid. We contrasted a cathodal stimulation condition (that is assumed to reduce neural processing) with sham stimulation and expected a decrease in SST performance after cathodal tDCS, as evidenced by an increase in stop-signal reaction time (SSRT). In a sample of N = 45 healthy adults, a significant Time × tDCS condition interaction emerged, indicating an increase in SSRT after cathodal tDCS. In a recent study by Friehs and Frings (Journal of Experimental Psychology: Human Perception and Performance, 2018), using a similar study design and stimulation protocol, single-session anodal tDCS over the rDLPFC was used to enhance SST performance as indicated by an acceleration of SSRT. In concert, these results suggest that response inhibition is tied to the neural state of the rDLPFC.