The enhancement of cortical excitability over the DLPFC before and during training impairs categorization in the prototype distortion task

► The effects of tDCS and tRNS have been investigated in a categorization task. ► The right and left dorsolateral prefrontal cortex has been targeted. ► Stimulation took place before and during the training part of the task. ► We have observed the prototype effect in the sham stimulation group. ► The prototype-effect was severed in the active stimulation groups. The present study investigated the effects of transcranial weak electrical stimulation techniques applied to the right and left dorsolateral prefrontal cortex (DLPFC) on categorization learning measured using a variant of the prototype distortion task. During the training phase of this task subjects saw low- and high distortions of a prototype dot-pattern. 60 participants received 10min of either anodal or cathodal transcranial direct current (tDCS), transcranial random noise (tRNS) or sham stimulation before and during the training. We have assessed the effects of the intervention during a test phase, where the subjects had to decide whether the consecutive high- and low-distortion versions of the prototype or random patterns that were presented belonged to the category established in the training phase. Our results show that the categorization of prototypes is significantly impaired by the application of anodal tDCS and tRNS to the DLPFC. The prototype-effect, observable in the case of the sham stimulation group, was severed in all active stimulation conditions.