Single session tDCS over the left DLPFC disrupts interference processing.

Whether single session tDCS can impact upon cognition in healthy subjects is currently a heated debate against the background of inconsistent results. In view of the current methodological discussion concerning tDCS we developed an alternative approach to measure effects of single session tDCS on the Stroop task. The left DLPFC was stimulated in a pre-post design using a new electrode set-up (a 9 cm2 electrode was placed over the left DLPFC while a 35 cm2 was placed over the parieto-occipital cortex) contrasting anodal versus cathodal stimulation. The Stroop task was optimized concerning confounding variables that were not controlled in previous attempts to measure the effects of single-session tDCS on the Stroop task. In our sample of N = 32 healthy students we observed a significant single session tDCS effect on the Stroop effect in the error data as in our study cathodal stimulation as compared to anodal stimulation of the left DLPFC disrupted interference processing. This result confirms previous studies suggesting that neuromodulation of the left DLPFC impacts interference processing. Single-session tDCS can impact upon cognitive processes. A rigorous methodical approach is emphasized as the effects seem to be only of small to medium size.

Evaluative priming in a semantic flanker task: ERP evidence for a mutual facilitation explanation.

In semantic flanker tasks, target categorization response times are affected by the semantic compatibility of the flanker and target. With positive and negative category exemplars, we investigated the influence of evaluative congruency (whether flanker and target share evaluative valence) on the flanker effect, using behavioral and electrophysiological measures. We hypothesized a moderation of the flanker effect by evaluative congruency on the basis of the assumption that evaluatively congruent concepts mutually facilitate each other's activation (see Schmitz & Wentura in Journal of Experimental Psychology: Learning, Memory, and Cognition 38:984-1000, 2012). Applying an onset delay of 50 ms for the flanker, we aimed to decrease the facilitative effect of an evaluatively congruent flanker on target encoding and, at the same time, increase the facilitative effect of an evaluatively congruent target on flanker encoding. As a consequence of increased flanker activation in the case of evaluative congruency, we expected a semantically incompatible flanker to interfere with the target categorization to a larger extent (as compared with an evaluatively incongruent pairing). Confirming our hypotheses, the flanker effect significantly depended on evaluative congruency, in both mean response times and N2 mean amplitudes. Thus, the present study provided behavioral and electrophysiological evidence for the mutual facilitation of evaluatively congruent concepts. Implications for the representation of evaluative connotations of semantic concepts are discussed.