The effects of prefrontal transcranial direct-current stimulation on semantic control functions

Abstract

Introduction Disrupted control of lexical-semantic processing is a core symptom of several neuropsychiatric disorders and has often been attributed to a compromised function of the prefrontal cortex. Method The goal of the present study was to investigate whether anodal transcranial direct-current stimulation (tDCS) of the left dorsolateral prefrontal cortex (DLPFC) can be used to improve executive control during lexical-semantic retrieval in healthy adults. In a between-subjects design, participants received either prefrontal (N = 40; locations F3 and CP5 of the international 10-10 EEG electrode placement system for anode and cathode, respectively), sham (N = 40), or a control temporoparietal (N = 40; CP6 and CP5 for anode and cathode, respectively) tDCS for 25 minutes with an intensity of 2 mA using 5 × 7 cm rubber electrodes. Before, during, and after (10 min) the tDCS, lexical-semantic functions (initiation, inhibition, and switching) were assessed using word-associative chains (the Associative chain test) and working memory was tested using the Digit backwards task. Results Compared with both the control and the sham stimulation, prefrontal tDCS enhanced semantic inhibition but did not affect semantic initiation or switching. This effect was present during the stimulation and persisted after the stimulation. Working memory capacity was also increased by prefrontal tDCS but was not correlated with the lexical-semantic measures. Conclusion Our findings indicate that tDCS of the left DLPFC can increase semantic inhibition and working memory capacity in healthy adults. This intervention may be potentially useful in the treatment of functionally related neuropsychiatric conditions.