Effects of prefrontal tDCS on working memory performance in chronic alcohol and tobacco use

Abstract Deficits in working memory (WM) are observable in a wide range of those psychiatric disorders associated with decreased activation of the prefrontal cortex. Given that WM is a crucial process supporting various cognitive functions, deficits interfere with daily life tasks and psychiatric treatment. The present study examines the influence of prefrontal brain stimulation on WM performance in alcohol-dependent patients (AD), tobacco users (TU) and healthy controls (HC). In a double-blind, sham-controlled study, transcranial direct current stimulation (tDCS) was applied to upregulate right dorsolateral prefrontal cortex (DLPFC) activity. Participants received anodal tDCS with current at an intensity of 1.5 mA for 20 minutes in the active group. A large reference electrode (10x10cm) was chosen to minimize stimulation effects and situated over the bilateral supraorbital area. While being stimulated, participants performed the n-back task as a measure of WM performance. Results revealed no significant differences in WM performance between active and sham stimulated participants. Further, performance in the AD group did not differ from TU and HC. According to previous research, stimulation the left DLPFC may more effective in enhancing WM performance. Our findings suggest that the use of larger reference electrodes can minimize the impact on underlying brain regions.