Improving working memory in schizophrenia: Effects of 1 mA and 2 mA transcranial direct current stimulation to the left DLPFC

Abstract

Deficits in various cognitive processes, such as working memory, are characteristic for schizophrenia, lowering patients' functioning and quality of life. Recent research suggests that transcranial direct stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) may be a potential therapeutic intervention for cognitive deficits in schizophrenia. Here, we examined the effects of online tDCS to the DLPFC on working memory (WM) performance in 40 schizophrenia patients in two separate experiments with a double blind, sham-controlled, cross-over design. Patients underwent single sessions of active and sham tDCS in a randomized order. Stimulation parameters were anode F3, cathode right deltoid muscle, 21 min tDCS duration, 1 mA tDCS in Experiment 1 (N = 20) and 2 mA tDCS in Experiment 2 (N = 20). Primary outcome was the change in WM performance as measured by a verbal n-back paradigm (1- to 3-back). Irrespective of the stimulation intensity, data analysis showed a significant higher WM accuracy during active tDCS than during sham tDCS (p = 0.019), but no main effect of stimulation intensity (p = 0.392). Subsequent separate analyses revealed a significantly improved WM performance only during 1 mA (p = 0.048). TDCS facilitated WM functioning in schizophrenia, with an advantage of 1 mA over 2 mA. Our results support the notion that tDCS may be a potential treatment for cognitive deficits in schizophrenia and emphasize the need for future research on the specific stimulation parameters.