Neural Effects of Transcranial Direct Current Stimulation in Schizophrenia: A Case Study using Functional Near-infrared Spectroscopy

A Review of the Effects of Transcranial Direct Current Stimulation for the Treatment of Hallucinations in Patients With Schizophrenia

Some 25% to 30% of patients with schizophrenia report auditory verbal hallucinations (AVHs) that fail to respond adequately to antipsychotic treatments. In such cases, transcranial direct current stimulation (tDCS) has been proposed as a therapeutic option. Here, we aim to provide an exhaustive review of the literature examining the clinical effects of tDCS on AVH in patients with schizophrenia. A systematic search in the PubMed and Web of Science databases yielded 14 results, 7 randomized controlled trials (RCTs) and 7 open-label studies. Among them, 4 RCTs and 7 open-label studies reported a significant reduction of AVH after repeated sessions of tDCS, whereas 3 RCTs did not show any advantage of active tDCS over sham tDCS. Altogether, current studies showed an overall decrease of approximately 26% of AVH after active tDCS and 11% after sham tDCS. One suitable approach to decreasing AVH was to deliver twice-daily sessions of tDCS over 5 consecutive days (10 sessions at 20 minutes each, 2 mA) with the anode over the left dorsolateral prefrontal cortex and the cathode over the left temporoparietal junction. Demographic and clinical parameters such as young age, nonsmoking status, and higher frequencies of AVH occurrence seemed to be predictors of clinical improvement. Further RCTs, with larger sample sizes, are needed to confirm the usefulness of tDCS for AVH.