Some 25%–30% of patients with schizophrenia have auditory verbal hallucinations that are refractory to antipsychotic drugs. Outcomes in studies of repetitive transcranial magnetic stimulation suggest the possibility that application of transcranial direct-current stimulation (tDCS) with inhibitory stimulation over the left temporo-parietal cortex and excitatory stimulation over the left dorsolateral prefrontal cortex could affect hallucinations and negative symptoms, respectively. The authors investigated the efficacy of tDCS in reducing the severity of auditory verbal hallucinations as well as negative symptoms.
Thirty patients with schizophrenia and medication-refractory auditory verbal hallucinations were randomly allocated to receive 20 minutes of active 2-mA tDCS or sham stimulation twice a day on 5 consecutive weekdays. The anode was placed over the left dorsolateral prefrontal cortex and the cathode over the left temporo-parietal cortex.
Auditory verbal hallucinations were robustly reduced by tDCS relative to sham stimulation, with a mean diminution of 31% (SD=14; d=1.58, 95% CI=0.76–2.40). The beneficial effect on hallucinations lasted for up to 3 months. The authors also observed an amelioration with tDCS of other symptoms as measured by the Positive and Negative Syndrome Scale (d=0.98, 95% CI=0.22–1.73), especially for the negative and positive dimensions. No effect was observed on the dimensions of disorganization or grandiosity/excitement.
Although this study is limited by the small sample size, the results show promise for treating refractory auditory verbal hallucinations and other selected manifestations of schizophrenia.