Neurostimulation techniques are a growing aspect of psychiatric treatment especially as advances in pharmacotherapy have slowed down. Although electroconvulsive therapy (ECT) remains the best studied and perhaps most efficacious form of neurostimulation for treatment-resistant psychosis and mood disorders, it is invasive, requires considerable resources, and remains stigmatized. tDCS by contrast is noninvasive, requires few resources, and has never been portrayed as a form of punishment in novels and films. Although its efficacy for psychosis is yet to be fully established, evidence is accumulating. Because tDCS is relatively easy to administer, controlled experiments with active and sham treatment groups are feasible.
tDCS involves the passage of an electrical current of 1-2 milliamperes across the cerebral cortex by means of 2 electrodes placed on the scalp. To diminish auditory hallucinations, electrodes are placed on the left fronto-temporal region; for negative symptoms, bifrontal placement has been used. The treatment is typically given for 20 minutes twice a day for at least 5 days. Adverse effects are minimal but may include tingling or itching at the site of electrode placement and short-lived somnolence.
According to a review by Mondino, Fecteau and colleagues, 32 studies have examined the effects of tDCS in schizophrenia. Most studies involved patients who were also receiving medication, and several case reports have described safe combination with clozapine. For auditory hallucinations, 14 studies exist including 2 randomized controlled trials (RCTs) which included a total of 54 patients. One RCT found a 30% reduction in treatment-resistant auditory hallucinations after 10 sessions, significantly greater than in the sham-treatment group. The second RCT, however, did not find a significant reduction in auditory hallucinations. The treatment parameters differed between the studies, which confounds interpretation; for instance, in the positive trial, subjects received tDCS twice daily whereas in the negative trial, tDCS was once daily.
In the review, the authors also describe investigations of tDCS on such parameters as functional MRI, auditory and motor evoked potentials, and cognitive measures including executive function. Questions yet to answered include the appropriate duration of each tDCS session, 20 minutes being the most usual; the total duration of treatment, i.e. days or weeks; and the placement of electrodes. The duration of beneficial effect is uncertain, although data to date suggest it may endure for several months, and the role of maintenance treatment requires considerable investigation.
Mondino M, Brunelin J, Palmc U, Brunonid AR, Pouleta E and Fecteau S. Transcranial direct current stimulation for the treatment of refractory symptoms of schizophrenia: current evidence and future directions. Current Pharmaceutical Design. 2015;21:3373-3383. Abstract