Clinical and electrophysiological effects of cathodal HD-tDCS to the right STS in psychosis spectrum disorders: A pilot proof of concept study

The right superior temporal sulcus (rSTS) plays a causal role in multisensory hallucinations, is associated with audiovisual integration (AVI), and displays abnormal activity in psychotic disorders. We sought to reduce psychosis symptoms including hallucinations while modulating AVI and rSTS activity with cathodal, high-definition transcranial direct current stimulation (HD-tDCS) of the rSTS. This double-blind, randomized, sham-controlled pilot study applied HD-tDCS to the rSTS using a ring montage (-1.5 mA cathode center and three .5 mA anode surrounds). Stimulation was administered (N=6 active, N=6 sham) for 5 days with 2 20-minute sessions per day. Assessments occurred at baseline, 5-day, and 1-month timepoints. Electroencephalography (EEG) was recorded during resting state and an AVI steady state (SSR) paradigm. Given the pilot nature of this study, analyses used an alpha threshold of .10. The active group demonstrated reduced clinician-assessed symptoms at 5-days and 1-month, attenuated AVI at 5-days, enhanced auditory SSR and attenuated alpha power over the rSTS at 1-month, and reduced self-reported symptoms at 5-days. Symptom changes correlated with alpha changes. Biological motion, functioning, mood, and cognition did not significantly change. Findings suggest therapeutic effects and successful target engagement. Results provide preliminary proof-of-concept evidence supporting the initiation of a larger trial in psychotic disorders.