Effects of Hd-tdcs to the Rsts on Symptoms and Neurophysiology in People with Hallucinations

Introduction: The right superior temporal sulcus (rSTS) is a causal node in the brain network underlying multisensory hallucination production, identified using causal lesion network mapping (1). It is also associated with other multisensory functions like audiovisual integration (AVI; 2). We sought to reduce rSTS activity with cathodal, high-definition transcranial direct current stimulation (HD-tDCS) to reduce hallucinations and enhance audiovisual integration in people with psychotic disorders.

Methods: This pilot study used a double-blind, randomized, sham-controlled design. HD-tDCS was applied to the rSTS using a ring montage with a cathode center and 3 anode surrounds. Stimulation was administered to 12 individuals (6 active stimulation, 6 sham) for 5 days with 2 20-minute sessions per day. Clinical and neurophysiological variables were evaluated at baseline, 5-day follow-up, and 1-month follow-up. Neurophysiology was measured with electroencephalography (EEG) and included activity at rest and during an AVI task. The AVI task was a novel paradigm that paired auditory and visual steady state stimuli to evoke intermodulation frequencies in the steady-state response (SSR; 3–6). Changes were tested with nonparametric tests with an alpha value of .10.

Results: In the active group, clinical measures demonstrated acute significant symptom reductions at the 5-day timepoint (clinician-measured: p=.06, self-reported: p=.06). Measures with significant reductions primarily indexed general illness severity. Data from active hallucinators (3 per group) indicated a trend of reduced hallucination severity at 5-days in the active group. Clinical measures did not significantly change in sham. EEG measures indicated attenuated alpha power over the rSTS (p=.06) and enhanced auditory SSR (p=.06) in the active group, but not sham, at the 1-month timepoint, suggesting longer-term neuroplastic changes.

Conclusion: HD-tDCS of the rSTS appears to have an acute effect on symptoms of psychotic illness, consistent with our previous case study of this therapy in a person with severe, treatment-resistant hallucinations (7). Symptom changes were mostly indicative of an overall reduction in illness severity, but there was some evidence for alleviation of hallucinations. The stimulation also appears to have had a longer-term effect on neurophysiology, reducing resting state EEG over the stimulated region and enhancing the auditory response. However, we did not note a change in AVI-related frequencies. We will further investigate AVI in this sample by examining other EEG metrics of evoked activity. Given the small size of this pilot study, these results provide preliminary proof-of-concept evidence supporting the initiation of a larger trial in people with hallucinations.