Can 40 Hz tACS Quiet Auditory Hallucinations in Schizophrenia?

Why Do Auditory Hallucinations in Schizophrenia Resist Treatment?

Between 60% and 80% of people with schizophrenia hear voices. Antipsychotic medication helps many of them, but up to 30% keep hearing voices despite treatment. For these patients, clinicians have few options left.

A pilot trial published in Translational Psychiatry in January 2025 explored a new approach: tACS for auditory hallucinations. Researchers at Tianjin University and Tianjin Anding Hospital used Starstim 32 to deliver 40 Hz transcranial alternating current stimulation (tACS) alongside patients' usual medication. The study adds to a growing body of Chinese research using Starstim and Enobio, including earlier work on tACS in schizophrenia. The results are early, but they point to a promising direction for brain stimulation research in psychiatry.

What Causes Auditory Hallucinations in Schizophrenia? A Brain Out of Rhythm

Brain regions communicate partly by synchronizing their electrical rhythms, or brainwaves. Gamma oscillations, centred around 40 Hz, help the brain integrate sensory and cognitive information across regions.

In schizophrenia, gamma synchronization is consistently weaker. One well-studied example is the 40 Hz auditory steady-state response (ASSR): when patients listen to clicks repeating 40 times per second, their brains follow the rhythm less strongly than healthy brains do. This response is now studied as an EEG biomarker of the disorder.

One leading explanation for auditory hallucinations links these findings together. The frontal cortex, which generates inner speech, may fail to coordinate with the left temporo-parietal junction, which processes sound. If inner speech is not integrated properly, it may be experienced as a voice. That makes disrupted gamma connectivity a logical target for intervention.

What Is tACS, and Why Use 40 Hz in Schizophrenia?

tACS delivers a weak, sine-wave electrical current through electrodes placed on the scalp. It does not force neurons to fire. Instead, it nudges ongoing brain oscillations toward the stimulation frequency.

When two brain regions are stimulated in phase, at the same frequency and timing, tACS is thought to strengthen the long-range connection between them. That is the rationale behind this trial: stimulate the left prefrontal cortex and left temporo-parietal junction together at 40 Hz, and see whether their communication and the hallucinations improve.

Frequency appears to matter. Earlier trials applying 10 Hz (alpha) tACS to the same regions did not reduce auditory hallucinations. Choosing 40 Hz matches stimulation to the gamma deficit seen in schizophrenia.

How Was the tACS Trial for Auditory Hallucinations Designed?

The study was a double-blind, randomized, sham-controlled pilot trial run at Tianjin Anding Hospital between October 2020 and May 2022. Participants were inpatients with schizophrenia or schizoaffective disorder whose hallucinations had persisted despite at least two different antipsychotics. Of 50 patients recruited, 32 completed every session and were analysed. All continued their medication throughout.

Parameter	Protocol
Device	Starstim 32 (Neuroelectrics)
Frequency	40 Hz
Intensity	1 mA (zero-to-peak) per stimulating electrode
Stimulation sites	AF3 (left dorsolateral prefrontal cortex) and CP5 (left temporo-parietal junction), in phase; return electrode at Cz
Sessions	20 minutes per day, weekdays, for 4 weeks (20 sessions)
Sham condition	3-second ramp-up and ramp-down only, to mimic the skin sensation
Follow-up	2 weeks without stimulation
Outcome measures	PSYRATS hallucination scores; 64-channel EEG during a 40 Hz auditory task, at baseline, week 2, week 4, and week 6

The primary outcome was change in auditory hallucination severity. EEG connectivity was the secondary outcome, used to explore how the stimulation might work.

Does tACS Reduce Auditory Hallucinations in Schizophrenia? Key Results

Patients receiving 40 Hz tACS showed a larger percentage reduction in hallucination severity than the sham group, at week 4 (p = 0.036) and at the 2-week follow-up (p = 0.047). The benefit held after stimulation stopped.

It is worth reading these numbers carefully. Both groups improved over time, since both continued medication. The difference lay in the rate of improvement; absolute hallucination scores did not differ significantly between groups at any single time point.

The EEG findings add a mechanistic layer. At week 4, the tACS group showed stronger gamma-band (30–50 Hz) synchrony centred on the right frontal lobe, including its connections with parietal regions. Network analysis suggested the right frontal lobe began acting more like a hub, able to shift the brain between nearby states with less input.

Interestingly, these changes appeared in the right hemisphere, while the electrodes sat on the left. This points to network-wide effects rather than purely local ones. On safety, no participant reported discomfort during any session.

What Are the Limits of This tACS Schizophrenia Study?

The authors are clear that this is exploratory work, and several limitations shape how the findings should be read:

• Small sample. 32 of 50 recruited patients completed the study, limiting statistical power.

• Modest effect sizes. Group differences appeared in reduction rates, with p-values just under 0.05.

• Blinding not assessed. Participants were not asked which condition they thought they received.

• Possible confounders. Medication, illness duration, and other therapies may have influenced results.

• EEG timing. Recordings took place about an hour after stimulation, and EEG changes were not seen at follow-up.

• No symptom–EEG correlation. The study did not test whether brain changes tracked symptom changes.

  
  

tACS is not an approved treatment for schizophrenia. These results justify larger, well-controlled trials of tACS for auditory hallucinations, which is exactly where the field needs to go next.

What's Next for tACS Research on Schizophrenia and Auditory Hallucinations?

This trial opens several questions about tACS for auditory hallucinations that the next generation of studies can answer:

• Scale. Larger, multisite trials with formal blinding checks.

• Dose. Longer protocols, since the authors suggest four weeks may not be enough for lasting change; intensity is also open, as this trial used 1 mA.

• Frequency specificity. Direct comparisons of gamma and alpha protocols on the same targets.

• Targeting. Montages informed by each patient's own connectivity profile.

• Target engagement. Linking EEG changes to symptom changes within the same patients.

  
  

Answering these questions takes precise, flexible multichannel stimulation, delivered consistently across sessions and sites. That is what Starstim is designed for.

Disclaimer: Starstim 32 is supplied exclusively as an investigational device and is NOT an authorized medical device for routine clinical use.

Planning a tACS study in psychiatry? Talk to our team about protocol design and multichannel montages, or explore Starstim.

Reference

Wang X, Zhang X, Chang Y, Liao J, Liu S, Ming D, et al. Double-blind, randomized, placebo-controlled pilot clinical trial with gamma-band transcranial alternating current stimulation for the treatment of schizophrenia refractory auditory hallucinations. Translational Psychiatry. 2025;15:36. doi:10.1038/s41398-025-03256-z