In late October 2025, researchers from UNSW Sydney published a study providing the strongest evidence yet for the long-held theory that auditory hallucinations in schizophrenia result from the brain misinterpreting its own inner speech. Using brainwave analysis, the study showed that the brains of people experiencing hallucinations reacted to their own internal monologue as if it were an external voice. 

How the brain typically processes inner speech

In a healthy brain, a mechanism called “corollary discharge” helps to distinguish internal thoughts from external sounds. 

• When a person thinks to themselves, a corollary discharge signal is sent to the auditory cortex to quiet the “inner voice”.
• This signal informs the brain that the thought is self-generated, so the auditory cortex does not react to it as an outside sound. 

What happens in a schizophrenic brain

The recent EEG study revealed how this process breaks down in people with schizophrenia who hear voices. 

• In those experiencing hallucinations, the normal suppression of the auditory cortex does not occur during inner speech.
• Instead, the brain reacts more strongly to the person’s own internal voice, similar to how it would react to someone else speaking.
• This confusion leads the brain to perceive internal thoughts as external voices, which can feel incredibly real and intrusive. 

Implications of the discovery

• A new biomarker: The brainwave measurement used in the study has the potential to serve as a biomarker for the development of psychosis, enabling earlier detection and intervention.
• Improved treatment: Understanding the biological basis of these hallucinations is a critical step toward developing more effective and targeted treatments beyond traditional talk therapy.
• Reduced stigma: The findings emphasize that auditory hallucinations are not imagined or an indication of “losing touch with reality.” Instead, they are a result of complex changes in how the brain processes and attributes thoughts.