Corollary Discharge Dysfunction and Inner Speech in Schizophrenia (Schizophrenia Bulletin, Oct 2025)

Understanding Voices from Within

Auditory verbal hallucinations (AVH)—hearing voices without external sound—are among the most defining yet puzzling symptoms of schizophrenia. This open-access study by Whitford et al. (2025) explores a long-standing theory: that such voices arise when the brain mistakes inner speech for external sound. Normally, a “corollary discharge” mechanism tells the brain, “This sound came from me.” If that signal fails, self-generated thoughts may be experienced as alien voices.

Testing the Inner Speech Circuit

Using EEG, the researchers compared 55 schizophrenia-spectrum patients with current hallucinations, 44 without, and 43 healthy controls. Participants silently imagined syllables (“ba” or “bi”) while hearing matching or mismatched recorded syllables. In healthy participants, brain responses (N1 component) were suppressed when inner and outer sounds matched—evidence that the brain anticipated the self-generated input. In contrast, hallucinating patients showed the opposite: enhanced N1 signals, as though their inner speech amplified auditory salience instead of dampening it. Patients without current hallucinations showed an intermediate pattern. The stronger the hallucination severity, the greater the reversal of this suppression effect.

Why It Matters

This study provides compelling evidence that auditory hallucinations are linked to a breakdown in the brain’s internal prediction system—the “inner voice filter.” Rather than muting self-generated speech, the schizophrenic brain may heighten its impact, blurring the boundary between self and world. These results suggest that “inner speech–induced suppression” could serve as a biomarker for psychosis risk and point to new interventions focused on restoring sensory prediction and self-monitoring circuits. By bridging neurophysiology and subjective experience, the work helps explain why what should feel like thought can instead sound like someone else’s voice.

Schizophrenia Bulletin, sbaf167, https://doi.org/10.1093/schbul/sbaf167