Predictive errors and corollary discharge in schizophrenia

• ¹ San Francisco VA Medical Center, United States
• ² University of California at San Francisco, United States
• ³ University of Melbourne, Australia

Across the animal kingdom, predictions about sensations resulting from motor acts may be instantiated through the corollary discharge mechanism. With each action, an internal comparison is made between corollary discharges of predicted and actual sensations; the closer the match, the greater the suppression of sensation. Schizophrenia may be characterized by dysfunction of this mechanism, altering patients' experience of their thoughts and actions, contributing to hallucinations and perceptual aberrations. Synchronization of neural activity preceding actions may reflect corollary discharge operation. If true, pre-action synchrony will be related to sensory suppression. Further, if corollary discharge deficits are characteristic of schizophrenia, patients will have reduced synchrony and suppression. Sluggish corollary discharge timing may contribute to its dysfunction. In one experiment involving Talking and Playback with 24 patients and 25 controls, phase coherence of single-trial EEG preceding Talking was calculated across trials. Also, suppression of the N1 component of the event-related potential to "ah" onset during Talking compared to Playback was calculated. N1 suppression and pre-speech synchrony were both greater in controls than patients, and in controls, pre-speech synchrony was related to suppression of N1. In another experiment, 21 patients and 25 controls pressed a button to hear their own pre-recorded "ah", with zero or 50ms delays; the 50ms delay normalized N1 suppression in patients. In conclusion, EEG synchrony preceding speech reflects corollary discharge action, dampening auditory responsiveness to self-generated speech. This is deficient in patients. Corollary discharge in patients may travel too slowly to successfully predict sensory experience.