Relationship of imprecise corollary discharge in schizophrenia to auditory hallucinations

Context: A forward model of intended thoughts and actions prepares sensory cortex for sensations that are a consequence of those actions. Imprecision of the corollary discharge in schizophrenia may contribute to the misperception of inner experiences and thoughts as voices or auditory hallucinations. Objectives: To assess the precision of the forward model in schizophrenia using the N100 component of the auditory event-related potential to speech that is altered or unaltered, in real time, as it is being spoken. To assess the relationship between auditory hallucinations and the imprecision of the corollary discharge. Design: Prospective case-control study. Setting: Community mental health centers and Palo Alto Veterans Affairs Health Care System, Palo Alto, Calif. Participants: Twenty patients with schizophrenia and 17 sex- and age-matched healthy control subjects. Main Outcome Measures: N100 responses to auditory feedback, which was altered by pitch-shifting the self-voice, substituting an alien voice, or pitch-shifting the alien voice. On each trial, subjects judged whether feedback was self, other, or unsure. Clinical ratings were used to assess severity of auditory hallucinations in patients. Results: In controls, N100 to unaltered self-voice feedback was dampened relative to N100 to altered self-voice or alien auditory feedback. This pattern was not seen in hallucinating patients. This imprecision correlated with the severity of hallucinations and with the percentage of misattribution errors. Conclusion: These data support a connection between auditory verbal hallucinations and the imprecision of the corollary discharge heralding the sensory consequences of thoughts and actions.