Corollary Discharge Dysfunction to Inner Speech and its Relationship to Auditory Verbal Hallucinations in Patients with Schizophrenia Spectrum Disorders

BACKGROUND AND HYPOTHESIS: Auditory-verbal hallucinations (AVH)-the experience of hearing voices in the absence of auditory stimulation-are a cardinal psychotic feature of schizophrenia-spectrum disorders. It has long been suggested that some AVH may reflect the misperception of inner speech as external voices due to a failure of corollary-discharge-related mechanisms. We aimed to test this hypothesis with an electrophysiological marker of inner speech. STUDY DESIGN: Participants produced an inner syllable at a precisely specified time, when an audible syllable was concurrently presented. The inner syllable either matched or mismatched the content of the audible syllable. In the passive condition, participants did not produce an inner syllable. We compared the amplitude of the N1, P2, and P3-components of the auditory-evoked potential between: (1) schizophrenia-spectrum patients with current AVH (SZAVH+, n = 55), (2) schizophrenia-spectrum patients without current AVH (SZAVH-, n = 44), (3) healthy controls (HC, n = 43). STUDY RESULTS: The HC group showed reduced N1-amplitude in the Match condition (relative to Passive and Mismatch), replicating our previous results. In contrast, the SZAVH+ group showed the opposite effect: enhanced N1-amplitude in the Match condition (relative to Passive and Mismatch). The SZAVH- group showed reductions in the Mismatch condition (relative to Passive and Match). CONCLUSIONS: This study provides empirical support for the theory that AVH are related to abnormalities in the normative suppressive mechanisms associated with inner speech. This phenomenon of "inner speaking-induced suppression" may have utility as a biomarker for schizophrenia-spectrum disorders generally, and may index a tendency for AVH specifically at more extreme levels of abnormality.