Disrupted auditory N1, theta power and coherence suppression to willed speech in people with schizophrenia

The phenomenon of sensory self-suppression - also known as sensory attenuation - occurs when a person generates a perceptible stimulus (such as a sound) by performing an action (such as speaking). The sensorimotor control system is thought to actively predict and then suppress the vocal sound in the course of speaking, resulting in lowered cortical responsiveness when speaking than when passively listening to an identical sound. It has been hypothesized that auditory hallucinations in schizophrenia result from a reduction in self-suppression due to a disruption of predictive mechanisms required to anticipate and suppress a specific, self-generated sound. It has further been hypothesized that this suppression is evident primarily in theta band activity. Fifty-one people, half of whom had a diagnosis of schizophrenia, were asked to repeatedly utter a single syllable, which was played back to them concurrently over headphones while EEG was continuously recorded. In other conditions, recordings of the same spoken syllables were played back to participants while they passively listened, or were played back with their onsets preceded by a visual cue. All participants experienced these conditions with their voice artificially shifted in pitch and also with their unaltered voice. Suppression was measured using event-related potentials (N1 component), theta phase coherence and power. We found that suppression was generally reduced on all metrics in the patient sample, and when voice alteration was applied. We additionally observed reduced theta coherence and power in the patient sample across all conditions. Visual cueing affected theta coherence only. In aggregate, the results suggest that sensory self-suppression of theta power and coherence is disrupted in schizophrenia.