An EMG study of the lip muscles during covert auditory verbal hallucinations in schizophrenia

Auditory verbal hallucinations (AVHs) are speech perceptions in the absence of external stimulation. According to an influential theoretical account of AVHs in schizophrenia, a deficit in inner-speech monitoring may cause the patients' verbal thoughts to be perceived as external voices. The account is based on a predictive control model, in which individuals implement verbal self-monitoring. The authors examined lip muscle activity during AVHs in patients with schizophrenia to check whether inner speech occurred.

Lip muscle activity was recorded during covert AVHs (without articulation) and rest. Surface electromyography (EMG) was used on 11 patients with schizophrenia.

Results showed an increase in EMG activity in the orbicularis oris inferior muscle during covert AVHs relative to rest. This increase was not due to general muscular tension because there was no increase of muscular activity in the forearm muscle.

This evidence that AVHs might be self-generated inner speech is discussed in the framework of a predictive control model. Further work is needed to better describe how inner speech is controlled and monitored and the nature of inner-speech-monitoring-dysfunction. This will lead to a better understanding of how AVHs occur.