  Purpose: Auditory verbal hallucinations (AVHs) are speech perceptions in the
absence of a external stimulation. An influential theoretical account of AVHs
in schizophrenia claims that a deficit in inner speech monitoring would cause
the verbal thoughts of the patient to be perceived as external voices. The
account is based on a predictive control model, in which verbal self-monitoring
is implemented. The aim of this study was to examine lip muscle activity during
AVHs in schizophrenia patients, in order to check whether inner speech
occurred. Methods: Lip muscle activity was recorded during covert AVHs (without
articulation) and rest. Surface electromyography (EMG) was used on eleven
schizophrenia patients. Results: Our results show an increase in EMG activity
in the orbicularis oris inferior muscle, during covert AVHs relative to rest.
This increase is not due to general muscular tension since there was no
increase of muscular activity in the forearm muscle. Conclusion: 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 the
inner speech monitoring dysfunction occurs and how inner speech is controlled
and monitored. This will help better understanding how AVHs occur.
