Corollary discharge, auditory hallucinations and schizophrenia – a structural network analysis

Introduction Corollary discharges (CDs) are the reason most people cannot tickle themselves. They are the brain's way of distinguishing whether a stimulus is associated with one's own actions or something else. In neural terms, CDs are copies of motor plans that are propagated to sensory cortex where they can be compared with inputs. A range of phenomena associated with schizophrenia from auditory hallucinations to visual processing difficulties to the ability of patients to tickle themselves can be explained as pathologies in CD mechanisms. Auditory hallucinations for example involve patients failing to perceive themselves as the author of their own inner speech. Objectives and aims To test whether schizophrenia is associated with a structural network disruption that could impair CD signals involved in language processing, adolescents with schizophrenia were examined using magnetic resonance imaging and compared to healthy controls. Methods A graph theoretical approach was used to analyse the connectivity in networks centered on: – Broca's area; – Wernicke's area. Connectivity information was acquired using diffusion tensor imaging (DTI). Results Compared to healthy controls, adolescents with schizophrenia displayed a lower average degree of connectivity with the left inferior frontal gyrus (Broca's area). No significant differences were found in the degree of connectivity with the right inferior frontal gyrus and the superior temporal gyrus bilaterally (Wernicke's area). Conclusions The results suggest a link between schizophrenia and impairment to areas where CDs associated with inner speech plausibly originate.