Abnormal oculomotor corollary discharge signaling as a trans-diagnostic mechanism of psychosis

Corollary discharge signals (CD) are “copies” of motor signals sent to sensory areas to predict the corresponding input. Because they are used to distinguish actions generated by oneself versus external forces, altered CDs are a hypothesized mechanism for agency disturbances in psychosis (e.g., delusion of alien control). We focused on the visuomotor system because the CD relaying circuit has been identified in primates, and the CD influence on visual perception can be quantified using psychophysical paradigms. Previous studies have shown a decreased influence of CD on visual perception in (especially more symptomatic) individuals with schizophrenia. We therefore hypothesized that altered CDs may be a trans-diagnostic mechanism of psychosis. We examined oculomotor CDs (using the trans-saccadic localization task) in 49 participants with schizophrenia or schizoaffective disorder (SZ), 36 psychotic bipolar participants (BPP), and 40 healthy controls (HC). Participants made a saccade to a visual target. Upon saccade initiation, the target disappeared and reappeared at a horizontally displaced position. Participants indicated the direction of displacement. With intact CDs, participants can remap the pre-saccadic target and make accurate perceptual judgements. Otherwise, participants may use saccade landing site as a proxy of pre-saccadic target. We found that both SZ and BPP were less sensitive to target displacement than HC. Regardless of diagnosis, patients with more severe positive symptoms were more likely to rely on saccade landing site. These results suggest a reduced influence of CDs on visual perception in SZ and BPP and, thus, that altered CD may be a trans-diagnostic mechanism of psychosis.