Deficit in motor self-monitoring in schizophrenia with passivity experiences : a novel joint position matching paradigm

Deficit in motor self-monitoring is associated with passivity experiences. It is proposed that the loss of the sense of agency in patients with passivity experiences originates from abnormalities in the motor control system. The current study examined the abnormalities of efferent copy and predicted state in the motor control system of patients with relevant (passivity) symptoms. Using a novel paradigm which is a modified joint position matching task, we compared the replication accuracy between voluntary and passive (tactile and verbal) movements in 20 patients with (mean age 31.9 ± 12.0 years) and 20 patients without (mean age 32.3 ± 13.3 years) relevant symptoms and 25 healthy controls (mean age 31.3 ± 8.4 years). It was hypothesized that the replication accuracy is improved in voluntary condition in healthy control and less apparent in patients without relevant symptoms but not be observed in patients with relevant symptoms. The healthy controls and patients without relevant symptoms had better performance in voluntary conditions when compared with passive tactile (2.21 ± 0.75 cm vs 1.79 ± 0.51 cm; p= .02) and both passive conditions (1.95 ± 0.69 cm vs. tactile 1.18 ± 0.51 cm; p< .001 and verbal 1.53 ± 0.57; p=.01) respectively. However, the patients with relevant symptoms had poorer performance in voluntary condition than passive tactile condition (2.26 ± 0.88 vs. 1.86 ± 0.99 cm, p=.03). The findings suggested that schizophrenic patients with passivity experiences are impaired in the motor performances that utilized the direct information from efferent copy and predicted state.