T241. Neural Mechanisms of Presence Hallucination and Passivity Experience Induced by Sensorimotor Conflicts in Healthy Subjects: A Robotics-fMRI Study

Background: Deficits in self-monitoring, where comparisons between the sensory outcomes of actions and their predicted consequences are impaired, have been proposed to lead to abnormal bodily experience, hallucinations and psychosis. In line with this theory, recent findings demonstrated that robot-controlled sensorimotor conflicts between upper limb movements and somatosensory feedback on the back are able to induce psychosis-like sensations in healthy subjects. Such states include the presence hallucination (PH), i.e. the sensation that someone is nearby when actually no one is present, and passivity sensations. Methods: We investigated the brain mechanisms underlying these two psychosis-related states in 16 healthy subjects. To this purpose, we relied on an MR-compatible robotic system able to generate the aforementioned sensorimotor conflicts, and thereby inducing PH and passivity experience, while recording resting state and task-related brain activity using fMRI. Results: We initially validated that our robotic system could reliably activate motor and sensory regions, and reproduce the PH and passivity experience. An extended cortical network composed of the bilateral insula and temporo-parietal junction and subcortical areas including the thalamus and the basal ganglia, were more activated in the sensorimotor condition associated with PH. Results from the resting state analysis showed that connectivity between specific somatosensorypremotor regions could predict the strength of PH and passivity sensations, indicating that that disconnections between those areas were associated with higher psychosis-like states. Conclusions: Collectively, these robotically-induced findings shed new light on the neural correlates of mild psychosis sensations in healthy subjects, thereby advancing the scientific understanding of symptomatic hallucinations and psychosis in psychiatry.