12.3 SENSE OF OWNERSHIP AND SENSE OF AGENCY IN SCHIZOPHRENIA PATIENTS

Abstract

Background: Without thinking we accept that we possess a body with which we act upon the world. The feeling of mineness that we perceive toward our body parts, our thoughts and our feelings is referred to as sense of ownership (SoO), whereas sense of agency (SoA) refers to the experience of being the agent of own action and subsequent outcomes. Patients with schizophrenia may complain about the feeling they are not the subject of their own movements. Sometimes such experiences are explained by disturbances in the sense of body ownership. Others explain this feeling as a disturbance in the experience of self-agency. In a first attempt to understand the association between SoA and SoO, we investigated sense of body ownership and self-agency experiences in patients with schizophrenia. Methods: With a Rubber Hand Illusion paradigm, body ownership was assessed in 54 patients with schizophrenia and 56 age and gender matched controls. In this paradigm, a visible rubber hand and the invisible real hand were stroked either synchronously or asynchronously. Subsequently, proprioceptive drift and subjective RHI were measured. With the Action- Inference task, goal-based and prime-based self-agency inferences were assessed in 36 patients and 36 controls. In this task participants believed they were in control of a rotating square that traversed along a path. Participants indicated after each trial to what extent they felt they caused the square to stop at a specific location (i.e., experienced self-agency). Results: Both groups showed the rubber hand illusion, i.e., a stronger proprioceptive drift and higher subjective ratings of the RHI after synchronous compared with asynchronous stroking (all p<0.001). The effect of synchronicity on subjective RHI was significantly stronger in patients with schizophrenia as compared with healthy individuals (p=0.03). In patients the subjective RHI was related to severity of delusions (rho=0.36). A significant effect of goals and primes on agency inferences was found in both groups (p's<0.001). Compared with healthy controls, patients were less informed by primes when inferring self-agency (p=0.02). Conclusions: This study confirms alterations in SoO and SoA in patients with schizophrenia. Group differences were particularly found in multisensory integration processes related to the embodiment (not proprioceptive drift) and in prime-based (not goal-based) agency-inferences. A possible explanation might come from the distinction between bottom-up (i.e., sensory/ motor input) and top-down mechanisms (i.e., cognitive representation of body schema, belief, learned knowledge) that influence SoA and SoO, that is, altered cognitive representations may influence embodiment and implicit agency-inference processing, but not proprioceptive drift and goalbased agency inferencing.