Abstract
Background
Core symptoms of schizophrenia include disturbances in the distinction between the self and the external world. It has been suggested that self-other distinction is governed by predictive processing: Copies of an action’s motor command are used to generate forward models that predict upcoming sensory input. These predictions are compared with actual sensory input, thereby enabling the brain to discard the processing of sensory input arising from one’s own actions. This is reflected in a decreased perception of and reduced BOLD signal for actively versus passively generated sensory input (suppression effect). Here, we investigated whether BOLD suppression effects for the processing of action feedback involving active and passive hand movements differ between patients with schizophrenia and healthy control participants. Since the identity of one’s body also contributes to self-other distinction, we additionally investigated if differences in BOLD suppression effects between patients and healthy controls are further modulated by whether participants see their own or someone else’s hand moving in accordance with their action.
Methods
17 patients with schizophrenia spectrum disorders and 13 healthy controls (matched for age, sex, and educational degree) performed active and passive hand movements while lying in the MRI scanner. During movement execution (active and passive), participants saw either a real-time video of their current movement (“self”) or someone else’s hand moving in accordance with their action (“other”). This manipulation allowed disentangling the effects of movement characteristics (e.g., who is triggering the movement) from visual identity characteristics (whose hand is moving), which both contribute to self-other distinction. Variable delays were inserted between the movement and the images (“self” and “other”), which had to be detected by the participants.
Results
Preliminary results of behavioral performance showed an interaction between group (patients vs. healthy controls) and action execution (active vs. passive): Healthy controls detected less delays in the active condition than in the passive condition, whereas this difference was reduced in patients. In line with this, active vs. passive trials revealed larger BOLD suppression effects in healthy controls than in patients with schizophrenia in multiple brain areas (e.g., lingual gyrus, middle and superior occipital gyrus, posterior parietal cortex, cerebellum). Finally, an interaction effect was found in the thalamus, such that in healthy controls, but not in patients with schizophrenia, this area showed a BOLD suppression effect for active vs. passive movements specific for feedback of one’s own hand.
Discussion
Weaker behavioral and neural suppression effects in patients with schizophrenia (compared to healthy controls) show that actively generated sensory input is not as effectively discarded from further processing, suggesting that efference copy-based predictive mechanisms are impaired in patients with schizophrenia. Furthermore, BOLD suppression in the thalamus was not modulated by hand identity in patients with schizophrenia, indicating that predictive processing in schizophrenia might not take the identity of the seen body part into account.
The emulation theory of representation: Motor control, imagery, and perception
