Distinct patterns of visuo-tactile and visuo-motor body-related integration in Parkinson's disease

Multisensory integration (MSI) deficits in patients with Parkinson's Disease (PD) have recently attracted growing interest in both clinical and research realms, MSI being crucial in maintaining well-coordinated responses to external stimuli. In this framework, we exploited the Rubber Hand Illusion (RHI), an experimental procedure that induces healthy individuals to embody a fake hand by integrating multisensory body-related cues, to address potential alterations of the embodiment phenomenon in PD. Specifically, we leveraged a visuo-tactile (VT; Experiment 1) and a visuo-motor (VM; Experiment 2) RHI version and applied it to 32 PD patients and age-matched controls. Classical RHI measures (i.e., ownership and agency questionnaires, proprioceptive drift) were collected. Questionnaires revealed typical VT- and VM-RHI patterns in patients, although diminished as compared to controls. Crucially, proprioceptive drift showed an abolishment of VM- (but not VT-) RHI effect in patients, advocating for a channel-specific embodiment abnormality that emerged only when the motor system, involved in the pathology, was challenged by the RHI. Interestingly, such a deficit emerged specifically when proprioceptive drift, engaging a motor response, was considered as a measure. We speculatively interpret this finding in light of the neural degeneration of basal ganglia in PD, being these structures engaged in visuo-motor integration.