Parkinson's disease may reduce sensitivity to visual-tactile asynchrony irrespective of dopaminergic treatment: Evidence from the rubber hand illusion.

BACKGROUND

The feeling of body ownership relies on the binding of multisensory body-related signals. Various sensory abnormalities have been described in Parkinson's disease (PD).

OBJECTIVE

To assess the rubber hand illusion (RHI) in patients with PD (PwPD) and age-matched healthy controls (CTRL). To evaluate the influence of the dopaminergic system in a PwPD subgroup OFF medication.

METHODS

The RHI paradigm was applied to 42 PwPD and 48 CTRL. In this experimental setup, stroking a visible plastic hand simultaneously with the covered real hand elicits the feeling of ownership over the seen hand. Asynchronous stroking served as a control condition. Proprioceptive bias and an illusion score based on a questionnaire were used as measures of the RHI. Seventeen PwPD additionally underwent the experiments "OFF medication".

RESULTS

Compared to CTRL, PwPD showed higher proprioceptive bias independent of the stroking condition (p = 0.015), and had higher illusion scores in the asynchronous condition (p < 0.05). In PwPD, there were no significant differences between ON- and OFF-medication state.

CONCLUSION

In PwPD, responses to the RHI are less specific with respect to the degree of synchronicity of brushstrokes. This might be attributed to a less stable body representation, internal "noise" during multisensory integration, or a blur of temporal discrimination in PD. The fact that RHI measures did not differ between ON- and OFF-medication states indicates an involvement of non-dopaminergic transmitter systems in this finding.