Attenuated beta rebound to proprioceptive afferent feedback in Parkinson’s disease

Motor symptoms are defining traits in the diagnosis of Parkinsons disease (PD). A crucial component in motor function and control of movements is the integration of efferent signals from the motor network to the peripheral motor system, and afferent proprioceptive sensory feedback. Previous studies have indicated abnormal movement-related cortical oscillatory activity in PD, but the role of the proprioceptive afference on abnormal oscillatory activity in PD has not been elucidated. In the present study, we examine the role of proprioception by studying the cortical processing of proprioceptive stimulation in PD patients, ON/OFF levodopa medication, as compared to that of healthy controls (HC). We used a proprioceptive stimulator that generated precisely controlled passive movements of the index finger and measured the induced cortical oscillatory responses following the proprioceptive stimulation using magnetoencephalography (MEG). Both PD patients and HC showed a typical initial mu/beta-band (8-30 Hz) desynchronization during the passive movement. However, the subsequent beta rebound after the passive movement that was apparent in HC was much attenuated and almost absent in PD patients. Furthermore, we found no difference in the degree of beta rebound attenuation between patients ON and OFF levodopa medication. Our results hence demonstrate a disease-related deterioration in cortical processing of proprioceptive afference in PD, and further suggest that such disease-related loss of proprioceptive function is due to processes outside the dopaminergic system affected by levodopa medication.