Somatosensory Dysfunction as the Underlying Mechanism of Upper Limbs Motor Blocks in People With Parkinson's Disease

Motor blocks during gait and upper limb movements (FOULs) are a disabling and common motor impairment in mild to severe stages of Parkinson's disease (PD). However, the main mechanism underlying these phenomena is still an open debate. Apart from the motor correlates, cognitive-attentional impairment and somatosensory deficits (especially in the proprioceptive system) may underlie these motor blocks. The current study aims to unravel whether the proprioceptive system is involved by manipulating task-relevant or non-relevant proprioceptive stimuli. Hence, the main aims of this study are: (i) to assess the somatosensory function in people with PD that experience freezing of gait FOG and (ii) to investigate the effects of manipulating both proprioception and attentional resources on FOUL severity. Forty-five people will be assigned to three age-matched groups (N=15 each): healthy elderly, PD patients that experience FOG (FOG+) and PD patients that do not experience FOG. Cutaneous sensory function and kinesthetic ability will be assessed by means of standardized user-friendly methods and precise repositioning measures using the VICON motion analysis. Additionally, participants will perform a newly developed task that can successfully elicit FOULs (a handwriting freezing-provoking task) on a custom tablet (Heremans et al 2015). The task will be performed without and with the use of muscle vibration (a well-known method to stimulate the proprioceptive system). The investigators will manipulate both the timing of vibration (relevant - after FOUL onset; or non-relevant: before FOUL onset) and the region of stimulation (neutral: on a bone-mark where there is little if any proprioceptive stimulation; and on a non-neutral spot: on the forearm muscles). It is believed that FOG+ will present with worse somatosensory function than those who do not experience motor blocks (especially in the proprioceptive system). Additionally, the Investigators expect a reduction in FOUL severity (e.g. FOUL duration) when vibration is applied in a task-relevant way, independently of the region stimulated. In contrast, it is also expected that when vibration is applied in a non-relevant way and it may act as a distractor, FOUL duration will increase. This study will thus be able to distinguish between the contribution of attentional and proprioceptive resources to the mechanism of motor blocks in PD.