High density EMG investigation of stimulus-driven muscle responses associated with covert orienting

We hypothesize that freezing of gait in Parkinson*s disease (PD) may in part be
explained by bilaterally simultaneous orienting responses accompanied by
short-latency reflex-like activity in axial muscles. The bilaterally
simultaneous nature of these responses interferes with the normally alternating
activation pattern of these muscles during walking, thus inducing freezing. To
evaluate this hypothesis in PD, we will investigate the characteristics of the
short-latency muscle response in the pectoralis muscle, where the response is
most easily picked up with surface EMG. We hypothesize that there is a
disinhibition of the reflex in PD, evidenced by a higher amplitude of the
reflex, possibly also a shorter latency. Confirmation of this hypothesis
provides the basis for further experiments to test the hypothesized
pathophysiology in a more detailed fashion.

Primary Objective: To determine the characteristics of the short-latency muscle
response (SLR) in patients with Parkinson*s disease, in comparison to
age-matched healthy controls.

Secondary Objective(s): To correlate the characteristics of the SLR with
behaviour in an anti-reach task, to address a possible relation with impaired
response inhibition.

The investigation concerns an observational study in patients with Parkinson*s
disease and age-matched healthy volunteers. The study is of an exploratory
nature, using high-density surface EMG to record reflex responses in the m.
pectoralis during an anti-reaching task. The study assesses the presence, the
amplitude, and the latency of the reflex responses and their sensitivity to the
direction of visual orientation. The investigation will be carried out from
February to December 2016. The investigation is conducted at the Social Science
Faculty of the Radboud University, in the Sensorimotor Research lab (Prof.
Medendorp) with neurological involvement from the Dept. of Neurology Radboud
UMC.

Participants will be subjected to a single 2-hour experimental session in which
they perform an anti-reach task with a robotic manipulandum. The task is simple
and not physically or cognitively demanding. During the task surface EMG is
recorded from the right m. pectoralis using an electrode grid with 64 electrode
contacts. Application of the electrode array and the recording are painless and
do not involve any health risk.