Abstract
Background
Neuromuscular
electrical stimulation (NMES) is extensively used in stroke motor
rehabilitation. How it promotes motor recovery remains only partially
understood. NMES could change muscular properties, produce altered
sensory inputs, and modulate fluctuations of cortical activities; but
the potential contribution from cortico-muscular couplings during NMES
synchronized with dynamic movement has rarely been discussed.
Method
We
investigated cortico-muscular interactions during passive, active, and
NMES rhythmic pedaling in healthy subjects and chronic stroke survivors.
EEG (128 channels), EMG (4 unilateral lower limb muscles) and movement
parameters were measured during 3 sessions of constant-speed pedaling.
Sensory-level NMES (20 mA) was applied to the muscles, and cyclic
stimulation patterns were synchronized with the EMG during pedaling
cycles. Adaptive mixture independent component analysis was utilized to
determine the movement-related electro-cortical sources and the source
dipole clusters. A directed cortico-muscular coupling analysis was
conducted between representative source clusters and the EMGs using
generalized partial directed coherence (GPDC). The bidirectional GPDC
was compared across muscles and pedaling sessions for post-stroke and
healthy subjects.
Results
Directed
cortico-muscular coupling of NMES cycling was more similar to that of
active pedaling than to that of passive pedaling for the tested muscles.
For healthy subjects, sensory-level NMES could modulate GPDC of both
ascending and descending pathways. Whereas for stroke survivors, NMES
could modulate GPDC of only the ascending pathways.
Conclusions
By
clarifying how NMES influences neuromuscular control during pedaling in
healthy and post-stroke subjects, our results indicate the potential
limitation of sensory-level NMES in promoting sensorimotor recovery in
chronic stroke survivors.
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