Proximal-to-distal compensation is commonly observed in upper extremity(UE) after stroke, mainly due to the impaired fine motor control in hand joints. However, little is known on its related neural reorganization. This study investigated the pathway-specific corticomuscular interaction in proximal-to-distal compensation during fine motor control of finger extension post-stroke by directed corticomuscular coherence(dCMC).
We recruited 14 chronic stroke participants and 11 unimpaired controls. Electroencephalogram(EEG) from the sensorimotor area was concurrently recorded with electromyography(EMG) from extensor digitorum(ED), flexor digitorum(FD), triceps brachii(TRI) and biceps brachii(BIC) muscles in both sides of the stroke participants and in the dominant(right) side of the controls during a unilateral isometric finger extension task at 20% maximal voluntary contractions. The dCMC was then analyzed in both descending(EEG→EMG) and ascending pathways(EMG→EEG) via directed coherence. It was also analyzed in the respective stable and less-stable periods subdivided from the whole movement period to investigate the fine motor control. Finally, the corticomuscular conduction time was estimated by dCMC phase delay.
Descending dCMC in the affected limb was significantly lower in distal muscles(ED and FD) than BIC (P<0.05). The descending dominance(significantly higher descending dCMC than the ascending, P<0.05) was in proximal muscles(BIC and TRI) in the affected limb but in distal muscles in the control group. In the less-stable period, ED and FD in the affected limb had significantly lower EMG stability and significantly higher ascending dCMC(P<0.05) without significant change in the descending compared with the control. Significantly prolonged descending conduction time(~38.8 ms) was found in ED in the affected limb than the unaffected(~26.94 ms) and control limbs(~25.74 ms) (P<0.05).
The proximal-to-distal UE compensation during fine motor control post-stroke presented altered descending dominance from the distal to proximal UE, increased ascending feedback from the distal for fine motor control, and prolonged descending conduction time in the agonist muscle.

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