The effects of neuromuscular electrical stimulation on corticomuscular coherence in patients with stroke

Neuromuscular electrical stimulation (NMES) applied in the periphery can elicit strong sensory input that could modulate the excitability of contralateral primary sensorimotor cortex. Here we want to understand the immediate effects of 1-session NMES on the coherence between brain and muscles and motor performance in patients with stroke. EEG (16 channels) of bilateral sensorimotor cortical area and surface EMG of the stroke-affected flexor pollicis brevis were recorded while the subjects performed a 20-second steady hold contraction at 50% maximal voluntary before and after a 40-minute electrical stimulation session on median nerve. The stimulation (1-ms rectangular pulse, 100 Hz) was delivered with a 20 s-on-20 s-off cycle. The intensity was set at the subjects’ highest tolerable level without causing pain. Our preliminary results from 8 stroke subjects (3 in sham-ES group) showed that coherence between contralateral primary motor cortex (hand area) and flexor pollicis brevis muscle increased in lower gamma-band after using NMES. Subjects performed better in force-maintenance task after receiving NMES. Based on our preliminary results, NMES appears to increase corticomuscular coherence and motor performance. Greater gamma-band coherence after repetitive electrical stimulation might indicate enhanced cortical activity level and sensorimotor integration during voluntary motor task.