Spinomuscular coherence in monkeys performing a precision grip task.

We recorded local field potentials (LFPs) from cervical spinal cord (C(5)-C(8)) in monkeys performing a precision grip task and examined their coherence with electromyographic (EMG) activities (spinomuscular coherence) recorded from hand and arm muscles. Among 164 LFP-EMG pairs, significant coherence was found in 34 pairs (21%). We classified the coherence into two groups based on its frequency range, narrowband coherence, and broadband coherence. The narrowband coherence was restricted to discrete frequencies in the range of 14-55 Hz and was widespread throughout the superficial and deep gray matter. In contrast, the broadband coherence distributed between 10 and 95 Hz and was found only in the ventral half of the spinal cord. The narrowband coherence suggests that oscillations, which have been described in many motor control areas of the brain, could also pass though spinal interneurons to affect motor output and sensorimotor integration. On the other hand, the broadband coherence could be a unique feature of spinal motoneuron-muscle physiology.