Afferent Encoding of Central Oscillations in the Monkey Arm

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Abstract
We have investigated whether peripheral afferent fibers could encode the central oscillations that are commonly seen in the primate motor system. We analyzed 52 single afferent recordings from the C8/T1 dorsal root ganglia of two monkeys performing an isometric wrist flexion–extension task. Coherence and directed coherence were calculated between the afferent spikes and forearm EMG. Seven of 52 cells were identified as Group Ia afferents by the production of narrow postspike facilitation in spike-triggered averages of rectified EMG. These identified afferents showed significant coherence, and directed coherence, with EMG over a wide frequency range. By contrast, coherence was weak for a population that showed little directional preference for flexion or extension movements during task performance, and probably contained mainly cutaneous afferents. Oscillations are known to appear in muscle activity; their presence in afferent firing as well implies that central oscillations pass around a peripheral feedback loop and may be involved in sensorimotor integration.