Human Cervical Epidural Spinal Electrogram Topographically Maps Distinct Volitional Movements.

Little is known about the electrophysiologic activity of the intact human spinal cord during volitional movement. We analyzed epidural spinal recordings from a total of 5 human subjects of both sexes during a variety of upper extremity movements and found that these spinal epidural electrograms contain spectral information distinguishing periods of movement, rest, and sensation. Cervical epidural electrograms also contained spectral changes time-locked with movement. We found that these changes were primarily associated with increased power in the theta (4-8 Hz) band, feature increased theta-gamma phase-amplitude coupling, and that this increase in theta power can be used to topographically map distinct upper extremity movements onto the cervical spinal cord in accordance with established myotome maps of the upper extremity. Our findings have implications for the development of neurostimulation protocols and devices focused on motor rehabilitation for the upper extremity and the approach presented here may facilitate spatiotemporal mapping of naturalistic movements.Significance statement The electrophysiology of the human spinal cord remains incompletely characterized. We build on our previous work in describing a novel method of recording spinal epidural electrograms from awake human participants by showing that SEGs (spinal electrograms) recorded from the cervical spinal cord during volitional upper extremity movements demonstrate spectral changes time-locked to movement that feature prominent increase in theta band power, theta-gamma phase-amplitude coupling, and are well delineated from pre-movement baseline. These spectral changes can also be topographically mapped to the cervical spine in a myotome distribution broadly consistent with maps generated from intraoperative stimulation studies in humans and direct stimulation experiments in monkeys. Our methodology may aid in the developing spatiotemporal maps for neurostimulation protocols to recapitulate naturalistic movements.

Human upper extremity motor cortex activity shows distinct oscillatory signatures for stereotyped arm and leg movements.

Introduction: Stepping and arm swing are stereotyped movements that require coordination across multiple muscle groups. It is not known whether the encoding of these stereotyped movements in the human primary motor cortex is confined to the limbs' respective somatotopy. Methods: We recorded subdural electrocorticography activities from the hand/arm area in the primary motor cortex of 6 subjects undergoing deep brain stimulation surgery for essential tremor and Parkinson's disease who performed stepping (all patients) and arm swing (n = 3 patients) tasks. Results: We show stepping-related low frequency oscillations over the arm area. Furthermore, we show that this oscillatory activity is separable, both in frequency and spatial domains, from gamma band activity changes that occur during arm swing. Discussion: Our study contributes to the growing body of evidence that lower extremity movement may be more broadly represented in the motor cortex, and suggest that it may represent a way to coordinate stereotyped movements across the upper and lower extremities.