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Different phase delays of peripheral input to primate motor cortex and spinal cord promote cancellation at physiological tremor frequencies

Lookup NU author(s): Sasa Kozelj, Professor Stuart Baker

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Neurons in the spinal cord and motor cortex (M1) are partially phase-locked to cycles of physiological tremor, but with opposite phases. Convergence of spinal and cortical activity onto motoneurons may thus produce phase cancellation and a reduction in tremor amplitude. The mechanisms underlying this phase difference are unknown. We investigated coherence between spinal and M1 activity with sensory input. In two anesthetized monkeys, we electrically stimulated the medial, ulnar, deep radial, and superficial radial nerves; stimuli were timed as independent Poisson processes (rate 10 Hz). Single units were recorded from M1 (147 cells) or cervical spinal cord (61 cells). Ninety M1 cells were antidromically identified as pyramidal tract neurons (PTNs); M1 neurons were additionally classified according to M1 subdivision (rostral/caudal, M1r/c). Spike-stimulus coherence analysis revealed significant coupling over a broad range of frequencies, with the strongest coherence at <50 Hz. Delays implied by the slope of the coherence phase-frequency relationship were greater than the response onset latency, reflecting the importance of late response components for the transmission of oscillatory inputs. The spike-stimulus coherence phase over the 6-13 Hz physiological tremor band differed significantly between M1 and spinal cells (phase differences relative to the cord of 2.72 +/- 0.29 and 1.72 +/- 0.37 radians for PTNs from M1c and M1r, respectively). We conclude that different phases of the response to peripheral input could partially underlie antiphase M1 and spinal cord activity during motor behavior. The coordinated action of spinal and cortical feedback will act to reduce tremulous oscillations, possibly improving the overall stability and precision of motor control.


Publication metadata

Author(s): Kozelj S, Baker SN

Publication type: Article

Publication status: Published

Journal: Journal of Neurophysiology

Year: 2014

Volume: 111

Issue: 10

Pages: 2001-2016

Print publication date: 15/05/2014

Online publication date: 26/02/2014

Acceptance date: 24/02/2014

Date deposited: 15/10/2014

ISSN (print): 0022-3077

ISSN (electronic): 1522-1598

Publisher: American Physiological Society

URL: http://dx.doi.org/10.1152/jn.00935.2012

DOI: 10.1152/jn.00935.2012


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