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Convergent Spinal Circuits Facilitating Human Wrist Flexors

Lookup NU author(s): Stefane Aguiar, Professor Stuart BakerORCiD



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


Non-invasive assessment of spinal circuitry in humans is limited, especially for Ib pathways in the upper limb. We developed a protocol in which we evoke the H-reflex in flexor carpi radialis (FCR) by median nerve stimulation and condition it with electrical stimulation above motor threshold over the extensor carpi radialis (ECR) muscle belly. Eighteen healthy adults (eight male, ten female) took part in the study. There was a clear reflex facilitation at 30 ms inter-stimulus interval (ISI), and suppression at 70 ms ISI, which was highly consistent across subjects. We investigated two hypotheses of the possible source of the facilitation: (i) ECR Ib afferents from Golgi tendon organs, activated by the twitch following ECR stimulation, and (ii) FCR afferents, from spindles and/or Golgi tendon organs, activated by the wrist extension movement that follows ECR stimulation. Several human and monkey experiments indicated a role for both of these sets of afferents. Our results provide evidence for a spinal circuit in which flexor motoneurons receive convergent excitatory input from flexor afferents as well as from extensor Ib afferents; this circuit can be straightforwardly assessed non-invasively in humans.

Publication metadata

Author(s): Aguiar SA, Baker SN

Publication type: Article

Publication status: Published

Journal: Journal of Neuroscience

Year: 2018

Volume: 38

Issue: 16

Pages: 3929-3938

Print publication date: 18/04/2018

Online publication date: 21/03/2018

Acceptance date: 31/01/2018

Date deposited: 27/03/2018

ISSN (print): 0270-6474

ISSN (electronic): 1529-2401

Publisher: Society for Neuroscience


DOI: 10.1523/JNEUROSCI.1870-17.2018


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Funder referenceFunder name
Wellcome Trust