title: Long-latency, inhibitory spinal pathway to ankle flexors activated by homonymous group 1 afferents.
abstract: Inhibitory feedback from sensory pathways is important for controlling movement. Here, we characterize, for the first time, a long-latency, inhibitory spinal pathway to ankle flexors that is activated by low-threshold homonymous afferents. To examine this inhibitory pathway in uninjured, healthy participants, we suppressed motor-evoked potentials (MEPs), produced in the tibialis anterior (TA), by a prior stimulation to the homonymous common peroneal nerve (CPN). The TA MEP was suppressed by a triple-pulse stimulation to the CPN, applied 40, 50, and 60 ms earlier and at intensities of 0.5-0.7 times motor threshold (average suppression of test MEP was 33%). Whereas the triple-pulse stimulation was below M-wave and H-reflex threshold, it produced a long-latency inhibition of background muscle activity, approximately 65-115 ms after the CPN stimulation, a time period that overlapped with the test MEP. However, not all of the MEP suppression could be accounted for by this decrease in background muscle activity. Evoked responses from direct activation of the corticospinal tract, at the level of the brain stem or thoracic spinal cord, were also suppressed by low-threshold CPN stimulation. Our findings suggest that low-threshold muscle and cutaneous afferents from the CPN activate a long-latency, homonymous spinal inhibitory pathway to TA motoneurons. We propose that inhibitory feedback from spinal networks, activated by low-threshold homonymous afferents, helps regulate the activation of flexor motoneurons by the corticospinal tract.
authors.affiliation: Department of Biomedical Engineering, University of Alberta, Edmonton, Canada; Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada.
authors.forename: Ephrem T
authors.initials: ET
authors.lastname: Zewdie
authors.affiliation: Department of Surgery, University of Alberta, Edmonton, Canada; Centre for Neuroscience, University of Alberta, Edmonton, Canada; Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada.
authors.forename: Francois D
authors.initials: FD
authors.lastname: Roy
authors.affiliation: Centre for Neuroscience, University of Alberta, Edmonton, Canada;
authors.forename: Yoshino
authors.initials: Y
authors.lastname: Okuma
authors.affiliation: Department of Physical Therapy, University of Alberta, Edmonton, Canada; Centre for Neuroscience, University of Alberta, Edmonton, Canada; Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Canada; and.
authors.forename: Jaynie F
authors.initials: JF
authors.lastname: Yang
authors.affiliation: Department of Biomedical Engineering, University of Alberta, Edmonton, Canada; Centre for Neuroscience, University of Alberta, Edmonton, Canada; Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Canada monica.gorassini@ualberta.ca.
authors.forename: Monica A
authors.initials: MA
authors.lastname: Gorassini
mesh_terms: D000328:Adult; D000842:Ankle / Q000502:physiology*; D001933:Brain Stem / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D010543:Peroneal Nerve / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology; D012879:Skin Physiological Phenomena; D013116:Spinal Cord / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: common peroneal nerve; spinal inhibition; tibialis anterior