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Suzuki S, Nakajima T, Irie S, Ariyasu R, Ohtsuka H, Komiyama T, Ohki Y. Subcortical Contribution of Corticospinal Transmission during Visually Guided Switching Movements of the Arm. Cereb Cortex 2021; 32:380-396. [PMID: 34231853 DOI: 10.1093/cercor/bhab214] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Revised: 05/28/2021] [Accepted: 06/10/2021] [Indexed: 11/12/2022] Open
Abstract
In animal experiments, the indirect corticospinal tract (CST) system via cervical interneurons has been shown to mediate motor commands for online adjustment of visuomotor behaviors, such as target-reaching. However, it is still unclear whether the similar CST system functions to perform similar motor behaviors in humans. To clarify this, we investigated changes in motor-evoked potentials (MEPs) in the elbow muscles following transcranial magnetic stimulation, transcranial electrical stimulation, or cervicomedullary stimulation while participants executed target-reaching and switching movements. We found that the MEP, whether elicited cortically or subcortically, was modulated depending on the direction of the switching movements. MEP facilitation began around the onset of the switching activities in an agonist muscle. Furthermore, ulnar nerve-induced MEP facilitation, which could be mediated by presumed cervical interneuronal systems, also increased at the onset of MEP facilitation. In a patient with cortical hemianopsia who showed switching movements in the scotoma, the MEPs were facilitated just before the switching activities. Our findings suggested that CST excitation was flexibly tuned with the switching movement initiation, which could partly take place in the subcortical networks, including the presumed cervical interneuronal systems.
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Affiliation(s)
- Shinya Suzuki
- Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan.,School of Rehabilitation Sciences, Health Sciences University of Hokkaido, Hokkaido, Japan
| | - Tsuyoshi Nakajima
- Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan
| | - Shun Irie
- Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan
| | - Ryohei Ariyasu
- Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan
| | - Hiroyuki Ohtsuka
- Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan
| | - Tomoyoshi Komiyama
- Division of Health and Sports Sciences, Faculty of Education, Chiba University, Chiba, Japan.,Division of Health and Sports Education, The United Graduate School of Education, Tokyo Gakugei University, Tokyo, Japan
| | - Yukari Ohki
- Department of Integrative Physiology, Kyorin University School of Medicine, Tokyo, Japan
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Fisher KM, Baker SN. A Re-evaluation of Whether Non-monosynaptic Homonymous H Reflex Facilitation Tests Propriospinal Circuits. Front Syst Neurosci 2021; 15:641816. [PMID: 33833670 PMCID: PMC8021928 DOI: 10.3389/fnsys.2021.641816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 03/02/2021] [Indexed: 11/13/2022] Open
Abstract
The C3-C4 propriospinal system is an important pathway mediating movement in cats; it contributes to movements in primates (including humans), and may have a role in recovery after lesion. Validated clinical tests of this system would find many applications, therefore we sought to test whether non-monosynaptic homonymous facilitation of the forearm flexor H reflex is mediated solely via a C3-C4 propriospinal pathway. In one anesthetized macaque monkey, median nerve stimulation elicited an H reflex in the flexor carpi radialis (FCR). Median nerve conditioning stimuli at sub-threshold intensities facilitated the H reflex, for inter-stimulus intervals up to 30 ms. Successive spinal surgical hemisections were then made. C2 lesion left the homonymous facilitation intact, suggesting mediation by spinal, not supraspinal pathways. Facilitation also remained after a second lesion at C5, indicating a major role for segmental (C7-C8) rather than propriospinal (C3-C4) interneurons. In separate experiments in five healthy human subjects, a threshold tracking approach assessed changes in peripheral axon excitability after conditioning stimulation. This was found to be enhanced up to 20 ms after the conditioning stimulus, and could partly, although not completely, underlie the H reflex facilitation seen. We conclude that homonymous facilitation of the H reflex in FCR can be produced by segmental spinal mechanisms, as well as by a supranormal period of nerve excitability. Unfortunately, this straightforward test cannot therefore be used for selective assessment of propriospinal circuits.
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Affiliation(s)
- Karen M. Fisher
- Henry Wellcome Building, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Stuart N. Baker
- Henry Wellcome Building, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
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Nakajima T, Ohtsuka H, Irie S, Suzuki S, Ariyasu R, Komiyama T, Ohki Y. Visual information increases the indirect corticospinal excitation via cervical interneurons in humans. J Neurophysiol 2021; 125:828-842. [PMID: 33502947 DOI: 10.1152/jn.00425.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Modulatory actions of inputs from the visual system to cervical interneurons (IN) for arm muscle control are poorly understood in humans. In the present study, we examined whether visual stimulation modulates the excitation of cervical IN systems mediating corticospinal tract (CST) inputs to biceps brachii (BB). Twenty-eight healthy volunteers were seated, and electromyogram recordings from the BB were performed across six experiments, each with discrete objectives. A flash stimulator for visual stimulation (50-μs duration) was placed 60 cm from the participant's eye. The CST was stimulated with transcranial magnetic/electrical stimulation (TMS/TES, respectively) contralateral to the recording site. Visual stimulation with TMS/TES was randomly delivered during weak tonic BB contractions. Single TMS/TES-induced motor-evoked potentials (MEPs) were markedly enhanced from 60-100 ms after visual stimulation compared with the control condition. The MEPs were significantly increased by combining the electrical stimulation of the ulnar nerve at the wrist [7.5-12 ms of nerve stimulation (NERVE)/TMS interval] with and without visual stimulation compared with the algebraic summation of responses obtained with either TMS or NERVE. Interestingly, the combined stimulation-induced MEP facilitation was significantly increased after visual stimulation compared with the control. Single motor unit (MU) recording also revealed the further enhancement of combined stimulation effects on the firing probabilities of MU during visual stimulation, which was observed in the peaks of the peristimulus time histogram, 1-2 ms later than the onset latency. The present findings suggest that visual stimulation facilitates the oligosynaptic CST excitation of arm motoneurons mediated by the cervical IN system.NEW & NOTEWORTHY To date, little is known about how visual information modulates the human cervical motor systems, including the presumed interneuron (IN) circuitry. This study demonstrates that photic visual stimulation influences presumed oligosynaptic corticospinal transmission to arm motoneurons, which are mediated by cervical INs. In animals, these systems are known to be crucial for visually guided switching movements, and similar visual input systems to INs may exist in humans.
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Affiliation(s)
- Tsuyoshi Nakajima
- Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan
| | - Hiroyuki Ohtsuka
- Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan
| | - Shun Irie
- Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan
| | - Shinya Suzuki
- Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan.,Department of Physical Therapy, School of Rehabilitation Sciences, Health Sciences University of Hokkaido, Tobetsu-cho, Hokkaido, Japan
| | - Ryohei Ariyasu
- Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan
| | - Tomoyoshi Komiyama
- Division of Health and Sports Education, The United Graduate School of Education, Tokyo Gakugei University, Koganei City, Tokyo, Japan.,Division of Health and Sports Sciences, Faculty of Education, Chiba University, Chiba City, Chiba, Japan
| | - Yukari Ohki
- Department of Integrative Physiology, Kyorin University School of Medicine, Mitaka City, Tokyo, Japan
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