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Yoshimoto T, Nito M, Hashizume W, Shimada K, Sato T, Shindo M, Naito A. Mutual oligosynaptic inhibition of group Ia afferents between the anterior and posterior parts of the deltoid in humans. Exp Brain Res 2024; 242:1481-1493. [PMID: 38702470 DOI: 10.1007/s00221-024-06834-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2023] [Accepted: 04/09/2024] [Indexed: 05/06/2024]
Abstract
The anterior (DA) and posterior parts of the deltoid (DP) show alternating contraction during shoulder flexion and extension movements. It is expected that an inhibitory spinal reflex between the DA and DP exists. In this study, spinal reflexes between the DA and DP were examined in healthy human subjects using post-stimulus time histogram (PSTH) and electromyogram averaging (EMG-A). Electrical conditioning stimulation was delivered to the axillary nerve branch that innervates the DA (DA nerve) and DP (DP nerve) with the intensity below the motor threshold. In the PSTH study, the stimulation to the DA and DP nerves inhibited (decrease in the firing probability) 31 of 54 DA motor units and 31 of 51 DP motor units. The inhibition was not provoked by cutaneous stimulation. The central synaptic delay of the inhibition between the DA and DP nerves was 1.5 ± 0.5 ms and 1.4 ± 0.4 ms (mean ± SD) longer than those of the homonymous facilitation of the DA and DP, respectively. In the EMG-A study, conditioning stimulation to the DA and DP nerves inhibited the rectified and averaged EMG of the DP and DA, respectively. The inhibition diminished with tonic vibration stimulation to the DA and DP and recovered 20-30 min after vibration removal. These findings suggest that oligo(di or tri)-synaptic inhibition mediated by group Ia afferents between the DA and DP exists in humans.
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Affiliation(s)
- Takuya Yoshimoto
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan
- Department of Judo Seifuku Therapy, Meiji University of Integrative Medicine, Nantan, Japan
| | - Mitsuhiro Nito
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan.
- Department of Occupational Therapy, Yamagata Prefectural University of Health Sciences, 260 Kamiyanagi, Yamagata, 990-2212, Japan.
| | - Wataru Hashizume
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan
| | - Kazuto Shimada
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan
- Department of Occupational Therapy, Yamagata College of Medical Arts and Science, Yamagata, Japan
| | - Tomomi Sato
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan
- Department of Physical Therapy, Yamagata College of Medical Arts and Science, Yamagata, Japan
| | | | - Akira Naito
- Department of Anatomy and Structural Science, Yamagata University School of Medicine, Yamagata, Japan
- Department of Physical Therapy, Tohoku Bunka Gakuen University, Sendai, Japan
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Nito M, Yoshimoto T, Hashizume W, Shindo M, Naito A. Monosynaptic facilitation of motoneurons innervating intrinsic hand muscles mediated by group Ia afferents from the extensor carpi radialis in humans. Physiol Rep 2022; 10:e15431. [PMID: 36017963 PMCID: PMC9413870 DOI: 10.14814/phy2.15431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 07/28/2022] [Accepted: 07/31/2022] [Indexed: 06/15/2023] Open
Abstract
The projection pattern of low-threshold afferents from the extensor carpi radialis (ECR) to motoneurons supplying intrinsic hand muscles was investigated using the post-stimulus time-histogram (PSTH) and electromyogram-averaging (EMG-A) methods. Electrical conditioning stimulation was applied to the radial nerve branch innervating the ECR. In the PSTH study, changes in the firing probability of single motor units following the stimulation were examined. An early and significant peak (facilitation) was induced in the motoneurons innervating the muscles, but the facilitation was induced infrequently. The central latency of the facilitation was equivalent to that of homonymous facilitation through monosynaptic path in the spinal cord. In the EMG-A study, changes in the rectified and averaged electromyograms following the conditioning stimulation were examined. An early and significant peak (facilitation) was also induced. The facilitation disappeared after withdrawal of the vibration to the ECR muscle belly. Cutaneous nerve stimulation overlaying ECR never induced such facilitation in the PSTH and EMG-A studies. These findings suggest that monosynaptic facilitation mediated by group Ia afferents of ECR to the motoneurons supplying intrinsic hand muscles exists in humans, but the connection seems to be weak. This weakness might allow manipulatory movements of the hand.
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Affiliation(s)
- Mitsuhiro Nito
- Department of Anatomy and Structural ScienceYamagata University School of MedicineYamagataJapan
| | - Takuya Yoshimoto
- Department of Anatomy and Structural ScienceYamagata University School of MedicineYamagataJapan
| | - Wataru Hashizume
- Department of Anatomy and Structural ScienceYamagata University School of MedicineYamagataJapan
| | | | - Akira Naito
- Department of Anatomy and Structural ScienceYamagata University School of MedicineYamagataJapan
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