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Type: Artigo
Title: Reassessment Of Non-monosynaptic Excitation From The Motor Cortex To Motoneurons In Single Motor Units Of The Human Biceps Brachii
Author: Nakajima
Tsuyoshi; Tazoe
Toshiki; Sakamoto
Masanori; Endoh
Takashi; Shibuya
Satoshi; Elias
Leonardo A.; Mezzarane
Rinaldo A.; Komiyama
Tomoyoshi; Ohki
Abstract: Corticospinal excitation is mediated by polysynaptic pathways in several vertebrates, including dexterous monkeys. However, indirect non-monosynaptic excitation has not been clearly observed following transcranial electrical stimulation (TES) or cervicomedullary stimulation (CMS) in humans. The present study evaluated indirect motor pathways in normal human subjects by recording the activities of single motor units (MUs) in the biceps brachii (BB) muscle. The pyramidal tract was stimulated with weak TES, CMS, and transcranial magnetic stimulation (TMS) contralateral to the recording side. During tasks involving weak co-contraction of the BB and hand muscles, all stimulation methods activated MUs with short latencies. Peristimulus time histograms (PSTHs) showed that responses with similar durations were induced by TES (1.9 +/- 1.4 ms) and CMS (2.0 +/- 1.4 ms), and these responses often showed multiple peaks with the PSTH peak having a long duration (65.3% and 44.9%, respectively). Such long-duration excitatory responses with multiple peaks were rarely observed in the finger muscles following TES or in the BB following stimulation of the Ia fibers. The responses obtained with TES were compared in the same 14 BB MUs during the co-contraction and isolated BB contraction tasks. Eleven and three units, respectively, exhibited activation with multiple peaks during the two tasks. In order to determine the dispersion effects on the axon conduction velocities (CVs) and synaptic noise, a simulation study that was comparable to the TES experiments was performed with a biologically plausible neuromuscular model. When the model included the monosynaptic-pyramidal tract, multiple peaks were obtained in about 34.5% of the motoneurons (MNs). The experimental and simulation results indicated the existence of task-dependent disparate inputs from the pyramidal tract to the MNs of the upper limb. These results suggested that intercalated interneurons are present in the spinal cord and that these interneurons might be equivalent to those identified in animal experiments.
Subject: Pyramidal Tract
Transcranial Electrical Stimulation (tes)
Transcranial Magnetic Stimulation (tms)
Primary Motor Cortex (m1)
Motor Unit
Editor: Frontiers Media SA
Citation: Frontiers In Human Neuroscience. Frontiers Media Sa, v. 11, p. , 2017.
Rights: aberto
Identifier DOI: 10.3389/fnhum.2017.00019
Date Issue: 2017
Appears in Collections:Unicamp - Artigos e Outros Documentos

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