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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Reassessment of Non-Monosynaptic Excitation from the Motor Cortex to Motoneurons in Single Motor Units of the Human Biceps Brachii

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Author(s):
Nakajima, Tsuyoshi ; Tazoe, Toshiki ; Sakamoto, Masanori ; Endoh, Takashi ; Shibuya, Satoshi ; Elias, Leonardo A. ; Mezzarane, Rinaldo A. ; Komiyama, Tomoyoshi ; Ohki, Yukari
Total Authors: 9
Document type: Journal article
Source: FRONTIERS IN HUMAN NEUROSCIENCE; v. 11, JAN 30 2017.
Web of Science Citations: 6
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. (AU)

FAPESP's process: 13/10433-1 - Discharge properties of motor units from ankle extensor and flexor muscles during sinusoidal modulation of the joint torque and angle
Grantee:Leonardo Abdala Elias
Support Opportunities: Scholarships in Brazil - Post-Doctoral
FAPESP's process: 12/05304-5 - Effects of cutaneous activation on contralateral reflex modulation during gait in humans
Grantee:Rinaldo André Mezzarane
Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
FAPESP's process: 09/15802-0 - Modelling and simulation of torque control by proprioceptive feedback through the nervous system: application to postural control
Grantee:Leonardo Abdala Elias
Support Opportunities: Scholarships in Brazil - Doctorate