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      Effects of muscle relaxation on sustained contraction of ipsilateral remote muscle

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          Abstract

          The objective of this study was to clarify the temporal change of muscle activity during relaxation of ipsilateral remote muscles. While participants maintained a constant right wrist extensor isometric force, they dorsiflexed the ipsilateral ankle from resting position or relaxed from dorsiflexed position in response to an audio signal. The wrist extensor force magnitude increased in the 0–400 msec period after the onset of foot contraction compared to that of the resting condition ( <  0.05). On the other hand, wrist extensor force magnitude and electromyographic (EMG) activity decreased in the 0–400 msec period after the onset of ankle dorsiflexion compared to that of the resting condition ( <  0.05). Our findings suggest that foot muscle relaxation induces temporal reduction in hand muscle EMG activity and force magnitude.

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          Most cited references28

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          Attentional requirements of learning: Evidence from performance measures

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            Basic mechanisms of TMS.

            Transcranial magnetic stimulation (TMS) is now established as an important noninvasive measure for neurophysiologic investigation of the central and peripheral nervous systems in humans. Magnetic stimulation can be used for stimulating peripheral nerves with a similar mechanism of activation as for electrical stimulation. When TMS is applied to the cerebral cortex, however, some features emerge that distinguish it from transcranial electrical stimulation. One of the most important features is designated the D and I wave hypothesis, which is now widely accepted as a mechanism of TMS of the motor cortex. Transcranial electrical stimulation excites the pyramidal tract axons directly, either at the initial segment of the neuron or at proximal internodes in the subcortical white matter, giving rise to D (direct) waves, whereas TMS excites the pyramidal neurons transsynaptically, giving rise to I (indirect) waves. There are still other phenomena with mechanisms that remain to be elucidated. First, not only excitatory effects but also inhibitory effects can be elicited by TMS of the cerebral cortex (e.g., the silent period and intracortical inhibition). The inhibitory effect may also be used to investigate cerebral functions other than the motor cortex, such as the visual, sensory cortices, and the frontal eye field, from which no overt response like the motor evoked potential can be elicited. Second, there is an abundance of intraregional functional connectivities among different cortical areas that can also be revealed by TMS, or TMS in combination with neuroimaging techniques. Last, repetitive transcranial stimulation exerts a lasting effect on brain function even after the stimulation has ceased. With further investigation of the neural mechanisms of TMS, these techniques will open up new possibilities for investigating the physiologic function of the brain as well as opportunities for clinical application.
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              Changes in the balance between motor cortical excitation and inhibition in focal, task specific dystonia.

              Transcranial magnetic stimulation has been used in a double pulse paradigm to investigate the excitability of intrinsic motor cortical circuits in 15 patients with focal task specific dystonia of the right hand and a group of eight age matched controls. The left hemisphere was examined in five patients; in the remainder, both hemispheres were tested. There was no significant difference in stimulation threshold between patients and controls nor between the left and right hemispheres in the patients. There was a significant decrease in early corticocortical suppression when comparing stimulation of the left hemisphere in the patients and controls at interstimulus intervals of 1-15 ms (P < 0.01). There was no difference in the amount of suppression in the right and left hemispheres of the patients. It is concluded that in focal task specific dystonia there is shift in the balance between excitation and inhibition in local circuits of the motor cortex which leads to a net decrease in the amount of short latency suppression. These changes reflect disturbed basal ganglia input to the motor cortex. Reduced excitability of cortical inhibitory circuits may be one factor which contributes to the excessive and inappropriate muscle contraction which occurs during fine motor tasks in patients with focal dystonia.
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                Author and article information

                Journal
                Physiol Rep
                Physiol Rep
                phy2
                Physiological Reports
                John Wiley & Sons, Ltd (Chichester, UK )
                2051-817X
                2051-817X
                November 2015
                26 November 2015
                : 3
                : 11
                : e12620
                Affiliations
                [1 ]Faculty of Sport Sciences, Waseda University Tokorozawa, Japan
                [2 ]Japan Society for the Promotion of Science Chiyoda-ku, Japan
                Author notes
                Correspondence Kouki Kato, Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192, Japan., Tel: +81-4-2947-6826, Fax: +81-4-2947-6826, E-mail: kouki0104@ 123456gmail.com

                Funding Information This work was supported by a grant for the fellows of the Japan Society for the Promotion of Science (JSPS) awarded to K. K. and by a Grant-in-Aid from the Global COE “Sport Sciences for the Promotion of Active Life,” Waseda University, from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

                Article
                10.14814/phy2.12620
                4673648
                26611464
                5b32219c-d9bc-4d8d-bb3c-e6eb9af53539
                © 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 21 July 2015
                : 05 October 2015
                : 07 October 2015
                Categories
                Original Research

                coordination,inhibition,multilimb movements
                coordination, inhibition, multilimb movements

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