TU-115. Transcranial ultrasonic stimulation of the human primary motor cortex
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During exercise, changes occur at many sites in the motor pathway, including the muscle fiber, motoneuron, motor cortex, and “upstream” of the motor cortex. Some of the changes result in fatigue, which can be defined as a decrease in ability to produce maximal muscle force voluntarily. Transcranial magnetic stimulation (TMS) over the human motor cortex reveals changes in both motor evoked potentials (MEPs) and the silent period during and after fatiguing voluntary contractions in normal subjects. The relationship of these changes to loss of force or fatigue is unclear. However, during a sustained maximal contraction TMS evokes extra force from the muscle and thus demonstrates the development of suboptimal output from the motor cortex, that is, fatigue at a supraspinal level. In some patients with symptoms of fatigue, the response to TMS after exercise is altered, but the changed MEP behavior is not yet linked to particular symptoms or pathology. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 18–29, 2001
Muscle Fatigue
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Studies of use-dependent changes in neural activation have recently focused on the primary motor cortex. To detect the excitability changes in the primary motor cortex after practice in human subjects, motor-evoked potentials by transcranial magnetic stimulation during motor imagery after just 10 sessions of simple index finger abduction were examined. The present results indicate that width of the output map and amplitudes of motor-evoked potential became progressively larger until practice ended. These flexible short-term modulations of human primary motor cortex seem important and could lead to structural changes in the intracortical networks as the skill becomes more learned and automatic, i.e., ‘adaptation’ as one of the neural mechanisms related to motor learning.
Motor Learning
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Silent period
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Measurements of motor cortex inhibition and excitability can provide useful insights when assessing pathological damage as well as neuronal recovery from injuries. PURPOSE: The aim of this study was to determine the reliability of single pulse transcranial magnetic stimulation (TMS) measures in men and women. METHODS: Nine (5 female) healthy college age participants were tested at three time points, each separated by one week. Single pulse TMS was delivered to the contralateral motor cortex of the dominant first dorsal interosseous. Resting motor threshold (RMT) and the peak-to-peak amplitude of motor evoked potentials (MEP) at 120% RMT were used to quantify motor cortex excitability. The duration of the cortical silent period (CSP), evoked at 120% RMT while participants maintained a contraction at 50% of maximum force, was used to quantify motor cortex inhibition. Reliability was assessed with the intraclass correlation coefficient (ICC 2,1). RESULTS: There was no significant difference across time (p=0.82; p=0.83; p=0.70) or between sexes (p=0.83; p=0.68; p=0.36) for RMT, MEP, or CSP, respectively. Also, there was no significant sex by time interaction (p≥0.34) for any of the measures. Reliability across days was strong for RMT (R=0.69), and very strong for MEP (R=0.87) and CSP (R=0.95). CONCLUSIONS: These results support the use of single pulse TMS measurements to reliably assess and track motor cortex physiological function in men and women.
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Studies of use-dependent changes in neural activation have recently focused on the primary motor cortex. To detect the excitability changes in the primary motor cortex after practice in human subjects, motor-evoked potentials by transcranial magnetic stimulation during motor imagery after just 10 sessions of simple index finger abduction were examined. The present results indicate that width of the output map and amplitudes of motor-evoked potential became progressively larger until practice ended. These flexible short-term modulations of human primary motor cortex seem important and could lead to structural changes in the intracortical networks as the skill becomes more learned and automatic, i.e., 'adaptation' as one of the neural mechanisms related to motor learning.
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Objective: Comparative assessment of best conventional with best theta burst repetitive transcranial magnetic stimulation (rTMS) protocols on human motor cortex excitability.
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Hand muscles
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