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Influence of Voluntary Contraction Level, Test Stimulus Intensity and Normalization Procedures on the Evaluation of Short-Interval Intracortical Inhibition

1
INSERM UMR1093-CAPS, Université Bourgogne Franche-Comté, UFR des Sciences du Sport, F-21078 Dijon, France
2
EA4660-C3S Laboratory—Culture, Sport, Health and Society, Université Bourgogne Franche-Comté, 25000 Besançon, France
*
Author to whom correspondence should be addressed.
Brain Sci. 2020, 10(7), 433; https://doi.org/10.3390/brainsci10070433
Received: 27 May 2020 / Revised: 2 July 2020 / Accepted: 6 July 2020 / Published: 8 July 2020
Short-interval intracortical inhibition (SICI) represents an inhibitory phenomenon acting at the cortical level. However, SICI estimation is based on the amplitude of a motor-evoked potential (MEP), which depends on the discharge of spinal motoneurones and the generation of compound muscle action potential (M-wave). In this study, we underpin the importance of taking into account the proportion of spinal motoneurones that are activated or not when investigating the SICI of the right flexor carpi radialis (normalization with maximal M-wave (Mmax) and MEPtest, respectively), in 15 healthy subjects. We probed SICI changes according to various MEPtest amplitudes that were modulated actively (four levels of muscle contraction: rest, 10%, 20% and 30% of maximal voluntary contraction (MVC)) and passively (two intensities of test transcranial magnetic stimulation (TMS): 120 and 130% of motor thresholds). When normalized to MEPtest, SICI remained unchanged by stimulation intensity and only decreased at 30% of MVC when compared with rest. However, when normalized to Mmax, we provided the first evidence of a strong individual relationship between SICI and MEPtest, which was ultimately independent from experimental conditions (muscle states and TMS intensities). Under similar experimental conditions, it is thus possible to predict SICI individually from a specific level of corticospinal excitability in healthy subjects. View Full-Text
Keywords: SICI; muscle contraction; transcranial magnetic stimulation; corticospinal excitability SICI; muscle contraction; transcranial magnetic stimulation; corticospinal excitability
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Neige, C.; Grosprêtre, S.; Martin, A.; Lebon, F. Influence of Voluntary Contraction Level, Test Stimulus Intensity and Normalization Procedures on the Evaluation of Short-Interval Intracortical Inhibition. Brain Sci. 2020, 10, 433.

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