Effects of volitional contraction on intracortical inhibition and facilitation in the human motor cortex

Enzo Ortu, Franca Deriu, Antonio Suppa, Eusebio Tolu, John C. Rothwell

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Abstract

Short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were assessed in the cortical motor area of the first dorsal interosseous muscle (FDI) of 16 healthy subjects. Paired-pulse TMS was delivered to the left hemisphere at the following interstimulus intervals (ISIs): 2 and 3 ms for SICI, 10 and 15 ms for ICF and 1-5 ms for SICF. Motor-evoked potentials were recorded from the resting and active right FDI. The effects exerted on SICI and ICF by four intensities (60-90% of active motor threshold, AMT) of the conditioning stimulus (S1) and by three levels of muscle contraction (10%, 25%, 50% of maximal voluntary contraction, MVC) were evaluated. The effects exerted on SICF were evaluated with two intensities (90% and 70% of AMT) of the test stimulus (S2) and with the same levels of muscle contraction. Results showed that: (i) during 10% MVC, maximum SICI was observed with S1 = 70% AMT; (ii) the amount of SICI obtained with S1 = 70% AMT was the same at rest as during 10% MVC, but decreased at higher contraction levels; (iii) ICF was observed only at rest with S1 = 90% AMT; (iv) SICF was facilitated at 10% and 25% MVC, but not at 50% MVC. We conclude that during muscle activation, intracortical excitability reflects a balance between activation of SICI and SICF systems. Part of the reduction in SICI during contraction is due to superimposed recruitment of SICF. Low intensity (70% AMT) conditioning stimuli can test SICI independently of effects on SICF at low contraction levels.

Original languageEnglish
Pages (from-to)5147-5159
Number of pages13
JournalJournal of Physiology
Volume586
Issue number21
DOIs
Publication statusPublished - 2008

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Motor Cortex
Muscle Contraction
Muscles
Motor Evoked Potentials
Healthy Volunteers

ASJC Scopus subject areas

  • Physiology

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Effects of volitional contraction on intracortical inhibition and facilitation in the human motor cortex. / Ortu, Enzo; Deriu, Franca; Suppa, Antonio; Tolu, Eusebio; Rothwell, John C.

In: Journal of Physiology, Vol. 586, No. 21, 2008, p. 5147-5159.

Research output: Contribution to journalArticle

Ortu, Enzo ; Deriu, Franca ; Suppa, Antonio ; Tolu, Eusebio ; Rothwell, John C. / Effects of volitional contraction on intracortical inhibition and facilitation in the human motor cortex. In: Journal of Physiology. 2008 ; Vol. 586, No. 21. pp. 5147-5159.
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abstract = "Short-interval intracortical inhibition (SICI), intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were assessed in the cortical motor area of the first dorsal interosseous muscle (FDI) of 16 healthy subjects. Paired-pulse TMS was delivered to the left hemisphere at the following interstimulus intervals (ISIs): 2 and 3 ms for SICI, 10 and 15 ms for ICF and 1-5 ms for SICF. Motor-evoked potentials were recorded from the resting and active right FDI. The effects exerted on SICI and ICF by four intensities (60-90{\%} of active motor threshold, AMT) of the conditioning stimulus (S1) and by three levels of muscle contraction (10{\%}, 25{\%}, 50{\%} of maximal voluntary contraction, MVC) were evaluated. The effects exerted on SICF were evaluated with two intensities (90{\%} and 70{\%} of AMT) of the test stimulus (S2) and with the same levels of muscle contraction. Results showed that: (i) during 10{\%} MVC, maximum SICI was observed with S1 = 70{\%} AMT; (ii) the amount of SICI obtained with S1 = 70{\%} AMT was the same at rest as during 10{\%} MVC, but decreased at higher contraction levels; (iii) ICF was observed only at rest with S1 = 90{\%} AMT; (iv) SICF was facilitated at 10{\%} and 25{\%} MVC, but not at 50{\%} MVC. We conclude that during muscle activation, intracortical excitability reflects a balance between activation of SICI and SICF systems. Part of the reduction in SICI during contraction is due to superimposed recruitment of SICF. Low intensity (70{\%} AMT) conditioning stimuli can test SICI independently of effects on SICF at low contraction levels.",
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