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Intracortical modulation of cortical-bulbar responses for the masseter muscle

Ortu, Enzo and Deriu, Franca and Suppa, Antonio and Giaconi, Elena and Tolu, Eusebio and Rothwell, John C. (2008) Intracortical modulation of cortical-bulbar responses for the masseter muscle. The Journal of Physiology, Vol. 586 (14), p. 3385-3404. eISSN 1469-7793. Article.

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DOI: 10.1113/jphysiol.2008.153288

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Abstract

Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the masseter muscles of 12 subjects and the cortical silent period (SP) in nine subjects. Motor evoked potentials (MEPs) were recorded from contralateral (cMM) and ipsilateral (iMM) masseters, activated at 10% of maximal voluntary contraction (MVC). Interstimulus intervals (ISIs) were 2 and 3 ms for SICI, 10 and 15 ms for ICF. TMS of the left masseteric cortex induced MEPs that were larger in the cMM than the iMM; stimulation of right masseteric cortex produced a similar asymmetry in response amplitude. SICI was only observed using a CS intensity of 70% AMT and was equal in both cMM and iMM. SICI was stronger at higher TS intensities, was abolished by muscle activation greater than 10% MVC, and was unaffected by coil orientation changes. Control experiments confirmed that SICI was not contaminated by any inhibitory peripheral reflexes. However, ICF could not be obtained because it was masked by bilateral reflex depression of masseter EMG caused by auditory input from the coil discharge. The SP was bilateral and symmetric; its duration ranged from 35 to 70 ms depending on TS intensity and coil orientation. We conclude that SICI is present in the cortical representation of masseter muscles. The similarity of SICI in cMM and iMM suggests either that a single pool of inhibitory interneurons controls ipsi- and contralateral corticotrigeminal projections or that inhibition is directed to bilaterally projecting corticotrigeminal fibres. Finally, the corticotrigeminal projection seems to be weakly influenced by inhibitory interneurons mediating the cortical SP.

Item Type:Article
ID Code:618
Status:Published
Refereed:Yes
Uncontrolled Keywords:Masseter muscle, motor cortex
Subjects:Area 05 - Scienze biologiche > BIO/09 Fisiologia
Divisions:001 Università di Sassari > 01 Dipartimenti > Scienze biomediche
Publisher:Blackwell / Wiley [?]
eISSN:1469-7793
Copyright Holders:© 2008 The Authors, Journal compilation © 2008 The Physiological Society
Deposited On:18 Aug 2009 10:02

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