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Intracortical circuits, sensorimotor integration and plasticity in human motor cortical projections to muscles of the lower face

Pilurzi, Giovanna and Hasan, A. and Saifee, T.A. and Tolu, Eusebio and Rothwell, John C. and Deriu, Franca (2013) Intracortical circuits, sensorimotor integration and plasticity in human motor cortical projections to muscles of the lower face. the Journal of physiology, Vol. 591 (7), p. 1889-1906. ISSN 0022-3751. eISSN 1469-7793. Article.

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DOI: 10.1113/jphysiol.2012.245746

Abstract

Previous studies of the cortical control of human facial muscles documented the distribution of corticobulbar projections and the presence of intracortical inhibitory and facilitatory mechanisms. Yet surprisingly, given the importance and precision in control of facial expression, there have been no studies of the afferent modulation of corticobulbar excitability or of the plasticity of synaptic connections in the facial primary motor cortex (face M1). In 25 healthy volunteers, we used standard single- and paired-pulse transcranial magnetic stimulation (TMS) methods to probe motor-evoked potentials (MEPs), short-intracortical inhibition, intracortical facilitation, short-afferent and long-afferent inhibition and paired associative stimulation in relaxed and active depressor anguli oris muscles. Single-pulse TMS evoked bilateral MEPs at rest and during activity that were larger in contralateral muscles, confirming that corticobulbar projection to lower facial muscles is bilateral and asymmetric, with contralateral predominance. Both short-intracortical inhibition and intracortical facilitation were present bilaterally in resting and active conditions. Electrical stimulation of the facial nerve paired with a TMS pulse 5–200 ms later showed no short-afferent inhibition, but long-afferent inhibition was present. Paired associative stimulation tested with an electrical stimulation–TMS interval of 20 ms significantly facilitated MEPs for up to 30 min. The long-term potentiation, evoked for the first time in face M1, demonstrates that excitability of the facial motor cortex is prone to plastic changes after paired associative stimulation. Evaluation of intracortical circuits in both relaxed and active lower facial muscles as well as of plasticity in the facial motor cortex may provide further physiological insight into pathologies affecting the facial motor system.

Item Type:Article
ID Code:9954
Status:Published
Refereed:Yes
Uncontrolled Keywords:Human facial muscles, cortical control, transcranial magnetic stimulation (TMS) methods, motor-evoked potentials (MEPs)
Subjects:Area 05 - Scienze biologiche > BIO/09 Fisiologia
Divisions:001 Università di Sassari > 01-a Nuovi Dipartimenti dal 2012 > Scienze Biomediche
Publisher:Blackwell / Wiley
ISSN:0022-3751
eISSN:1469-7793
Copyright Holders:© 2013 The Authors. The Journal of Physiology C © 2013 The Physiological Society
Deposited On:07 Jul 2014 12:22

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