title: Effects of volitional contraction on intracortical inhibition and facilitation in the human motor cortex.
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.
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, UK.
authors.forename: Enzo
authors.initials: E
authors.lastname: Ortu
authors.forename: Franca
authors.initials: F
authors.lastname: Deriu
authors.forename: Antonio
authors.initials: A
authors.lastname: Suppa
authors.forename: Eusebio
authors.initials: E
authors.lastname: Tolu
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*
references.citation: J Physiol. 1995 Sep 1;487 ( Pt 2):541-8
references.pmid: 8558482
references.citation: Exp Brain Res. 2003 Aug;151(3):330-7
references.pmid: 12802553
references.citation: Electroencephalogr Clin Neurophysiol. 1998 Oct;109(5):397-401
references.pmid: 9851296
references.citation: Ann Neurol. 1996 Sep;40(3):367-78
references.pmid: 8797526
references.citation: J Physiol. 2003 Aug 1;550(Pt 3):933-46
references.pmid: 12807989
references.citation: J Physiol. 2002 Nov 15;545(1):153-67
references.pmid: 12433957
references.citation: Lancet Neurol. 2003 Mar;2(3):145-56
references.pmid: 12849236
references.citation: Exp Brain Res. 2000 Dec;135(3):293-9
references.pmid: 11146807
references.citation: Clin Neurophysiol. 2000 May;111(5):794-9
references.pmid: 10802448
references.citation: Exp Brain Res. 2003 Aug;151(4):427-34
references.pmid: 12830341
references.citation: Electroencephalogr Clin Neurophysiol. 1998 Aug;109(4):321-30
references.pmid: 9751295
references.citation: Clin Neurophysiol. 2007 Aug;118(8):1785-93
references.pmid: 17574911
references.citation: J Physiol. 1993 Nov;471:501-19
references.pmid: 8120818
references.citation: Exp Brain Res. 1999 Jun;126(4):536-44
references.pmid: 10422717
references.citation: Clin Neurophysiol. 2003 Dec;114(12):2362-9
references.pmid: 14652096
references.citation: Electroencephalogr Clin Neurophysiol Suppl. 1999;52:97-103
references.pmid: 10590980
references.citation: Neurology. 1999 Sep 11;53(4):730-5
references.pmid: 10489033
references.citation: Exp Brain Res. 2007 Feb;177(2):266-74
references.pmid: 16947062
references.citation: J Physiol. 1996 Nov 1;496 ( Pt 3):873-81
references.pmid: 8930851
references.citation: Electroencephalogr Clin Neurophysiol. 1994 Aug;91(2):79-92
references.pmid: 7519144
references.citation: J Physiol. 1998 Aug 15;511 ( Pt 1):181-90
references.pmid: 9679173
references.citation: J Neurophysiol. 2000 Mar;83(3):1426-34
references.pmid: 10712469
references.citation: Exp Brain Res. 1998 Mar;119(2):265-8
references.pmid: 9535577
references.citation: J Physiol. 1998 Jun 1;509 ( Pt 2):607-18
references.pmid: 9575308
references.citation: J Physiol. 2002 Jan 1;538(Pt 1):253-61
references.pmid: 11773332
references.citation: Muscle Nerve. 1997 May;20(5):570-6
references.pmid: 9140363
references.citation: J Physiol. 1998 Apr 15;508 ( Pt 2):625-33
references.pmid: 9508823
references.citation: Neurology. 1998 Nov;51(5):1320-4
references.pmid: 9818853
references.citation: Electroencephalogr Clin Neurophysiol. 1996 Aug;101(4):263-72
references.pmid: 8761035
references.citation: Exp Brain Res. 1996 Apr;109(1):127-35
references.pmid: 8740215
references.citation: Exp Brain Res. 2002 Mar;143(2):240-8
references.pmid: 11880900
references.citation: J Physiol. 2008 Jul 15;586(14):3385-404
references.pmid: 18499727
references.citation: J Physiol. 2001 Jan 15;530(Pt 2):307-17
references.pmid: 11208978
references.citation: J Physiol. 1997 Feb 1;498 ( Pt 3):817-23
references.pmid: 9051592
references.citation: Neurosci Lett. 1999 Aug 6;270(3):137-40
references.pmid: 10462113
references.citation: Exp Brain Res. 1999 Nov;129(2):317-24
references.pmid: 10591905