title: Voluntary activation of ankle muscles is accompanied by subcortical facilitation of their antagonists.
abstract: Flexion and extension movements are organized reciprocally, so that extensor motoneurones in the spinal cord are inhibited when flexor muscles are active and vice versa. During and just prior to dorsiflexion of the ankle, soleus motoneurones are thus inhibited as evidenced by a depression of the soleus H-reflex. It is therefore surprising that soleus motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) have been found not to be reduced and even facilitated during a voluntary dorsiflexion. The objective of this study was to investigate if MEPs, evoked by TMS, show a similar facilitation prior to and at the onset of contraction of muscles that are antagonists to the muscle in which the MEP is evoked and if so, examine the origin of such a facilitatory motor programme. Eleven seated subjects reacted to an auditory cue by contracting either the tibialis anterior (TA) or soleus muscle of the left ankle. TMS was applied to the hotspot of TA and soleus muscles on separate days. Stimuli were delivered prior to and at the beginning of contraction. Soleus MEPs were significantly facilitated when TMS was applied 50 ms prior to onset of plantar flexion. Surprisingly, soleus MEPs were also facilitated (although to a lesser extent) at a similar time in relation to the onset of dorsiflexion. TA MEPs were facilitated 50 ms prior to onset of dorsiflexion and neither depressed nor facilitated prior to plantar flexion. No difference was found between the facilitation of the soleus MEP and motor evoked responses to cervicomedullary stimulation prior to dorsiflexion, suggesting that the increased soleus MEPs were not caused by changes at a cortical level. This was confirmed by the observation that short-latency facilitation of the soleus H-reflex by subthreshold TMS was increased prior to plantar flexion, but not prior to dorsiflexion. These findings suggest that voluntary contraction at the ankle is accompanied by preceding facilitation of antagonists by a subcortical motor programme. This may help to ensure that the direction of movement may be changed quickly and efficiently during functional motor tasks.
authors.affiliation: Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark. ssgeertsen@ifi.ku.dk
authors.forename: Svend S
authors.initials: SS
authors.lastname: Geertsen
authors.forename: Abraham T
authors.initials: AT
authors.lastname: Zuur
authors.forename: Jens B
authors.initials: JB
authors.lastname: Nielsen
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000842:Ankle / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D003463:Cues; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
references.citation: J Physiol. 1993 May;464:575-93
references.pmid: 8229819
references.citation: Clin Neurophysiol. 2000 Jun;111(6):1008-14
references.pmid: 10825707
references.citation: Exp Brain Res. 2001 Aug;139(4):391-7
references.pmid: 11534862
references.citation: J Physiol. 2000 Nov 1;528(Pt 3):633-45
references.pmid: 11060136
references.citation: Exp Brain Res. 2006 Mar;169(3):427-32
references.pmid: 16273394
references.citation: J Physiol. 2008 Sep 1;586(17):4091-105
references.pmid: 18599540
references.citation: J Physiol. 1976 Jun;258(2):467-87
references.pmid: 822152
references.citation: J Physiol. 1993 Nov;471:223-43
references.pmid: 8120805
references.citation: J Physiol. 1991 Jan;432:381-99
references.pmid: 1886060
references.citation: J Physiol. 1992 Sep;455:425-46
references.pmid: 1336554
references.citation: Acta Physiol Scand. 1994 Nov;152(3):341-3
references.pmid: 7872011
references.citation: Muscle Nerve. 1999 Jul;22(7):857-63
references.pmid: 10398202
references.citation: J Physiol. 1995 May 1;484 ( Pt 3):777-89
references.pmid: 7623292
references.citation: Ann Neurol. 1991 Apr;29(4):418-27
references.pmid: 1929211
references.citation: J Neurophysiol. 1999 Jan;81(1):129-39
references.pmid: 9914274
references.citation: J Physiol. 1999 Oct 15;520 Pt 2:605-19
references.pmid: 10523426
references.citation: Can J Neurol Sci. 1995 Feb;22(1):36-42
references.pmid: 7750071
references.citation: J Neurophysiol. 1996 May;75(5):1826-42
references.pmid: 8734583
references.citation: J Physiol. 1987 Aug;389:163-85
references.pmid: 3681725
references.citation: Mov Disord. 2002;17 Suppl 2:S27-9
references.pmid: 11836749
references.citation: Exp Brain Res. 2008 Jun;187(4):497-507
references.pmid: 18458890
references.citation: Ciba Found Symp. 1987;132:98-117
references.pmid: 3123173
references.citation: J Neurophysiol. 1987 Jan;57(1):56-71
references.pmid: 3559681
references.citation: Suppl Clin Neurophysiol. 2004;57:554-62
references.pmid: 16106656
references.citation: J Appl Physiol (1985). 2008 Sep;105(3):915-22
references.pmid: 18583382
references.citation: J Neurophysiol. 2003 Nov;90(5):3168-77
references.pmid: 12878714
references.citation: Acta Physiol Scand. 1994 Dec;152(4):351-63
references.pmid: 7701936
references.citation: Electroencephalogr Clin Neurophysiol. 1994 Dec;93(6):421-7
references.pmid: 7529691
references.citation: J Physiol. 1989 Sep;416:255-72
references.pmid: 2607451
references.citation: Exp Brain Res. 1990;81(1):35-45
references.pmid: 2394229
references.citation: J Neurophysiol. 2005 Aug;94(2):934-42
references.pmid: 15800077
references.citation: Electroencephalogr Clin Neurophysiol. 1995 Dec;97(6):416-23
references.pmid: 8536594
references.citation: J Physiol. 1984 Apr;349:249-72
references.pmid: 6737294
references.citation: Exp Brain Res. 2006 Nov;175(3):526-35
references.pmid: 16924489
references.citation: J Physiol. 2002 Jun 15;541(Pt 3):949-58
references.pmid: 12068053
references.citation: J Neurosci. 1982 Jun;2(6):791-805
references.pmid: 7086484
references.citation: J Physiol. 1995 Aug 1;486 ( Pt 3):779-88
references.pmid: 7473238
references.citation: J Physiol. 2002 Mar 15;539(Pt 3):903-11
references.pmid: 11897859
references.citation: J Neurosci Methods. 1997 Jun 27;74(2):201-18
references.pmid: 9219889
references.citation: J Neurophysiol. 1982 Feb;47(2):287-302
references.pmid: 7062101
references.citation: Acta Physiol Scand. 1972 May;85(1):136-8
references.pmid: 4340652
references.citation: J Physiol. 1994 May 15;477(Pt 1):47-58
references.pmid: 8071888
references.citation: Exp Brain Res. 2003 Jan;148(2):261-5
references.pmid: 12520416
references.citation: Nature. 1999 Oct 7;401(6753):590-4
references.pmid: 10524626