title: Corticospinal and transcallosal modulation of unilateral and bilateral contractions of lower limbs.
abstract: OBJECTIVE
  Interhemispheric inhibition may play a role in the expression of bilateral deficit in force (BLD). This study investigated whether the degree of BLD is reflected in the nature of interhemispheric interaction during unilateral and bilateral contractions.
  
  
  METHODS
  Subjects divided into three groups, 'bilateral' (n = 7), 'unilateral' (n = 5) and 'control' (n = 8), performed unilateral and bilateral maximal voluntary isometric knee extensions while receiving electrical stimulation, and transcranial magnetic stimulation of the target and ipsilateral muscles. Main variables of interest included peak force for subsequent calculation of bilateral index, voluntary activation level (VAL), motor evoked potential amplitudes (MEPs) and silent period durations (SPs).
  
  
  RESULTS
  BLD was noted only for the whole sample (p = 0.009), but not for any of the groups. VAL was significantly higher during bilateral compared to unilateral contractions (~97 vs. 92 %, p = 0.023), with no differences between groups. MEPs of target and ipsilateral muscles were significantly bigger during bilateral contractions (p = 0.042 and p = 0.022, respectively), with no differences between groups. No differences in SPs were observed.
  
  
  CONCLUSIONS
  Higher values of MEPs and VAL during bilateral contractions, in conjunction with unaltered SPs, do not support the concept of inhibition related to BLD, but rather suggest the possibility of cortical facilitation. Based on the existing literature, this behavior may be specific to the lower limb musculature, but the possibility of sub-cortical or higher-order neural alterations cannot be excluded.
authors.affiliation: Neuromuscular Research Centre, Department of Biology of Physical Activity, University of Jyväskylä, PL 35, 40014, Jyväskylä, Finland. jakob.skarabot@gmail.com.
authors.forename: Jakob
authors.identifier: http://orcid.org/0000-0002-0118-1216
authors.initials: J
authors.lastname: Škarabot
authors.affiliation: Department of Neurology, University Medical Centre Ljubljana, Zaloška cesta 2, 1000, Ljubljana, Slovenia.
authors.forename: Ruben Perellón
authors.initials: RP
authors.lastname: Alfonso
authors.affiliation: Neuromuscular Research Centre, Department of Biology of Physical Activity, University of Jyväskylä, PL 35, 40014, Jyväskylä, Finland.
authors.forename: Neil
authors.initials: N
authors.lastname: Cronin
authors.affiliation: Department of Neurology, University Medical Centre Ljubljana, Zaloška cesta 2, 1000, Ljubljana, Slovenia.
authors.forename: Jure
authors.initials: J
authors.lastname: Bon
authors.affiliation: Laboratory of Kinesiology, Faculty of Sport, University of Ljubljana, Gortanova ulica 22, 1000, Ljubljana, Slovenia.
authors.forename: Vojko
authors.initials: V
authors.lastname: Strojnik
authors.affiliation: Neuromuscular Research Centre, Department of Biology of Physical Activity, University of Jyväskylä, PL 35, 40014, Jyväskylä, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Avela
mesh_terms: D003337:Corpus Callosum / Q000502:physiology*; D000071080:Cortical Excitability / Q000502:physiology; D004292:Dominance, Cerebral / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D055815:Young Adult
keywords: Bilateral deficit; Corticospinal excitability; Inter-limb; Interhemispheric inhibition; Motor control; TMS; Transcallosal modulation