title: The effects of bi-hemispheric M1-M1 transcranial direct current stimulation on primary motor cortex neurophysiology and metabolite concentration.
abstract: The aim of the present study was to assess, in healthy individuals, the impact of M1-M1 tDCS on primary motor cortex excitability using transcranial magnetic stimulation and sensorimotor metabolite concentration using 1H-MRS.
  
  
  
  For both experiments, each participant received the three following interventions (20 min tDCS, 1 mA): left-anodal/right-cathodal, left-cathodal/right-anodal, sham. The effects of tDCS were assessed via motor evoked potentials (experiment 1) and metabolite concentrations (experiment 2) immediately after and 12 minutes following the end of stimulation and compared to baseline measurement.
  
  
  
  No effect of M1-M1 tDCS on corticospinal excitability was found. Similarly, M1-M1 tDCS did not significantly modulate metabolite concentrations. High inter-subject variability was noted. Response rate analysis showed a tendency towards inhibition following left-anodal/right-cathodal tDCS in 50% of participants and increased GABA levels in 45% of participants.
  
  
  
  In line with recent studies showing important inter-subject variability following M1-supraorbital tDCS, the present data show that M1-M1 stimulation is also associated with large response variability. The absence of significant effects suggests that current measures may lack sensitivity to assess changes in M1 neurophysiology and metabolism associated with M1-M1 tDCS.
authors.affiliation: Département de psychologie, Université de Montréal, Montréal, Canada.|Centre de recherche du Centre Hospitalier Universitaire de l'Hôpital Sainte-Justine, Montréal, Canada.
authors.forename: Sara
authors.initials: S
authors.lastname: Tremblay
authors.affiliation: Département de psychologie, Université de Montréal, Montréal, Canada.|Centre de recherche du Centre Hospitalier Universitaire de l'Hôpital Sainte-Justine, Montréal, Canada.
authors.forename: Louis-Philippe
authors.initials: LP
authors.lastname: Lafleur
authors.affiliation: Unité de Neuroimagerie Fonctionnelle, Centre de recherche de l'Institut Universitaire de Gériatrie de Montréal, Canada.|McGill University, Montréal, Canada.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Proulx
authors.affiliation: Département de psychologie, Université de Montréal, Montréal, Canada.|Centre de recherche du Centre Hospitalier Universitaire de l'Hôpital Sainte-Justine, Montréal, Canada.
authors.forename: Vincent
authors.initials: V
authors.lastname: Beaulé
authors.affiliation: Département de psychologie, Université de Montréal, Montréal, Canada.
authors.forename: Alex
authors.initials: A
authors.lastname: Latulipe-Loiselle
authors.affiliation: Unité de Neuroimagerie Fonctionnelle, Centre de recherche de l'Institut Universitaire de Gériatrie de Montréal, Canada.
authors.forename: Julien
authors.initials: J
authors.lastname: Doyon
authors.affiliation: Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, USA.
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Marjańska
authors.affiliation: Département de psychologie, Université de Montréal, Montréal, Canada.|Centre de recherche du Centre Hospitalier Universitaire de l'Hôpital Sainte-Justine, Montréal, Canada.
authors.forename: Hugo
authors.initials: H
authors.lastname: Théoret
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000000981:diagnostic imaging / Q000378:metabolism / Q000502:physiology*; D066244:Proton Magnetic Resonance Spectroscopy; D011712:Pyramidal Tracts / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid
keywords: GABA; Magnetic resonance spectroscopy; glutamate; motor cortex; transcranial direct current stimulation