The effects of bi-hemispheric M1-M1 transcranial direct current stimulation on primary motor cortex neurophysiology and metabolite concentration

Article type: Research Article

Authors: Tremblay, Sara^{a; b; *} | Lafleur, Louis-Philippe^{a; b} | Proulx, Sébastien^{c; d} | Beaulé, Vincent^{a; b} | Latulipe-Loiselle, Alex^a | Doyon, Julien^c | Marjańska, Małgorzata^e | Théoret, Hugo^{a; b}

Affiliations: [a] Département de psychologie, Université de Montréal, Montréal, Canada | [b] Centre de recherche du Centre Hospitalier Universitaire de l’Hôpital Sainte-Justine, Montréal, Canada | [c] Unité de Neuroimagerie Fonctionnelle, Centre de recherche de l’Institut Universitaire de Gériatrie de Montréal, Canada | [d] McGill University, Montréal, Canada | [e] Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, USA

Correspondence: [*] Corresponding author: Sara Tremblay, Département de Psychologie, Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal, QC, H3C 3J7, Canada. Tel.: +1 514 343 6111/Ext. 0890; Fax: +1 514 343 5787; E-mail: sara.tremblay@umontreal.ca.

Abstract: Purpose: 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. Methods: 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. Results: 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. Conclusion: 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.

Keywords: Magnetic resonance spectroscopy, transcranial direct current stimulation, motor cortex, GABA, glutamate

DOI: 10.3233/RNN-150569

Journal: Restorative Neurology and Neuroscience, vol. 34, no. 4, pp. 587-602, 2016