title: Effects of simultaneous bilateral tDCS of the human motor cortex.
abstract: BACKGROUND
  Transcranial direct current stimulation (tDCS) is a noninvasive technique that has been investigated as a therapeutic tool for different neurologic disorders. Neuronal excitability can be modified by application of DC in a polarity-specific manner: anodal tDCS increases excitability, while cathodal tDCS decreases excitability. Previous research has shown that simultaneous bilateral tDCS of the human motor cortex facilitates motor performance in the anodal stimulated hemisphere much more than when the same hemisphere is stimulated using unilateral anodal motor cortex tDCS.
  
  
  OBJECTIVE
  The main purpose of this study was to determine whether simultaneous bilateral tDCS is able to increase cortical excitability in one hemisphere whereas decreasing cortical excitability in the contralateral hemisphere. To test our hypothesis, cortical excitability before and after bilateral motor cortex tDCS was evaluated. Moreover, the effects of bilateral tDCS were compared with those of unilateral motor cortex tDCS.
  
  
  METHODS
  We evaluated cortical excitability in healthy volunteers before and after unilateral or bilateral tDCS using transcranial magnetic stimulation.
  
  
  RESULTS
  We demonstrated that simultaneous application of anodal tDCS over the motor cortex and cathodal tDCS over the contralateral motor cortex induces an increase in cortical excitability on the anodal-stimulated side and a decrease in the cathodal stimulated side. We also used the electrode montage (motor cortex-contralateral orbit) method to compare the bilateral tDCS montage with unilateral tDCS montage. The simultaneous bilateral tDCS induced similar effects to the unilateral montage on the cathode-stimulated side. On the anodal tDCS side, the simultaneous bilateral tDCS seems to be a slightly less robust electrode arrangement compared with the placement of electrodes in the motor cortex-contralateral orbit montage. We also found that intersubject variability of the excitability changes that were induced by the anodal motor cortex tDCS using the bilateral montage was lower than that with the unilateral montage.
  
  
  CONCLUSIONS
  This is the first study in which cortical excitability before and after bilateral motor cortex tDCS was extensively evaluated, and the effects of bilateral tDCS were compared with unilateral motor cortex tDCS. Simultaneous bilateral tDCS seems to be a useful tool to obtain increases in cortical excitability of one hemisphere whereas causing decreases of cortical excitability in the contralateral hemisphere (e.g.,to treat stroke).
authors.affiliation: FENNSI Group, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Mordillo-Mateos
authors.affiliation: Servicio de Neurología, Hospital La Mancha Centro, SESCAM, Alcázar de San Juan, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Turpin-Fenoll
authors.affiliation: Servicio de Neurología, Hospital La Mancha Centro, SESCAM, Alcázar de San Juan, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Millán-Pascual
authors.affiliation: FENNSI Group, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain.
authors.forename: Natalia
authors.initials: N
authors.lastname: Núñez-Pérez
authors.affiliation: FENNSI Group, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain.
authors.forename: Ivan
authors.initials: I
authors.lastname: Panyavin
authors.affiliation: FENNSI Group, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain.
authors.forename: José Maria
authors.initials: JM
authors.lastname: Gómez-Argüelles
authors.affiliation: Servicio de Neurología, Hospital La Mancha Centro, SESCAM, Alcázar de San Juan, Spain.
authors.forename: Enrique
authors.initials: E
authors.lastname: Botia-Paniagua
authors.affiliation: Neurosignals Group, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain.
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Foffani
authors.affiliation: Department of Neurology, Christian-Albrechts University, Kiel, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lang
authors.affiliation: FENNSI Group, Hospital Nacional de Parapléjicos, SESCAM, Toledo, Spain. Electronic address: antonioo@sescam.jccm.es.
authors.forename: Antonio
authors.initials: A
authors.lastname: Oliviero
mesh_terms: D000328:Adult; D004307:Dose-Response Relationship, Radiation; D019054:Evoked Potentials, Motor / Q000502:physiology* / Q000528:radiation effects*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology* / Q000528:radiation effects*; D011829:Radiation Dosage; D050781:Transcranial Magnetic Stimulation / Q000379:methods*