title: Enhanced motor learning with bilateral transcranial direct current stimulation: Impact of polarity or current flow direction?
abstract: OBJECTIVE
  Bilateral transcranial direct current stimulation (TDCS) is superior to unilateral TDCS when targeting motor learning. This effect could be related to either the current flow direction or additive polarity-specific effects on each hemisphere.
  
  
  METHODS
  This sham-controlled randomized study included fifty right-handed healthy subjects in a parallel-group design who performed an exoskeleton-based motor task of the proximal left arm on three consecutive days. Prior to training, we applied either sham, right anodal (a-TDCS), left cathodal (c-TDCS), concurrent a-TDCS and c-TDCS with two independent current sources and return electrodes (double source (ds)-TDCS) or classical bilateral stimulation (bi-TDCS).
  
  
  RESULTS
  Motor performance improved over time for both unilateral (a-TDCS, c-TDCS) and bilateral (bi-TDCS, ds-TDCS) TDCS montages. However, only the two bilateral paradigms led to an improvement of the final motor performance at the end of the training period as compared to the sham condition. There was no difference between the two bilateral stimulation conditions (bi-TDCS, ds-TDCS).
  
  
  CONCLUSIONS
  Bilateral TDCS is more effective than unilateral stimulation due to its polarity-specific effects on each hemisphere rather than due to its current flow direction.
  
  
  CONCLUSIONS
  This study is the first systematic evaluation of stimulation polarity and current flow direction of bi-hemispheric motor cortex TDCS on motor learning of proximal upper limb muscles.
authors.affiliation: Division of Functional and Restorative Neurosurgery, and Centre for Integrative Neuroscience, Eberhard Karls University Tuebingen, Germany. Electronic address: georgios.naros@med.uni-tuebingen.de.
authors.forename: Georgios
authors.initials: G
authors.lastname: Naros
authors.affiliation: Division of Neurorehabilitation, Eberhard Karls University Tuebingen, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Geyer
authors.affiliation: Division of Neurorehabilitation, Eberhard Karls University Tuebingen, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Koch
authors.affiliation: Division of Neurorehabilitation, Eberhard Karls University Tuebingen, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Mayr
authors.affiliation: Division of Neurorehabilitation, Eberhard Karls University Tuebingen, Germany.
authors.forename: Tabea
authors.initials: T
authors.lastname: Ellinger
authors.affiliation: Division of Functional and Restorative Neurosurgery, and Centre for Integrative Neuroscience, Eberhard Karls University Tuebingen, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Grimm
authors.affiliation: Division of Functional and Restorative Neurosurgery, and Centre for Integrative Neuroscience, Eberhard Karls University Tuebingen, Germany. Electronic address: alireza.gharabaghi@uni-tuebingen.de.
authors.forename: Alireza
authors.initials: A
authors.lastname: Gharabaghi
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007858:Learning / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Current direction; Electrode montage; Hemispheric interaction; Polarity; Proximal upper limb muscles; Robotic rehabilitation; Transcranial direct current stimulation