title: Modeling the current distribution during transcranial direct current stimulation.
abstract: OBJECTIVE
  To investigate the spatial distribution of the magnitude and direction of the current density in the human head during transcranial direct current stimulation (tDCS).
  
  
  METHODS
  The current density distribution was calculated using a numerical method to implement a standard spherical head model into which current was injected by means of large electrodes. The model was positioned in 'MNI space' to facilitate the interpretation of spatial coordinates.
  
  
  RESULTS
  The magnitude and direction of the current density vector are illustrated in selected brain slices for four different electrode montages. Approximately half of the current injected during tDCS is shunted through the scalp, depending on electrode dimension and position. Using stimulating currents of 2.0 mA, the magnitude of the current density in relevant regions of the brain is of the order of 0.1 A/m2, corresponding to an electric field of 0.22 V/m.
  
  
  CONCLUSIONS
  Calculations based on a spherical model of the head can provide useful information about the magnitude and direction of the current density vector in the brain during tDCS, taking into account the geometry and position of the electrodes. Despite the inherent limitations of the spherical head model, the calculated values are comparable to those used in the most recent in vitro studies on modulation of neuronal activity.
  
  
  CONCLUSIONS
  The methodology presented in this paper may be used to assess the current distribution during tDCS using new electrode montages, to help optimize montages that target a specific region of the brain or to preliminarily investigate compliance with safety guidelines.
authors.affiliation: Faculty of Sciences, Institute of Biophysics and Biomedical Engineering, University of Lisbon, Campo Grande, 1749-016 Lisbon, Portugal. pcmiranda@fc.ul.pt
authors.forename: Pedro Cavaleiro
authors.initials: PC
authors.lastname: Miranda
authors.forename: Mikhail
authors.initials: M
authors.lastname: Lomarev
authors.forename: Mark
authors.initials: M
authors.lastname: Hallett
mesh_terms: D001921:Brain / Q000502:physiology / Q000528:radiation effects*; D001931:Brain Mapping; D004558:Electric Stimulation; D004566:Electrodes; D006801:Humans; D008959:Models, Neurological