title: Methods for extra-low voltage transcranial direct current stimulation: current and time dependent impedance decreases.
abstract: OBJECTIVE
  Though tDCS is well tolerated, it is desirable to further limit the voltage applied for additional safety factors and optimized device design. We investigated the minimum voltage required for tDCS using 1.5 and 2.5mA.
  
  
  METHODS
  Impedance data has been collected prior to, during and after 18 tDCS sessions, using 1.5mA and 2.5mA tDCS currents and three different test current magnitudes. Data was pooled and tested for differences using t-tests, corrected for multiple comparisons. Average impedance data was fitted into a RLC circuit model with additional double integrator.
  
  
  RESULTS
  We report that the impedance drop during tDCS initiation significantly reduces the voltage compliance required to achieve the target current (14.5V for 1.5mA, 18.5V for 2.5mA). Data was well approximated by a 4th order linear impedance model.
  
  
  CONCLUSIONS
  In addition to indicating the feasibility of reduced voltage tDCS, we propose an extra-low voltage "Limited Total Energy" approach where stimulation is continued at voltage compliance allowing time for impedance to decrease and target current to be reached.
  
  
  CONCLUSIONS
  Reduced-voltage and Limited Total Energy tDCS are viable approaches towards more protective and robust tDCS protocols.
authors.affiliation: Department of Biomedical Engineering, The City College of New York of CUNY, New York, NY, United States.
authors.forename: Christoph
authors.initials: C
authors.lastname: Hahn
authors.forename: Justin
authors.initials: J
authors.lastname: Rice
authors.forename: Shiraz
authors.initials: S
authors.lastname: Macuff
authors.forename: Preet
authors.initials: P
authors.lastname: Minhas
authors.forename: Asif
authors.initials: A
authors.lastname: Rahman
authors.forename: Marom
authors.initials: M
authors.lastname: Bikson
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D017097:Electric Impedance; D004558:Electric Stimulation / Q000379:methods*; D004599:Electric Stimulation Therapy / Q000379:methods*; D006801:Humans