title: Minimal Heating at the Skin Surface During Transcranial Direct Current Stimulation.
abstract: OBJECTIVE
  To assess if transcranial direct current stimulation (tDCS) produces a temperature change at the skin surface, if any change is stimulation polarity (anode or cathode) specific, and the contribution of passive heating (joule heat) or blood flow on such change.
  
  
  METHODS
  Temperature differences (ΔTs) in an agar phantom study and an in vivo study (forearm stimulation) including 20 volunteers with both experimental measures and finite element method (FEM) multiphysics prediction (current flow and bioheat) models of skin comprising three tissue layers (epidermis, dermis, and subcutaneous layer with blood perfusion) or of the phantom for active stimulation and control cases were compared. Temperature was measured during pre, post, and stimulation phases for both phantom and subject's forearms using thermocouples.
  
  
  RESULTS
  In the phantom, ΔT under both anode and cathode, compared to control, was not significantly different and less than 0.1°C. Stimulation of subjects resulted in a gradual increase in temperature under both anode and cathode electrodes, compared to control (at t = 20 min: ΔTanode = 0.9°C, ΔTcathode = 1.1°C, ΔTcontrol = 0.05°C). The FEM phantom model predicted comparable maximum ΔT of 0.27°C and 0.28°C (at t = 20 min) for the control and anode/cathode cases, respectively. The FEM skin model predicted a maximum ΔT at t = 20 min of 0.98°C for control and 1.36°C under anode/cathode electrodes.
  
  
  CONCLUSIONS
  Taken together, our results indicate a moderate and nonhazardous increase in temperature at the skin surface during 2 mA tDCS that is independent of polarity, and results from stimulation induced blood flow rather than joule heat.
authors.affiliation: Department of Biomedical Engineering, The City College of New York, CUNY, New York, NY, USA.
authors.forename: Niranjan
authors.initials: N
authors.lastname: Khadka
authors.affiliation: Department of Biomedical Engineering, The City College of New York, CUNY, New York, NY, USA.
authors.forename: Adantchede L
authors.initials: AL
authors.lastname: Zannou
authors.affiliation: Department of Biomedical Engineering, The City College of New York, CUNY, New York, NY, USA.
authors.forename: Fatima
authors.initials: F
authors.lastname: Zunara
authors.affiliation: Department of Biomedical Engineering, The City College of New York, CUNY, New York, NY, USA.
authors.forename: Dennis Q
authors.initials: DQ
authors.lastname: Truong
authors.affiliation: Department of Biomedical Engineering, The City College of New York, CUNY, New York, NY, USA.
authors.forename: Jacek
authors.initials: J
authors.lastname: Dmochowski
authors.affiliation: Department of Biomedical Engineering, The City College of New York, CUNY, New York, NY, USA.
authors.forename: Marom
authors.initials: M
authors.lastname: Bikson
mesh_terms: D000328:Adult; D003198:Computer Simulation; D005260:Female; D064368:Healthy Volunteers; D006361:Heating; D006801:Humans; D008297:Male; D012867:Skin; D012881:Skin Temperature / Q000502:physiology*; D018709:Statistics, Nonparametric; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
keywords: bioheat; erythema; finite element method; flare; passive heating (joule heat); skin; temperature; transcranial direct current stimulation