A common sensation many users of tDCS feel during a tDCS session is a sense of heating and/or a burning at the area of stimulation. In a study now made freely accessible online, Dr. Marom Bikson’s lab at the City College of New York attempted to elucidate the underlying mechanism behind the apparent heating effect tDCS had on the area of stimulation.
The study utilized twenty volunteers in an in vivo study stimulating the forearms to observe the properties of any heating caused by tDCS. The study also attempted to validate the in vivo results with an FEM model, and an agar phantom. Results showed the average heating on the surface of the skin was upwards of ~1 degree Celsius, with the results from the FEM study corroborating this outcome.
The study concluded that the moderate and non-hazardous increase in temperature at the location of stimulation during the 2 mA tDCS session was independent of the polarity of the electrode, and was very likely caused by increased blood flow to the area induced by the tDCS, and not by passive heating (joule heating).
For more on this study, click the link to the publication below: