The feelings experienced during a typical tDCS session can vary from individual to individual, and can be based on several factors such as as the montage (electrode placement) being used, level of current, and length of the session. The most common sensation associated with tDCS is a slight tingling, itching, or “warming” sensation felt at the source of the electrodes. This sensation can often be suppressed by applying additional saline solution, or by applying slight pressure to the sponge electrodes to help saturate the area. Adding additional saline solution usually requires stopping the session and removing the electrodes, however saline can be applied easily and comfortably during a tDCS session by using a saline solution applicator bottle.
In addition the the above, some individuals claim to experience a metallic taste in their mouth, but usually report it to be temporary and only during the start of the session. Sometimes it is possible to experience the appearance of a very flash of white light, however this is very rare and only possible if the device being used does not feature “ramping,” and the electrodes are positioned near the optical nerve (near the eyes). Almost all of the tDCS devices being produced by reputable companies feature this technology. The Brain Stimulator v3.0 features internal current stepping, which another form of ramping technology which results in an incredibly comfortable tDCS session.
Overall, most people describe tDCS as being a relatively positive experience, and some report not feeling anything at all!
For some related information, check out: Are there any side effects associated with tDCS?