Transcranial Direct Current Stimulation (tDCS)
Transcranial direct current stimulation, abbreviated tDCS (Figure 1), is a noninvasive technique that allows interfering with the brain's electrical activity. This technique works differently from the more famous TMS sister, so be aware to not confuse them.
With tDCS, two electrodes (one anode and one cathode) are applied to the subject (either the head only or head and shoulder, depending on your aims). Accordingly to the polarity, different effects can be observed: interference or facilitation. Further, different types of montages can be used: unipolar, bipolar etc.
tDCS can be used in Psychology together with behavioral testing (both on-line, during stimulation, and off-line, after stimulation) to explore the effects of specific central nervous system neurons stimulation on cognitive abilities.
Obviously, I made it simple. If you want to know more details about the procedure and the function of different montages HERE there is a very nice article describing them.
Other useful references on guidelines and risks:
Fregni F., Nitsche M.A, Loo C.K., Brunori A.R., Marangolo P., Leite J., Carvalho S., Bolognini N., et al. (2014) Regulatory considerations for the clinical and research use of transcranial direct current stimulation (tDCS): review and recommendations from an expert planel. Clinical Research and Regulatory Affairs, 1-14.
Nitsche M.A., , Cohen L G., Wassermann E. M., Priori A., Lang N., Antal A., Paulus W.,Hummel F., Boggio P.S., Fregni F., Pascual-Leone A. (2008). Transcranial direct current stimulation: State of the art. Brain Stimulation, 1, 206–23.
Palm U., Keeser D., Schiller C., Fintescu Z., Reisinger E., Padberg F. et al. (2008). Skin lesions after treatment with transcranial direct current stimulation (tDCS). Brain Stimulation, 1, 386-387.
Woods A.J., Antal A., Bikson M., Boggio P.S., Brunori A.R., Celnik P., Cohen L.G., Fregni F., Hermann C.S., Kappenman E.S., Knotkova H., Liebetanz D., Miniussi C., Miranda P.C., Paulus W., Priori A., Reato D., Stagg C., Wenderoth N., Nitsche M.A. (2016). A technical guide to tDCS, and related non-invasive brain stimulation. Clinical Neurophysiology, 127, 1031-1048.
(TCT Research tDCS 1ch stimulator; 2012 TCT Research Limited, Hong Kong)