Current Methods and Approaches of Noninvasive Direct Current–Based Neuromodulation Techniques

Transcranial direct current stimulation (tDCS) intends to achieve membrane depolarization or hyperpolarization in neurons by applying electric current to the scalp. This goal and, possibly, other effects on neuronal and glial physiology and on pathological processes within the central nervous system, can be achieved depending on a variety of physical parameters. In this chapter, we describe available techniques of transcutaneous DC stimulation and the practical issues related to their application. We will look at the different electrode types available, their placement, the importance of size, location, connection of wires, electrode gel and extracephalic return electrodes. The advantages and disadvantages of one- versus multichannel stimulation will be discussed. The intensity of stimulation will cover a range up to 3 mA, the importance of duration of stimulation with the potential to reverse polarity with longer duration and the importance of intervals to prolong after effects are discussed. Furthermore, available techniques for spinal and cerebellar stimulation will be covered in detail. Wherever reasonable, we will outline differences between routine application and research or clinical purposes.