Transcranial direct current stimulation (tDCS) is a noninvasive, low-cost and easy-to-use technique that can be applied to modify cerebral excitability. This is achieved by weak direct currents to shift the resting potential of cortical neurons. These currents are applied by attaching two electrodes (usually one anode and one cathode) to distinct areas of the skull. Galvanic Vestibular Stimulation (GVS) is a variant of tDCS where the electrodes are attached to the mastoids behind the ears in order to stimulate the vestibular system. tDCS and GVS are safe when standard procedures are used. We describe the basic physiological mechanisms and application of these procedures. We also review current data on the effects of tDCS and GVS in healthy subjects as well as clinical populations. Significant effects of such stimulation have been reported for motor, visual, somatosensory, attentional, vestibular and cognitive/emotional function as well as for a range of neurological and psychiatric disorders. Moreover, both techniques may induce neuroplastic changes which make them promising techniques in the field of neurorehabilitation. A number of open research questions that could be addressed with tDCS or GVS are formulated in the domains of sensory and motor processing, spatial and nonspatial attention including neglect, spatial cognition and body cognition disorders, as well as novel treatments for various neuropsychological disorders. We conclude that the literature suggests that tDCS and GVS are exciting and easily applicable research tools for neuropsychological as well as clinical-therapeutic investigations.
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