Transcranial direct current stimulation - A new tool for human cognitive neuroscience

Transcranial direct current stimulation (tDCS) is a non-invasive procedure of cortical stimulation, in which weak direct currents are used to polarize target brain regions. Depending on the polarity of the stimulation, tDCS can increase (anodal tDCS) or decrease (cathodal tDCS) cortical excitability in the stimulated brain regions and thereby enable the investigation of the causal relationships between brain activity and behavior. Recently, tDCS has been increasingly used to investigate human cognitive and motor functions in both healthy volunteers and neurological patients. Although tDCS generally produces diffuse cortical stimulation over a period of time, it has several advantages over other brain-stimulation tools such as transcranial magnetic stimulation (TMS). First, since tDCS produces less artifacts such as acoustic noise and muscle twitching, it is more suitable for double-blind, sham-controlled studies and clinical applications. Second, tDCS is not very expensive and can be performed with compact equipment, it can be easily combined with ongoing projects in neuroscience and psychology laboratories. Third, the facilitation of motor and cognitive functions by anodal tDCS may have great potential for cognitive and motor enhancement, for example, to support learning in healthy volunteers and to expedite the rehabilitation process in neurological patients. Finally, thus far, seizure incidents have not been reported in tDCS studies. tDCS has thus become a complementary tool to TMS and occupies a unique position in current cognitive neuroscience.