Transcranial Electrical Stimulation: Methodology and Applications

Abstract

Low-intensity transcranial current stimulation is a rapidly growing field of research. Transcranial direct current stimulation (tDCS) is the dominant paradigm of this new field, with transcranial alternating current stimulation (tACS) just emerging. Anodal stimulation with tDCS has excitatory effects on the underlying cortex, whereas cathodal stimulation has inhibitory effects. Because both electrodes have significant brain effects when placed at cephalic areas, the term “reference” electrode should be avoided. Most studies have applied tDCS to the motor cortex, the prefrontal cortex, and the occipital cortex. Applications of tDCS include modulation of electrophysiological and hemodynamic brain activity, symptom reduction in neurological and psychiatric pathology, and cognitive improvement in healthy volunteers or clinical populations. There is evidence of motor improvement in patients with stroke, pain reduction in fibromyalgia, improved mood in patients with unipolar or bipolar depression, and reduced craving. Healthy volunteers are shown to improve their verbal fluency, working memory, and implicit learning. Moreover, there are interactions of tDCS with various pharmacological substances. There are no significant side effects, apart from minor skin lesions when tap water is used instead of saline solution in the sponge electrodes. Further research is required to reveal the potential of tACS.

Acknowledgments

Preparation of this article was supported by the HIVE project, a Future and Emerging Technologies (FET) programme within the 7th Framework Programme for Research of the European Commission, under FET Open grant number: 222079 (http://hive-eu.org/). We thank Pedro Cavaleiro Miranda from the University of Lisbon for estimating current density distribution.