Elsevier

Brain Stimulation

Volume 1, Issue 3, July 2008, Pages 206-223
Brain Stimulation

Original Research
Transcranial direct current stimulation: State of the art 2008

https://doi.org/10.1016/j.brs.2008.06.004Get rights and content

Summary

Effects of weak electrical currents on brain and neuronal function were first described decades ago. Recently, DC polarization of the brain was reintroduced as a noninvasive technique to alter cortical activity in humans. Beyond this, transcranial direct current stimulation (tDCS) of different cortical areas has been shown, in various studies, to result in modifications of perceptual, cognitive, and behavioral functions. Moreover, preliminary data suggest that it can induce beneficial effects in brain disorders. Brain stimulation with weak direct currents is a promising tool in human neuroscience and neurobehavioral research. To facilitate and standardize future tDCS studies, we offer this overview of the state of the art for tDCS.

Section snippets

Physical parameters and practical application of tDCS

tDCS differs qualitatively from other brain stimulation techniques such as transcranial electrical stimulation (TES) and transcranial magnetic stimuation (TMS) by not inducing neuronal action potentials because static fields in this range do not yield the rapid depolarization required to produce action potentials in neural membranes. Hence, tDCS might be considered a neuromodulatory intervention. The exposed tissue is polarized and tDCS modifies spontaneous neuronal excitability and activity by

Time course of tDCS-induced modulations of cortical excitability

In the primary motor cortex, the dependence of the efficacy of tDCS from current density and stimulation duration has been systematically explored. Increasing current density or stimulation duration, holding the other parameter constant, results in longer-lasting and stronger effects.13, 14, 15 For increased current density, however, this might not be a linear relationship in each case, because larger current densities will increase the depth of the electrical field relevantly and thus alter

Safety of tDCS

Although tDCS differs in many aspects from pulsed electrical stimulation, for example, a much lower current density is applied, the stimulation does not produce time-locked neuronal firing, and thus comparability between the different methods of stimulation is limited. Studies with pulsed electrical stimulation have identified some possible sources of tissue damage, whose relevance for tDCS will now be discussed.

Generation of electrochemically produced toxins and electrode dissolution products

Conclusions

tDCS has been reintroduced as a noninvasive tool to guide neuroplasticity and modulate cortical function by tonic stimulation with weak direct currents. The aim of this article is to propose guidelines on how to perform tDCS safely and effectively. Because many laboratories have just started using this technique, it is necessary to stratify stimulation protocols to enhance comparability of research results. However, it is also important to underscore that tDCS research is in its early stages

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