Transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is the application of weak electrical currents (1-2 mA) to modulate the activity of neurons in the brain. Several generations of neurophysiological experiments have shown that neurons respond to static (DC) electrical fields by altering their firing rates. Firing increases when the positive pole or electrode (anode) is located near the cell body or dendrites and decrease when the field is reversed. However, when the electrodes are placed on the scalp, the current density produced in the brain is exceedingly small, changing membrane potentials only by a fraction of a millivolt. It is still under debate whether such small currents can cause noticeable effects.

In the 1960s, a few reasonably well-controlled experiments suggested that electrodes placed on the forehead can produce noticeable psychological changes that were dependent on the direction of the field.In 2000, Michael A. Nitsche and colleagues at the University of Göttingen claimed that anodal polarization of the motor cortex increased the motor response of transcranial magnetic stimulation of the same area; reduction of this response was observed with cathodal polarization.Moreover, these effects were reported to last for an appreciable amount of time after exposure. [Cite journal
author = M. A. Nitsche & W. Paulus
title = Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation
journal = The Journal of Physiology
volume = 527 Part 3
pages = 633–639
year = 2000
month = September
pmid = 10990547
url = http://jp.physoc.org/cgi/content/full/527/3/633] Investigators are currently testing the validity of these claims and the effects of tDCS on other brain areas and functions.

DC brain polarization is not "stimulation" in the same sense as transcranial magnetic stimulation or the stimulation of the brain and nerves with conventional electrical techniques. It does not appear to cause nerve cell firing on its own and does not produce discrete effects such as the muscle twitches associated with classical stimulation. It is also important to distinguish it from electroconvulsive therapy, which is used to treat mental illnesses such as major depression by passing pulses of approximately 1 ampere into the brain in order to provoke an epileptic seizure. Currently tDCS is being studied for the treatment of a number of conditions including major depression. [Cite web
url = http://www.clinicaltrials.gov/ct/search?term=tdcs&submit=Search
title = Search of: tdcs
publisher = ClinicalTrials.gov]

ee also

* Cranial electrotherapy stimulation (CES)
* Transcranial magnetic stimulation

References

* Bijal Trivedi, [http://www.newscientist.com/article/mg19025471.100 "Electrify Your Mind - Literally"] , "New Scientist" April 15, 2006, pp 34-37.
* Miranda PC, Lomarev M, Hallett M.Modeling the current distribution during transcranial direct current stimulation. Clin Neurophysiol. 2006 Jul;117(7):1623-9.
* Wagner T, Fregni F, Fecteau S, Grodzinsky A, Zahn M, Pascual-Leone A. Transcranial direct current stimulation: a computer-based human model study. Neuroimage. 2007 Apr 15;35(3):1113-24.