Transcranial direct current stimulation
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Transcranial direct current stimulation (tDCS) is the application of weak electrical currents (1-2 mA) to modulate the activity of neurons in the brain.[1]. 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.
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. Priori et al in 1998 at the University of Rome, provided the first demonstration that weak direct current delivered over the scalp during their flow can influence the excitability of the underlying cerebral cortex. In 2000, Michael A. Nitsche and colleagues at the University of Göttingen claimed expanded the findings of Priori et al by demonstrating that anodal polarization of the motor cortex increased the motor response of transcranial magnetic stimulation of the same area even after the current offset; reduction of this response was observed with cathodal polarization. Moreover, these effects were reported to last for an appreciable amount of time after exposure.[2] 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.[3]
Finally recent data demonstrate that tDCS can modulate the funztion of the spinal cord and of the cerebellum.
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[edit] See also
- Cranial electrotherapy stimulation (CES)
- Transcranial magnetic stimulation
- Trancranial alternating-current stimulation
[edit] References
- ^ Bijal Trivedi (April 15, 2006). "Electrify Your Mind - Literally". New Scientist. pp. 34–37. http://www.newscientist.com/article/mg19025471.100.
- ^ M. A. Nitsche & W. Paulus (September 2000). "Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation". The Journal of Physiology 527 Part 3: 633–639. doi:. PMID 10990547. http://jp.physoc.org/cgi/content/full/527/3/633.
- ^ "Search of: tdcs". ClinicalTrials.gov. http://www.clinicaltrials.gov/ct/search?term=tdcs&submit=Search.
[edit] Further reading
- Cogiamanian et al. Effect of spinal transcutaneous direct current stimulation on somatosensory evoked potentials in humans. Clin Neurophysiol 2008; 119: 2636-2640
- Miranda PC, Lomarev M, Hallett M.Modeling the current distribution during transcranial direct current stimulation. Clin Neurophysiol. 2006 Jul;117(7):1623-9.
- Priori A, Berardelli A, Rona S, Accornero N, Manfredi M. Polarization of the human motor cortex through the scalp. Neuroreport 1998;9: 2257–60.
- 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.
[edit] External links
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