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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].

The procedure

Patients sit in a comfortable chair or lay down. Two water-soaked electrodes are applied to the patient’s scalp. tDCS requires no sedation. Most patients do not experience side effects. In a small number of cases, however, there is transient headache and fatigue. The treatment is not associated with cognitive or memory loss. Rather, it has been associated with an improvement in cognitive function and working memory which the psychiatric illness may have negatively affected.[2]

Theory and practice

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.[3] 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.[4] Finally recent data demonstrate that tDCS can modulate the function of the spinal cord and of the cerebellum.

A new technology, High-Definition tDCS (HD-tDCS), is currently being developed for the restoration of CNS and PNS function. The advantage of HD-tDCS over conventional big pad tDCS involves using an array of <12 mm diameter stimulation electrodes, that will facilitate focal, safe and customized neuromodulation of the brain function. [5] [6]

See also

References

  1. ^ Bijal Trivedi (April 15, 2006). "Electrify Your Mind - Literally". New Scientist. pp. 34–37.
  2. ^ Transcranial Direct Current Stimulation, Douglas Mental Health University Institute
  3. ^ M. A. Nitsche & W. Paulus (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:10.1111/j.1469-7793.2000.t01-1-00633.x. PMC 2270099. PMID 10990547. {{cite journal}}: Unknown parameter |month= ignored (help)
  4. ^ "Search of: tdcs". ClinicalTrials.gov.
  5. ^ A. Datta; et al. (2009). "Gyri -precise head model of transcranial DC stimulation: Improved spatial focality using a ring electrode versus conventional rectangular pad = [[Brain Stimulation]]". Brain stimulation. 2 Part 4 (4): 201–207. doi:10.1016/j.brs.2009.03.005. PMC 2790295. PMID 20161455. {{cite journal}}: Explicit use of et al. in: |author= (help); URL–wikilink conflict (help); Unknown parameter |month= ignored (help)
  6. ^ P. Minhas; et al. (2010). "Electrodes for high-definition transcuataneous DC stimulation for applications in drug-delivery and electrotherapy, including tDCS". The Journal of Neuroscience Methods. Article in Press (2): 188–97. doi:10.1016/j.jneumeth.2010.05.007. PMC 2920288. PMID 20488204. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)

Further reading

  • Bogdanov OV, Pinchuk DYu, Pisar'kova EV, Shelyakin AM, Sirbiladze KT. The use of the method of transcranial micropolarization to decrease the severity hyperkineses in patients with infantile cerebral palsy. Neurosci. Behav. Physiol. 1994 Sep-Oct;24(5):442-5.
  • 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.


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