Transcranial direct current stimulation

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Transcranial direct current stimulation (tDCS) is the application of very 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.

The technique has been applied to humans in various forms, probably for centuries. However, in the 1960s a few reasonably well-controlled experiments showed that electrodes placed on the forehead were able to produce noticeable psychological changes that were dependent on the direction of the field. Recently, it was shown by Nitsche and colleagues at the University of Göttingen, that anodal polarization of the motor cortex increased the motor response of transcranial magnetic stimulation of the same area and reduction of this response was observed with cathodal polarization. Moreover, these effects were observed to last for an appreciable amount of time after exposure. Investigators are currently testing its effects 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 amp 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.[1]