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.
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.
Please note that this methodology is only used for research purposes at this time.