Transcranial Direct Current Stimulation (tDCS)
Transcranial direct current stimulation is a non-invasive method that shifts membrane potential towards hypo- or hyperpolarization and therefore leads to functional changes in a discrete area of the cerebral cortex. 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.
Neurophysiological studies have shown that slow changes in cortical scalp potential reflect overall activity of cortical neuronal networks. These scalp potentials reflect shifts in membrane potentials of the cortical neurons. Over the past 7 years tDCS has evolved as an important tool to non-invasively manipulate specific neural circuits of the human brain. Many well-controlled experiments have shown that electrodes placed on the forehead can produce noticeable psychological changes that were dependent on the direction of the field. tDCS has been shown in double-blind clinical research studies to be an effective treatment for migraines, depression and anxiety, among other issues. See our “Scientific Research” section for more details.
It is important not to confuse tDCS with regional transcranial magnetic stimulation (rTMS) or the stimulation of the brain and nerves with conventional electrical techniques. tDCS 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.