Figure 1.

Assumed neural mechanism of tDCS. (a) Without tDCS, the resting potential of the cell is at −70 mV and an incoming excitatory postsynaptic potential (EPSP) arriving 100 ms after onset of the experiment does not reach the threshold for firing at −50 mV (dashed line). (b) If the neuron is close to an anode, the positive voltage from the anode will raise the resting potential towards a more positive voltage and the same EPSP will exceed the threshold and result in a neural spike. (c) If the neuron is close to a cathode, the negative voltage from the cathode will lower the resting potential towards a more negative voltage and the same EPSP will not exceed the threshold.