Scientific research findings suggest that tDCS causes polarity-dependent alterations in cortical excitability and activity. In other words, of the two electrodes (the positive Anode & the negative Cathode), Anodal stimulation increases cortical excitability, while Cathodal stimulation decreases cortical excitability. These changes in cortical excitability are most likely initiated through respective depolarization and hyper-polarization of the underlying neurons. It appears that this effect can be attributed to a sub-threshold modulation of resting membrane potential, which can persist even after stimulation. In simpler terms, tDCS does not actually cause neurons to fire, but instead increases the likelihood of them firing, by increasing “neuronal excitability”.