Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation

1. In this paper we demonstrate in the intact human the possibility of a no n-invasive modulation of motor cortex excitability by the application of we ak direct current through the scalp. 2. Excitability changes of up to 40%, revealed by transcranial magnetic sti mulation, were accomplished and lasted for several minutes after the end of current stimulation. 3. Excitation could be achieved selectively by anodal stimulation, and inhi bition by cathodal stimulation. 4. By varying the current intensity and duration, the strength and duration of the after-effects could be controlled. 5. The effects were probably induced by modification of membrane polarisati on. Functional alterations related to post-tetanic potentiation, short-term potentiation and processes similar to postexcitatory central inhibition ar e the likely candidates for the excitability changes after the end of stimu lation. Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive, painl ess, reversible, selective and focal way.