http://www.ox.ac.uk/media/science_blog/brainboosting.html

TDCS uses electrodes placed on the outside of the head to pass tiny currents across regions of the brain for 20 minutes or so. The currents of 1–2 mA make it easier for neurons in these brain regions to fire….

…Critically, this is not just helping to restore function in those with impaired abilities. TDCS can be used to enhance healthy people’s mental capacities. Indeed, most of the research so far has been carried out in healthy adults