The notion that low levels of electrical stimulation applied to the scalp, barely enough to create a mild tingling sensation, could activate the brain is a relatively new and somewhat controversial idea. The technique, called transcranial direct current stimulation (tDCS) has been reported to modify mood, emotion, and cognition, yet researchers lack any evidence for how -- or even if -- it directly modulates brain activity. Still, some researchers see its potential for a new strategy to treat psychiatric disorders.