This couldn’t possibly be a good idea. On Friday the 13th of September, in an old brick building on 13th Street in Boston’s Charlestown neighborhood, a pair of electrodes was attached to my forehead, one over my brain’s left prefrontal cortex, the other just above my right eye socket. I was about to undergo transcranial direct-current stimulation, or tDCS, an experimental technique for delivering extremely low dose electrical stimulation to the brain. Using less than 1 percent of the electrical energy necessary for electroconvulsive therapy, powered by an ordinary nine-volt battery, tDCS has been shown in hundreds of studies to enhance an astonishing, seemingly implausible variety of intellectual, emotional and movement-related brain functions. And its side effects appear limited to a mild tingling at the site of the electrode, sometimes a slight reddening of the skin, very rarely a headache and certainly no seizures or memory loss. Still, I felt more than a bit apprehensive as I prepared to find out if a little bit of juice could amp up my cognitive reserves and make me, in a word, smarter.