What if there was a secret world where people--among them US soldiers and Silicon Valley wunderkinds--were making themselves smarter? Their reaction times, aptitude for language, problem-solving skills, and marksmanship are all improving under the watchful eye of scientists and DARPA (the defense advanced research projects agency). Such are the claims of transcranial direct current stimulation--also known as TDCS--a noninvasive treatment where you strap electrodes to your skull to zap your brain. It all sounds like a shady society of secret humans snatched from the pages of comic books, but it's not. It's real life. And Mary H. K. Choi visits as a human guinea pig to conduct experiments on herself to see what she'll find out, to hilarious and fascinating results. Mary H. K. Choi has written for GQ, The New York Times, New York, Wired, and Glamour. She is the former editor of MTV Style and executive producer of the documentary House of Style: Music, Models and MTV. She has also written comic books for Marvel and Vertigo and hosts a podcast on jobs called Hey, Cool Job. It's available on iTunes.