For the evening’s first demonstration, Siegel helped attach electrodes to the temples of Adam Goyer, a volunteer test subject, then cued Eugene Sinkevich, an electrical engineer, to start the current. “We are at the frontier,” Siegel said, looking out at the crowd as no more than two milliamps ran through Goyer’s head. “We’ll be able to tell our kids that we used to hook up arbitrary electrical signals to our brain.”Goyer sat still for several minutes, flinching only slightly. Then it was over. How did he feel?“First, let me say I’m really nervous about putting electricity through my brain. The first wave felt like a tingling on my forehead, and I guess I’m smarter afterward, sure. Then the second wave of tACS [transcranial alternating-current stimulation, a type of stimulation in which the flow of the charge varies] I kinda felt woozy, not in a bad way, but kind of like I’m on a boat. Then the third one, I definitely had some flickering, some eye flickering: in the outside of your eyes it’s like a flash, like a strobe.”

Source: An Evening with the Consciousness Hackers – The New Yorker