Brain imaging suggested that the best way to do this would be to stimulate the motor cortex while the volunteer was doing the task. But McKinley and his team added a twist: after the stimulation, they use tDCS in reverse to inhibit the volunteers’ prefrontal cortex, which is involved in conscious thinking. The day after the stimulation, the volunteers are brought back for re-testing. “The results we’re getting are fantastic,” McKinley says. People getting a hit of both mid-test and inhibitory stimulation did 250% better in their retests, far outperforming those who had received neither. Used in this way, it seems that tDCS can turbo-boost the time it takes for someone to go from being a novice at a task to being an expert.