Does anyone remember the OCZ NIA ("Neural Impulse Actuator")?
It was a gaming input device, a simple headband that measured brain activity externally. For beginners, if you thought really hard of "pitch black" or "bright white," it could measure that and you had your first two thought-controlled buttons. Advanced users could train themselves all the way to several buttons and analog inputs, i.e. control joystick input through their mind.
(just Google/DDG "OCZ NIA" to watch some old review and test videos)