Few video games are more basic than Pong, but Cornell University researchers built a custom electroencephalography (EEG) device so they could control the game's on-screen paddle with their minds. The alpha waves that EEG machines read are faint electrical signals.
They ran the EEG readings through an amplification circuit to filter and boost the signals. Spiking alpha waves produced during relaxation move a player's paddle up, and smaller waves, indicating concentration, move it down. The size of the waves determines how much the paddle moves.