Brain-activated computer system. Girl using a brain-activated system to play a computer game. A MindDrive sensor (black) on her finger monitors her mental activity. This is done by measuring electrical signals in her skin, along with her heartbeat, temperature and blood pulse volume. A computer program filters out unconscious nerve impulses and only responds to conscious signals. It is hoped that MindDrive will allow more complex computer software to be operated. The system can also be used to show the mental states of people who cannot describe them themselves, for example babies and patients during surgery.