People with locked-in syndrome cannot move their limbs or talk because of a motor impairment, but remain conscious and intellectually awake. Restoring the ability to communicate to people with locked-in syndrome will have a positive effect on their quality of life, will enable them to reintegrate into society and increase their capacity to lead productive and fulfilling lives. This study sims to develop a new assisted communication device based on a brain-computer interface, a system that allows the user to control a computer with his brain activity. The investigators will develop this brain-computer system for long-term stability and independent use by using adaptive decoders. The investigators will test the long-term stability and independence of this system with healthy volunteers, people with tetraplegia and people with locked-in syndrome over time periods of several months.