Brain-computer interfaces in the continuum of consciousness.
OBJECTIVE
To summarize recent developments and look at important future aspects of brain-computer interfaces.


RESULTS
Recent brain-computer interface studies are largely targeted at helping severely or even completely paralysed patients. The former are only able to communicate yes or no via a single muscle twitch, and the latter are totally nonresponsive. Such patients can control brain-computer interfaces and use them to select letters, words or items on a computer screen, for neuroprosthesis control or for surfing the Internet. This condition of motor paralysis, in which cognition and consciousness appear to be unaffected, is traditionally opposed to nonresponsiveness due to disorders of consciousness. Although these groups of patients may appear to be very alike, numerous transition states between them are demonstrated by recent studies.


CONCLUSIONS
All nonresponsive patients can be regarded on a continuum of consciousness which may vary even within short time periods. As overt behaviour is lacking, cognitive functions in such patients can only be investigated using neurophysiological methods. We suggest that brain-computer interfaces may provide a new tool to investigate cognition in disorders of consciousness, and propose a hierarchical procedure entailing passive stimulation, active instructions, volitional paradigms, and brain-computer interface operation.
Kübler
Andrea
A
Institute of Medical Psychology and Behavioural Neurobiology, University of Tübingen, Tübingen, Germany. andrea.kuebler@uni-tuebinger.de
Kotchoubey
Boris
B
D001676:Biofeedback, Psychology / Q000379:methods / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology / Q000503:physiopathology*; D003143:Communication Devices for People with Disabilities / Q000639:trends; D003201:Computers / Q000639:trends*; D003243:Consciousness / Q000502:physiology; D003244:Consciousness Disorders / Q000175:diagnosis* / Q000503:physiopathology* / Q000628:therapy; D004185:Disability Evaluation; D006801:Humans; D008328:Man-Machine Systems; D014584:User-Computer Interface