Consciousness and paralysis

This chapter reviews measurement of and interventions by brain-computer interface (BCI) in different states of consciousness associated with severe neurological diseases. The two dimensions of consciousness are awareness and wakefulness. Patients in a vegetative state (VS) and with locked-in syndrome (LIS) do not differ in their wakefulness but with regard to awareness, they are polarized on two extremes of the continuum. Event-related potentials (ERPs) and electric brain oscillations in electroencephalography (EEG), magnetoencephalography (MEG), and electrocorticography (ECoG) reflect information processing mechanisms in the brain. These cortical responses help to describe disorders of states of consciousness such as vegetative state, coma and locked-in syndrome. They can also be used for controlling a brain-computer interface (BCI). BCIs translate brain signals into computer commands such as cursor control or selection of letters for communication and control of external devices, e.g. robots or movement prosthesis. Paralyzed people and patients with LIS can use BCIs for communication and environmental control. By applying operant and classical conditioning the users learn to regulate their brain activity in order to operate BCIs even with advanced LIS and probably with complete locked-in syndrome (CLIS). Current research investigates the potential of BCIs for differential diagnosis and assessment of non-responsive patients. In the approach described here, a hierarchical paradigm including passive and active stimulation, instructions, volitional tasks and decision making with a BCI indicates preserved or absent cognitive abilities.