Modeling the minimally conscious state: measurements of brain function and therapeutic possibilities.

The minimally conscious state (MCS) defines a functional level of recovery following severe brain injuries. Patients in MCS demonstrate unequivocal evidence of response to their environment yet fail to recover the ability to communicate. Drawing on recent functional brain-imaging studies, pathological data, and neurophysiological investigations, models of brain function in MCS are proposed. MCS models are compared and contrasted with models of the vegetative state (VS), a condition characterized by wakeful appearance and unconsciousness. VS reflects a total loss of cognitive function and failure to recover basic aspects of the normal physiologic brain state associated with wakefulness. MCS may represent a recovery of the minimal dynamic architecture required to organize behavioral sets and respond to sensory stimuli. Several pathophysiological mechanisms that might limit further recovery in MCS patients are considered. Implications for future research directions and possible therapeutic strategies are reviewed.