vegetative state
a condition in which a person appears awake but lacks any self-awareness, environmental awareness, or basic or higher level cognitive functions (e.g., information processing, language comprehension and production, perception). The individual exhibits normal reflexes, circadian rhythms (including sleep–wake cycles), respiration, circulation, and other brainstem- and hypothalamus-governed functions but shows no voluntary behavior or other purposeful response to stimuli. Additionally, electroencephalography often reveals slowed electrical activity. Typically associated with destruction of vast areas of cerebral cortex or its integrating connections as a result of trauma, the condition is most often seen following coma but also occurs in those who have various degenerative disorders or severe congenital malformations of the nervous system. A persistent vegetative state (PVS, or persistent noncognitive state) is one
lasting more than four weeks from which there is the possibility—however slim—of recovery, whereas a permanent vegetative state is one lasting more than three to 12 months (depending upon cause) from which there is no chance of regaining consciousness. The vegetative state is distinct from both brain death and the minimally conscious state but nonetheless is misdiagnosed as the latter nearly half the time. The assessment of residual cognitive abilities is extremely difficult, and uniform assessment protocols for the vegetative state have yet to be established. However, advanced functional neuroimaging techniques (e.g., event-related potentials, functional magnetic resonance imaging) are being investigated as a source of information beyond the traditional clinical method to aid diagnosis, and several recently developed measures using structured behavioral observations, such as the Sensory Modality
Assessment and Rehabilitation Technique (SMART) and the Wessex Head Injury Matrix (WHIM), are now available. [defined in 1972 by British neurologist William Bryan Jennett (1926–2008) and U.S. neurologist Fred Plum (1924–2010)]