A persistent vegetative state (PVS) is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. After four weeks in a vegetative state (VS), the patient is classified as in a persistent vegetative state. This diagnosis is classified as a permanent vegetative state some months (three in the US and six in the UK) after a non-traumatic brain injury or one year after a traumatic injury. Today, doctors and neuroscientists prefer to call the state of consciousness a syndrome, primarily because of ethical questions about whether a patient can be called "vegetative" or not.
Most PVS patients are unresponsive to external stimuli and their conditions are associated with different levels of consciousness. Some level of consciousness means a person can still respond, in varying degrees, to stimulation. A person in a coma, however, cannot. In addition, PVS patients often open their eyes in response to feeding, which has to be done by others; they are capable of swallowing, whereas patients in a coma subsist with their eyes closed (Emmett, 1989).
Cerebral cortical function (e.g. communication, thinking, purposeful movement, etc) is lost while brainstem functions (e.g. breathing, maintaining circulation and hemodynamic stability, etc) are preserved. Non-cognitive upper brainstem functions such as eye-opening, occasional vocalizations (e.g. crying, laughing), maintaining normal sleep patterns, and spontaneous non-purposeful movements often remain intact.
PVS patients' eyes might be in a relatively fixed position, or track moving objects, or move in a disconjugate (i.e., completely unsynchronized) manner. They may experience sleep-wake cycles, or be in a state of chronic wakefulness. They may exhibit some behaviors that can be construed as arising from partial consciousness, such as grinding their teeth, swallowing, smiling, shedding tears, grunting, moaning, or screaming without any apparent external stimulus.
Individuals in PVS are seldom on any life-sustaining equipment other than a feeding tube because the brainstem, the center of vegetative functions (such as heart rate and rhythm, respiration, and gastrointestinal activity) is relatively intact (Emmett, 1989).
Dalton was in a PVS for three months in the Further, until Elise Rainier got him out. He was tired, but completely recovered. He died during a séance, though briefly.