In the US, courts have required petitions before termination of life support that demonstrate that any recovery of cognitive functions above a vegetative state is assessed as impossible by authoritative medical opinion. In England, Wales and Scotland, the legal precedent for withdrawal of clinically assisted nutrition and hydration in cases of patients in a PVS was set in 1993 in the case of Tony Bland, who sustained catastrophic anoxic brain injury in the 1989 Hillsborough disaster. An application to the Court of Protection is no longer required before nutrition and hydration can be withdrawn or withheld from PVS (or minimally conscious – MCS) patients.This legal grey area has led to vocal advocates that those in PVS should be allowed to die. Others are equally determined that, if recovery is at all possible, care should continue. The existence of a small number of diagnosed PVS cases that have eventually resulted in improvement makes defining recovery as "impossible" particularly difficult in a legal sense. This legal and ethical issue raises questions about autonomy, quality of life, appropriate use of resources, the wishes of family members, and professional responsibilities. Signs and symptoms
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 recent years, a number of studies have demonstrated an important role for functional neuroimaging in the identification of residual cognitive function in persistent vegetative state; this technology is providing new insights into cerebral activity in patients with severe brain damage. Such studies, when successful, may be particularly useful where there is concern about the accuracy of the diagnosis and the possibility that residual cognitive function has remained undetected. Diagnostic experiments
Researchers have begun to use functional neuroimaging studies to study implicit cognitive processing in patients with a clinical diagnosis of persistent vegetative state. Activations in response to sensory stimuli with positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and electrophysiological methods can provide information on the presence, degree, and location of any residual brain function. However, use of these techniques in people with severe brain damage is methodologically, clinically, and theoretically complex and needs careful quantitative analysis and interpretation. For example, PET studies have shown the identification of residual cognitive function in persistent vegetative state. That is, an external stimulation, such as a painful stimulus, still activates "primary" sensory cortices in these patients but these areas are functionally disconnected from "higher order" associative areas needed for awareness. These results show that parts of the cortex are indeed still functioning in "vegetative" patients.In addition, other PET studies have revealed preserved and consistent responses in predicted regions of auditory cortex in response to intelligible speech stimuli.