- Picturing awareness
- A rare mistake?
- A spectrum of awareness
- A new class of consciousness
- Silent witness
- The future of consciousness imaging
This chapter is from the book
This chapter is from the book
This chapter is from the book
A spectrum of awareness
Even if the young English woman's story proves a rare case, it has prompted concern over whether standard bedside tests for the vegetative state are reliable and whether the boundaries between states of consciousness are clear at all.
The persistent vegetative state (PVS), as we currently understand it, lies on a continuum of impaired brain function. Though neither comatose nor brain dead, vegetative patients are unaware of themselves and their surroundings; they are alive without consciousness. They can wake and fall asleep, but they cannot communicate or respond to commands in a meaningful way. The thinking, feeling part of the brain (the cerebral cortex) no longer functions, but the more primitive part of the brain governing reflexes (the brainstem) still operates. Isolated areas in the cortex may still show activity, but they are disconnected from parts of the brain necessary for conscious perception.
"There are islands of activity in a sea of silence,"20 says Steven Laureys, who has taken PET scans of diverse states of awareness in the hopes of identifying regions in the cerebral cortex—and connections among these regions and other parts of the brain—that may prove crucial to maintaining the experience of consciousness.
Vegetative patients like Theresa Schiavo are often mislabeled as comatose or brain dead, though their brainstems are still fully operative, allowing their hearts and lungs to work and producing sleep-wake cycles. A comatose patient lingers in a state of profound unconsciousness from which she cannot be roused—even by powerful stimulation—whereas brain death entails total and permanent loss of all brain function and is one of the medical and legal definitions of death. Patients who are brain dead can no longer breathe for themselves, and their hearts will stop beating if they do not receive oxygen from mechanical ventilation. Despite these significant distinctions, a surprising 1996 survey published in the Annals of Internal Medicine revealed that almost half of U.S. neurologists and nursing home medical directors believed that patients in a vegetative state could be declared dead.21
Current diagnostic guidelines allow patients to be declared permanently vegetative after one year if they have suffered traumatic brain injury (like the young English patient) or after six months if they have suffered brain injury due to oxygen deprivation (like Theresa Schiavo). Rarely, people with oxygen-related brain damage have regained consciousness after being diagnosed as permanently vegetative, but all of those patients recovered within two years. In a few astonishing cases, vegetative patients with traumatic brain injuries have regained consciousness much later. Terry Wallis, an Arkansas mechanic, recovered awareness in 2003, more than 18 years after a serious car accident. Mr. Wallis, many neurologists now believe, would have been more accurately described as "minimally conscious."