It is judged to be permanent after three months if induced nontraumatically. After 3 months, recovery is rare and life expectancy is approximately 2 to 5 years.

Patients in a persistent vegetative state do not feel pain, nor do they "suffer," says Michael De Georgia, MD, head of the neurology-neurosurgery intensive care unit at the Cleveland Clinic Foundation here.

Pain, as well as suffering, requires consciousness, which is lacking in a person in a persistent vegetative state, says Dr. De Georgia.

"Certainly these patients don't suffer," he adds. "Suffering is really that whole emotional aspect of pain: fear, anxiety, panic surrounding pain. You have to have consciousness to experience these emotions. So just as a person in a persistent vegetative state can't experience pain because of a lack of consciousness, they also don't suffer."

The issue of the potential pain and suffering of Schiavo, 41, the Florida woman who doctors say has been in a persistent vegetative state for 15 years, has become a national cause celebre. On Friday doctors at a Florida hospice removed Ms. Schiavo's feeding tube after a Florida judge approved the action. Since then President Bush signed a rapidly approved law that puts her fate in the hands of a federal court judge. A federal judge in Florida then refused to order doctors to reinsert the feeding tube, and the Schindlers' lawyers said they intend to appeal immediately to the 11th U.S. Circuit Court of Appeals based in Atlanta.

This marks the third time Ms. Schiavo has been taken off enteral nutrition during a long and contentious legal battle between her husband - Michael Schiavo who says his wife would want the tube removed - and Ms. Schiavo's parents who steadfastly maintain that their daughter would not want the tube removed. The parents, Bob and Mary Schindler, say their daughter responds to them and is not in a persistent vegetative state.

Dr. De Georgia says that a patient in a persistent vegetative state can experience arousal, meaning that the patient's eyes may be open and the patient may laugh, cry or appear to track someone who is in the room.

And that is what can be confusing for people, especially relatives, he says. "For example, a patient in persistent vegetative state will grasp your hand. In fact if you put anything into the patient's hand, the hand will grasp it. But this is a very primitive reaction. A newborn baby will grasp your finger, but there is no consciousness."

It is consciousness that determines whether one can "feel" pain in the sense that most people understand when they talk about feeling pain.

This doesn't mean that a patient like Terri Schiavo won't respond to pain stimulus - if you pinch her arm, she is like to flinch away. "That is called nociception," De Georgia says. "Tissue is damaged by the pinch, this generates a response in a receptor, which sends an impulse along the peripheral nerves. This impulse travels to the thalamus, which directs the arm to withdraw," he said. It is what is commonly called a reflex.

Pain, on the other hand, is the recognition of nociception by the nervous system, which sends the impulse to regions of the brain where consciousness exists. In the case of a severely brain injured person - one in a persistent vegetative state - those areas of consciousness have been destroyed, and as result "they don't 'feel' pain."