NEW YORK — In the family video played over and over on TV, Terri Schiavo seems to gaze fondly at her mother, with the hint of a smile.

On Sunday night, as Congress took up debate on her case, her father told reporters that she responded to his teasing by making a face at him. "It tells us she's still with us," he said.

But in Schiavo's condition, described as a persistent vegetative state, family members can be deceived by things like eye movements and reflexes, experts say.

"It creates this ironic combination of wakefulness without awareness," said Dr. James Bernat, a neurology professor at Dartmouth Medical School.

Function, non-function

That's because in a persistent vegetative state, the brain centers that control wakefulness are functioning, but those that permit conscious awareness of oneself or the environment are damaged or destroyed.

Such patients close their eyes to sleep and open them to awake. If a doctor brushes the eyeball with a wisp of cotton, they may blink. If something gets caught in the throat, they cough. There may be limited eye movements, though patients can't follow a person walking from one side of the room to another, for example.

That's in contrast to a coma, in which the eyes remain closed and a person is neither aware nor awake, or brain death, in which there is no sign at all that the brain is functioning.

False hopes?

Bernat, past chairman of the American Academy of Neurology's Ethics, Law and Humanities Committee, declined to comment specifically on the Schiavo case. He said outward signs of persistent vegetative state can give family members false hope.

"There's a normal tendency of family members to interpret [random] movements as evidence of awareness," said Bernat, who recalled seeing that happen with his own patients.

"To the families and loved ones, and to inexperienced health-care professionals, PVS patients often look fairly 'normal' " said Dr. Ronald Cranford, a neurologist and bioethicist at the University of Minnesota Medical School.

"Their eyes are open and moving about during the periods of wakefulness that alternate with periods of sleep; there may be spontaneous movements of the arms and legs, and at times these patients appear to smile, grimace, laugh, utter guttural sounds, groan and moan, and manifest other facial expressions and sounds that appear to reflect cognitive functions and emotions, especially in the eyes of the family."

Bernat said that when family members claim that a loved one in a persistent vegetative state is purposefully looking at them, he asks to accompany them to the bedside and see for himself. Sometimes, in fact, family members really have noticed genuine signs of consciousness and investigation shows the diagnosis was incorrect, but in his experience, he said, most of the time the family has been wrong.

Doctors try to help the family understand how it's possible to be awake but not aware, he said.

Patients can recover after even a year or two in a persistent vegetative state caused by head trauma, Bernat said, although they generally continue to be disabled. However, he said a vegetative state that was caused by lack of blood or oxygen delivery to the brain and has gone on more than five years is considered permanent. No one has ever come back from such a condition, according to the American Academy of Neurology.

Grim statistics

"Approximately 10,000 to 25,000 adults and 6,000 to 10,000 children in the United States are diagnosed as being in the persistent vegetative state," the Multi-Society Task Force on Persistent Vegetative State says in its 1995 guidelines on the condition, the latest available.

"Survival beyond 10 years is unusual. The chance for survival of greater than 15 years is approximately 1 in 15,000 to 1 in 75,000," it adds.

Video showing the dark-haired woman appearing to interact with her family has been televised nationally. But a court-appointed doctor has said the noises and facial expressions are only reflexes.

Usually patients can breathe without a ventilator. As in the Schiavo case, long-term care involves a feeding tube to the stomach. If family members ask to stop treatment, the tube is removed or medical teams are instructed not to treat infections, Bernat said.

Experts say Terri Schiavo would experience no discomfort if allowed to die, as the part of her brain that experiences pain is unlikely to be functioning.

Quotes from Dr. Cranford were reported by Reuters.