"It's common for family members to feel that their loved ones are aware. Part of it is motivated by the love they have for the person -- they want to interpret any indication as a sign that they are aware," he said.
David Gibbs, the attorney for Schiavo's parents, who wish to keep her on life support, has argued that Schiavo may be in a semiconscious state known as a minimally conscious state. This state of consciousness was first defined in 1996 as a transitional state indicating either improvement in consciousness or deterioration in the level of consciousness.
In this condition, patients show occasional moments of awareness, such as attempting to communicate through speaking, writing or using yes/no signals (other than eye blinks). A recent study in the journal Neuroscience revealed that people in this state may be quite aware, although trapped in a body that is largely nonfunctioning.
The researchers from New York Presbyterian Hospital used brain imaging technology to show that, when played audiotapes of their loved ones' voices, people in this state have brain activity similar to that of a fully conscious person. However, when no recording was played to the patients, their brain activity was less than half that of healthy people.
"These are patients who show episodic consciousness," said Fins. "They may be saying a word or smile, but it is intermittent."
An estimated 100,000 to 300,000 Americans have been diagnosed with being in this transitional state and some patients have emerged from the condition to reach a fuller consciousness. But neurologists are quick to point out that there are important distinctions between those in a semiconscious state and those in a persistent vegetative state.
"The difference is between autonomic activity and episodic conscious activity," said Fins. "It's something that can be observed by a neurologist or detected on a brain scan. It's not a diagnosis that legislators can make after viewing videotapes."