Paralyzed Man Was Awake for 23 Years, Not in Vegetative State

Difference Between Vegetative and Conscious State

For example, a person who is in a vegetative state and a person who is "locked-in" would both be paralyzed to some degree. Both patients would likely open their eyes and look around.

But, as Dr. James L. Bernat of the American Academy of Neurology explained, these two individuals would be considered to have two different definitions of "consciousness."

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"One is called wakefulness; eyes open, eyes moving -- that element is conducted primarily by the brainstem," Bernat said. "The second dimension of consciousness requires self-awareness -- they're aware of what's going on, they can feel, they can think.

"People in the vegetative state have only the wakeful dimension," he said.

A coma would be a state of full paralysis and full unconsciousness similar to the experience of going under anesthesia. Neurologists even define a third state in people with brain injuries as "minimally conscious," which is a state of semi-wakefulness and limited self-awareness.

In a minimally conscious person, "there may be parts of the brain that are able to generate certain types of thoughts similar to what a conscious person would do, but they're still quite devastated and quite injured," said Dr. Paul M. Vespa, director of Neurocritical Care at the David Geffen School of Medicine at the University of California, Los Angeles.

"There are probably a very small number of patients who are in this minimally conscious state. The exciting thing is, is that maybe there's a potential for rehabilitation," said Vespa.

Researchers, like Laureys, will have to do more work to define which brain image results from a functional MRI or PET machine are signs of a response, and which are random noises, before such progress could happen.

"We're not at the point where you can just throw somebody in the scanner and come up with the answer," DeGeorgia said. "[We] don't know how to interpret these [scans], because there have only been a few studies, and you have to know what is normal, and what is within the bell-shaped curve."

ABC News' Christophe Schpoliansky contributed to this report.