Doctors could tell Houben was not in a vegetative state, but they couldn't tell from scans alone exactly how conscious he was. He could be "locked-in," meaning he was fully conscious and aware but too paralyzed to communicate, or he could be what's called "minimally conscious."
Unlike a coma or a vegetative state, neurologists define a third state in people with brain injuries as "minimally conscious," which is a state of semi-consciousness and limited self-awareness.
In 1994, an article in the New England Journal of Medicine estimated there were 15,000 to 30,000 people living in a vegetative state in the United States. A 2002 article in the journal Neurology estimated between 112,000 to 280,000 people in the United States are living in what is known as a "minimally conscious" state.
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," Vespa said. "The exciting thing is, is that maybe there's a potential for rehabilitation."