Patients in a vegetative state are awake, not in a coma, but have no awareness because of severe brain damage.

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"We have seen patients make remarkable improvements after being in a coma for a long time, but the best prognostic indicator is how one does over time, " Black said.

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Dr. Daniel Hanley, professor of neurology at Johns Hopkins Medicine, in Maryland, told CNN that VS is a coma-like state in which patients have a sleep and wake cycle, and can show reflex chewing, swallowing and blinking, but don't respond to language or stimulation.

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As with many such patients, the congresswoman was placed in a medical coma and on a ventilator to allow the brain to recover.

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So, Laureys and his team studied the near-death memories of people who survived -- in particular those of coma patients -- with the help of a psychological examination.

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