The “gray zone” is the twilight region between full consciousness and brain death. People with sustained brain injuries or victims of strokes or neurodegenerative diseases, such as Alzheimer’s and Parkinson’s are often in the gray zone. Many of them are oblivious to the outside world, and their doctors and families often believe they are incapable of thought. But 20 percent of them are conscious although they never respond to any form of external stimulation.
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