Consciousness, are there more than three states?

YOU might think consciousness is li ke a light switch, either on or off. But the true picture now seems rather murkier, challenging our notions of awareness and free will, as well as raising issues of consent in coma patients. People used to think just three states of consciousness existed, says Adam Zeman of the Peninsular Medical School in Exeter, U K. “You’re either awake or asleep – and if you’re asleep you’re either in dream or nondream sleep,”
But brain imaging suggests there are more. Take sleepwalking, which affects as many as 1 in 20 adults. “The sleepwalking brain is literally in a half-awake, half-asleep, state,” says Zeman.Researchers once manoeuvred a sleepwalker into a brain scanner, and while they saw that much of the cortex – involved in awaereness and consciousness was offline, other brain areas were active, including those linked with emotion.
Similar overlaps might explain other weird states of consciousness. In dreaming sleep – also known as REM sleep –  we lie still be because an area of brainstem called the pons blocks signals to the muscles. People with REM behavior disorder lose this inhibition and physically act out of their dreams. To opposite condition,known as sleep paralysis, occurs if people wake up while still unable to move.
There may also be hither unnoticed stopping-off points in the twilight between consciousness and coma. In February, a team led by Adrian Owenatthe University of Cambridge discovered that it was possible to communicate with a man in a vegetative state in which, someone has intact reflexes and can breath unaided, but seems completely unaware of their surroundings. By asking him to visualise playing tennis or moving around the house as he lay in a brain scanner, they were able to elicit yes or no answers from him. Such patients are currently treated as unconscious, but if they can understand questions and communicate, they might be able to express opinions about their treatment – and whether or not it should be withdrawn.
We may not yet know how many states of consciousness there are, but the nature of consciousness is looking increasngly like ladder rather then a light switch.
source: Linda Geddes in recent issue of New Scientist. April 3-9/2010

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