Drifting off

Consciousness is surprisingly hard to define

It seems like it should be obvious because we experience consciousness all the time.  But our experiences, while interesting, are not, in and of themselves, scientific evidence.  And the science is not yet definitive. As we reported in our consciousness program some researchers believe that, while there is an evolutionary reason for our highly developed minds, there may not be a reason for us to understand how the brain produces that mind.  Is consciousness the same as self-awareness, or attention, or sensation?  Are these subsets of consciousness?  What about the subconscious or nonconscious aspects of our existence?  Philosophers and scientists have been arguing over the definition of consciousness for hundreds of years, if not longer, with no end in sight.

We aren't totally conscious 100% of the time

You, sitting there reading these words, have a much different level of consciousness than, say, a boxer after a knockout punch, a frat boy after one jello shot too many or a patient on the operating table under general anesthesia. And then there's the most familiar shift in consciousness of all, the one that takes up a third of our lives and doesn't require a hangover or a bruise: sleep. Sleep is a dramatic change in consciousness, and perhaps the easiest one to study, since it happens, more or less reliably, every 24 hours in humans and many other living creatures .

What happens during sleep that makes the experience so different from being awake?

Your brain is a huge community of cells, using electrical signals to talk with one another through a complex network of connections.  You might think that, when sleeping, your neurological machinery shuts off -- "out like a light."  But, even during dreamless (NREM) sleep, there's a lot going on.  Scientists can see this using tools that measure the electrical activity at the cortical surface.  Clearly, it is more than just the overall amount of brain activity that determines consciousness.

So much for the out-like-a-light hypothesis.

How does this help us understand consciousness? We might get a clue from Marcello Massimini, Giulio Tononi and their colleagues at the University of Wisconsin, Madison.

They outfitted subjects with special caps covered in sensors so they could see which parts of the brain's surface were sending the strongest signals at any given moment. Then they used a strong, focused pulse of magnetism to create an electrical impulse in a specific spot on the brain's surface, and watched as the brain reacted.

But things got interesting when the researchers gave the exact same magnetic pulse to sleeping subjects. Their brains looked like a city where the phone lines had gone down: the juicy-gossip tidbit of neural activity spread only into the immediate vicinity -- to the neighbors over the backyard fence, you might say, who didn't care as much as friends across town might. The activation died out altogether in just half the time than it had in waking subjects.

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