Scientists Seek the Roots of Consciousness in the Brain

What happens to your brain as it slips into unconsciousness? A new technique allows researchers to view real-time 3-D images of a patient undergoing anesthesia using the drug propofol, and the findings show that consciousness isn't suddenly switched off, but rather fades as though a dimmer is being dialed down.

The research also suggests that consciousness resides in the connections between multiple parts of the brain, not in any single region. The images show that changes in the anesthetized brain start in the midbrain, where certain receptors for a neurotransmitter called GABA are plentiful.



Drugs like propofol act on these GABA A receptors, mimicking and enhancing the effects of GABA, which inhibits cellular activity. From the midbrain, changes move outward to affect the whole brain; as propofol's message spreads from region to region, consciousness dissolves.

"Our jaws ricocheted off the ground, and I won't say the words we used when we first saw the video," says lead author Dr. Brian Pollard, professor of anesthesia at the University of Manchester, who presented the results at the European Anesthesiology Conference in Amsterdam on Saturday. "We just sat there and stared, dumbfounded and kept repeating it. We're the first people in the world ever to see the brain becoming unconscious, that's quite a sobering thought."

Although anesthesia has been widely used since 1846, when a dentist first demonstrated the effects of ether at Massachusetts General Hospital, until recently very little has been understood about how it works. Even though scientists know that anesthetic drugs like propofol affect GABA in the brain, how that actually eliminates consciousness still remains a mystery.

Pollard explains, however, that propofol alters "the balance between inhibition and excitation in the brain," shifting the balance of activity toward the inhibitory circuits. At first, this produces a paradoxical result.