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Consciousness Unbound

Some researchers say the key to learning how anesthetics work is to examine a much tougher subject: consciousness.

Charles Slack // Portraits by Eric Ogden // Summer 2006

Investigating how anesthesia produces unconsciousness has led researchers to tackle an even more fundamental question: How does consciousness work?

Brain activity continues whether someone is awake, asleep or anesthetized. But only in a conscious state does that activity coalesce into the ability to think and act deliberately—a process neuroscientists call cognitive binding.

“Think about drinking a cup of coffee,” suggests George Mashour, chief resident in anesthesia and critical care at the Massachusetts General Hospital. “You experience a certain shape, color, feel, smell and taste. Each of these attributes is processed in a different area of the brain—but how are they all assembled to form your unified experience of drinking coffee?”

One theory is that certain neurons specialize in collecting and processing input from sensory neurons bringing information from the eyes, ears, tongue and skin. If your brain were a factory, Mashour says, these neurons would form a sort of final assembly area, using “parts” supplied by sensory neurons around the brain to make the finished product: conscious thought. Another theory compares neurons to orchestra musicians, each processing its own type of information, and the brain’s thalamus to the conductor, which coordinates the neurons to produce a symphony of organized thought.

Such theories are a long way from proven, but Mashour, who earned a Ph.D. in neuroscience before turning to anesthesiology, thinks they provide a good model for investigating how anesthetics work. Somehow, he says, anesthetic drugs reverse the brain’s ability to bind varied sensory inputs into conscious thought. The brain is still receiving signals but can’t assemble them. That’s why he calls anesthesia “consciousness unbound.”


Understanding Anesthesia

The waning of consciousness during surgery is as mysterious as it is routine. Finally, the curtain may be about to part.

Number Conscious

The bispectral index uses EEG readings to assign a number to a patient's level of consciousness, allowing doctors to administer more precise doses of anesthesia.

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