…“The brain has to operate on this knife’s edge between excitability and chaos,” said Earl Miller, professor of neuroscience at MIT’s Picower Institute for Learning and Memory and the study’s co-corresponding author. “It’s got to be excitable enough for its neurons to influence one another, but if it gets too excitable, it spins off into chaos. Propofol seems to disrupt the mechanisms that keep the brain in that narrow operating range.”

Many theories of consciousness focus on the brain’s network structure, which integrates information and links different parts of the organ. One prominent theory suggests that awareness comes from an ‘ignition,’ an input that produces pulses of activity – or spikes – throughout the brain. Here, the researchers hypothesized that a critical factor in consciousness was the concept of ‘dynamic stability,’ the brain’s operating range that Miller referred to, and that propofol, and possibly other anesthetics, interfere with that stability.

Measuring dynamic stability as someone enters unconsciousness would enable researchers to determine if the unconscious state results from too much or too little stability. In other words, does a general anesthetic cause the brain to become too stable and unresponsive, which causes unconsciousness, or is unconsciousness caused by anesthetic brought about by a state of overexcitement and chaos? Previous studies have produced conflicting results, with some saying that anesthetics cause stability and some saying chaos.

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