New Scientist tries to rouse the secrets of anesthesia – and what being put under can teach us about consciousness itself:
A team led by Andreas Engel at the University Medical Center in Hamburg, Germany, have been investigating this process in still more detail by watching the transition to unconsciousness in slow motion. Normally it takes about 10 seconds to fall asleep after a propofol injection. Engel has slowed it down to many minutes by starting with just a small dose, then increasing it in seven stages. At each stage he gives a mild electric shock to the volunteer’s wrist and takes EEG readings.
“Long-distance communication seems to be blocked, so the brain cannot build the global workspace,” says Engel, who presented the work at last year’s Society for Neuroscience meeting in San Diego. “It’s like the message is reaching the mailbox, but no one is picking it up.”
What could be causing the blockage? Engel has unpublished EEG data suggesting that propofol interferes with communication between the primary sensory cortex and other brain regions by causing abnormally strong synchrony between them. “It’s not just shutting things down. The communication has changed,” he says. “If too many neurons fire in a strongly synchronised rhythm, there is no room for exchange of specific messages.”
The rhythm of oblivion.