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When patients are put under anaesthesia, they are often told they will be “put to sleep,” and now it appears that in some ways that’s exactly what the drugs do to the brain. New evidence in mice reported online on October 25 in Cur- rent Biology, a Cell Press publication, shows that the drugs don’t just turn wakefulness “off,” they also force important sleep circuits in the brain “on.” “Despite more than 160 years of continu-
ous use in humans, we still do not understand how anesthetic drugs work to produce the state of general anaesthesia,” said Max Kelz of the University of Pennsylvania. “We show that a commonly used inhaled anesthetic drug di- rectly causes sleep-promoting neurons to fire. We believe that this result is not simply a coin- cidence. Rather, our view is that many general anesthetics work to cause unconsciousness in part by recruiting the brain’s natural sleep cir- cuitry, which initiates our nightly journey into unconsciousness.”
Anaesthesia drugs really do put us to sleep Kelz is himself an anesthesiologist, and he
had long wondered just how accurate this no- tion of putting his patients to sleep really was. After all, there are important differences be- tween natural sleep and the unconsciousness that comes with anaesthesia. Even the sound- est sleeper can be roused, while anesthetised patients maintain their slumber
through the
incredible insults that surgeries unavoidably bring. In the new study, Kelz’s team focused on
a particular part of the brain, deep within the hypothalamus, which is known to increase in activity as one drifts off to sleep. Through a combination of direct electrical recording and other methods, they found that the anesthetic drug known as isoflurane boosts activity in this sleep-promoting brain area in mice. As further evidence of a connection, animals lacking the function of those neurons became more resis- tant to entering states of anaesthesia. The findings not only provide important
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clinical insights, but they might also go a long way toward reawakening our curiosity about anaesthesia—to say nothing of the very myste- rious nature of human consciousness itself. “The development of anesthetic drugs has
been hailed as one of humankind’s greatest dis- coveries in the last thousand years,” Kelz said. “Anesthetics are annually given to over 230 million patients worldwide. Yet as a society, and even within the anaesthesia community, we seem to have lost our curiosity for how and why they work.”
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