Nitrous oxide has been used for hundreds of years in anesthesiology, and in recent times has emerged as a recreational legal high, but until now no one has been quite sure of how the drug, commonly known as laughing gas, actually alters people's brains. Researchers from MIT have been able to reveal, however, that the drug makes key changes in patients' brainwaves.

At anesthetic doses, the scientists found that for around three minutes after being given nitrous oxide, the patient’s brains showed “large-amplitude slow-delta waves” that would sweep from the front to the back of the brain once every 10 seconds. This frequency of brainwaves is normally seen in people who are in a deep stage of sleep, but the interesting thing was that those waves induced by the laughing gas were around twice as large as those seen in natural sleep.

“We literally watched it and marveled, because it was totally unexpected,” explained Emery Brown, professor of Medical Engineering at MIT, who co-authored the study published in Clinical Neurophysiology. “Nitrous oxide has control over the brain in ways no other drug does.”

Nitrous oxide is not normally used exclusively to put patients under during operations. Normally, it’s used either at the end of the procedure as the more potent anesthetics clear from the system or sometimes mixed in with the main anesthetic gas to allow doctors to use a lower dose.

The researchers first noticed the effects of the nitrous oxide when Brown started recording the brain activity of patients under anesthetics using an electroencephalogram (EEG). He used stickers containing electrodes stuck to their heads to measure the changes in electrical activity that occur as neurons in the brain communicate. To suddenly discover such a finding after hundreds of years of using the gas surprised even Brown: “It's hard to imagine that in 2015 you can just anecdotally observe this.”

Brown thinks that the gas might block signals from the brainstem that normally keep individuals awake. Nitrous oxide is known to bind to receptors in the thalamus and cortex regions of the brain that typically receive signals from the arousal centers of the organ, and interrupting these can cause loss of consciousness, which is indicated by slower brainwaves.

The scientists are still puzzling over why these brainwaves only seem to happen in the first three minutes, even when the patients are continuously breathing in nitrous oxide, though it could be that the body gets rapidly habituated to it. Brown, however, thinks that if they can somehow manage to maintain this deep, slow-wave activity of the brain, then laughing gas could be used as a potent anesthetic in its own right, and one that would have fewer side effects than current gases.