State of Oblivion Resulting from Ketamine Use Explained

Researchers from the University of Cambridge have identified two brain phenomena that shed light on some of the side effects of ketamine. Their measurements of the brain waves of sheep sedated by the drug may explain the out-of-body experience and state of complete oblivion it can cause.

In order to understand the effect of therapeutic drugs on the brains of people living with Huntington's disease, researchers used electroencephalography (EEG) to measure immediate changes in the animals' brain waves once ketamine—an anaesthetic and pain relief drug—was administered. Low frequency activity dominated while the sheep were asleep. When the drug wore off and the sheep regained consciousness, the researchers were surprised to see the brain activity start switching between high and low frequency oscillations. The bursts of different frequency were irregular at first, but became regular within a few minutes.

"As the sheep came round from the ketamine, their brain activity was really unusual," said co-author Jenny Morton. "The timing of the unusual patterns of sheep brain activity corresponded to the time when human users report feeling their brain has disconnected from their body." 

The findings arose as the team wanted to understand why human patients respond differently to various drugs if they carry the gene for Huntington's disease. Sheep were used because they are recognized as a suitable preclinical model of disorders of the human nervous system.

Six of the sheep were given a single higher dose of ketamine, 24mg/kg. This is at the high end of the anaesthetic range. Initially, the same response was seen as with a lower dose. But within two minutes of administering the drug, the brain activity of five of these six sheep stopped completely, one of them for several minutes. "This wasn't just reduced brain activity. After the high dose of ketamine the brains of these sheep completely stopped. We've never seen that before," said Morton. Although the anesthetized sheep looked as though they were asleep, their brains had switched off. "A few minutes later their brains were functioning normally again—it was as though they had just been switched off and on."

The researchers think that this pause in brain activity may correspond to what ketamine abusers describe as the 'K-hole'—a state of oblivion likened to a near-death experience, which is followed by a feeling of great serenity. The study was published today in Scientific Reports.