Editor's note: This article originally referenced researchers' claims that a 24mg/kg dose of ketamine was "at the lower end of the range used recreationally." VICE understands the researchers have since submitted an addendum to the publication to clarify that "the dose ranges for recreational users seeking psychedelic effects are much lower, typically 0.5-1mg/kg." We have removed all reference to the original claims.
Researchers studying the effects of ketamine on sheep might have accidentally discovered the reason people k-hole.
A team of scientists from the University of Cambridge were measuring the brain waves of the sedated animals as part of a study aimed at understanding the effect of therapeutic drugs on people with Huntington's disease: a condition in which nerve cells in the brain break down, leading to motor, cognitive, and psychiatric complications.
For the first and second phases of the experiment, researchers administered 12 mg/kg of ketamine to the sheep and monitored their brain activity both while they were anaesthetised and as the drug gradually wore off. For the third phase, the researchers monitored the brain activity of six of the 12 sheep after they were given a single ketamine dose of 24mg/kg.
What they found was that the sheep displayed “unusual” brain wave activity while they were coming out of sedation—which likely accounts for the dissociative and hallucinatory effects of a ketamine high—while the brain waves of sheep that were given a more intense dose appeared to stop altogether for a period of several minutes—a “pause” which the researchers believe might explain the experience of a k-hole.
Ketamine, or so-called “horse tranquilliser”, is commonly used as an anaesthetic on humans as well as animals in clinical settings. But over the past 60 years, it’s also become a popular recreational substance for precisely the same trippy, dissociative effects observed in the Cambridge study.
Unsurprisingly, the brain activity of the sheep was in a state of low frequency while they were asleep—but as the ketamine wore off and the sheep regained consciousness, their brain activity started switching between high and low frequency oscillations. Scientists note it is during this phase that ketamine users report hallucinations.
"As the sheep came round from the ketamine, their brain activity was really unusual," said Professor Jenny Morton, who led the research. "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.
"It's likely that the brain oscillations caused by the drug may prevent information from the outside world being processed normally."
It was when some of the sheep were given a high dose of ketamine, though, that things became really interesting. Within two minutes of receiving the 24mg/kg dose, the brain activity of five of the six sheep stopped completely. One of the sheeps’ brains stopped for several minutes.
"This wasn't just reduced brain activity,” said Professor Morton. “After the high dose of ketamine the brains of these sheep completely stopped. We've never seen that before."
While the sheep reportedly appeared to be sleeping, it was observed that their brains were entirely offline. When their brain activity resumed, it was again in the alternating bursts of low and high frequency activity that are thought to produce the hallucinatory effects of the drug.
”A few minutes later their brains were functioning normally again,” said Morton. “It was as though they had just been switched off and on."
Anecdotally, k-holes are commonly compared to near death experiences, with users frequently describing a phenomenon known as “ego death”—when one’s sense of existence and self completely dissolves—followed by feelings of intense serenity, acceptance, and bliss. The Cambridge researchers conclude that the brain phenomena they observed might explain these effects for the very first time.
“Measurements of the brain waves of sheep sedated by [ketamine] may explain the out-of-body experience and state of complete oblivion it can cause,” the study’s authors proclaim. “The dissociative state induced by ketamine almost certainly underlies its appeal as a recreational drug … [and] it seems likely that the total cessation of cortical activity underpins the phenomenon known as the ‘k-hole’ … described and keenly sought by ketamine abusers.”
“Better awareness of the effects of ketamine on the brain would greatly aid our understanding of its use, not only as an anaesthetic, analgesic or antidepressant but also as a drug of abuse,” they add, noting that “the precise physiological mechanisms through which ketamine exerts its effects are unknown.”