Out-of-body experiences are all about rhythm, a team reported Wednesday in the journal Nature.
In mice and one person, scientists were able to reproduce the altered state often associated with ketamine by inducing certain brain cells to fire together in a slow, rhythmic fashion.
"There was a rhythm that appeared, and it was an oscillation that appeared only when the patient was dissociating," says Dr. Karl Deisseroth, a psychiatrist and neuroscientist at Stanford University.
Dissociation is a brain state in which a person feels separated from their own thoughts, feelings and body. It is common in people who have some mental illnesses or who have experienced a traumatic event. It can also be induced by certain drugs, including ketamine and PCP (angel dust).
The study linking dissociation to brain rhythms represents "a big leap forward in understanding how these drugs produce this unique state," says Dr. Ken Solt, an anesthesiologist at Harvard Medical School and Massachusetts General Hospital. Solt is the co-author of an article that accompanied the study but was not involved in the research.
The finding also could be a step toward finding non-drug methods to control states of consciousness, Solt says.
Deisseroth's lab made the discovery while studying the brains of mice that had been given ketamine or other drugs that cause dissociation. The team was using technology that allowed them to monitor the activity of cells throughout the brain.
"It was like pointing a telescope at a new part of the sky," Deisseroth says. "And something really unexpected jumped out at us."
What jumped out was a very distinct rhythm produced by cells in an area involved in learning and navigation. Those cells were firing three times each second.
To learn more, the team used a tool called optogenetics, which Deisseroth helped invent. It uses light to control the firing of specific cells in the brain.
As a result, the team was able to artificially generate this rhythm in the brains of mice.
The mice then behaved as if they had been given ketamine. And once the slow rhythm began, the scientists could see that brain areas that had previously been working together were now out of sync.
We could see, right before our eyes, dissociation happening," Deisseroth says.
But that was in mice. Deisseroth wanted to know about people.
He got an opportunity, thanks to some good luck and sandwiches. The sandwiches, provided by Deisseroth, were part of a regular but informal gathering of scientists in his lab.
"One day they were talking about their work and one of the neurosurgeons said, 'Hey, you know, we have a patient,'" Deisseroth says.
The patient had a form of epilepsy that sometimes caused dissociation. As part of the treatment, doctors had temporarily implanted electrodes in the patient's brain.
That gave Deisseroth's team a way to monitor brain cells in the same area they'd been studying in mice. Once again, they found something important.
"There was a rhythm that appeared, and it appeared only when the patient was dissociating," Deisseroth says.
To confirm their finding, the team delivered pulses of electricity to the areas where they'd seen the rhythm. The patient immediately reported having an out-of-body experience.
The research appears to explain how mammal brains are able to temporarily decouple mind and body, though it's still not clear why they have this ability.
The research also could lead to ways to control dissociation without using drugs. That could eventually help a wide range of patients, Solt says.
"In the operating room we'd love to have a drug like ketamine that just produces the pain-killing properties without having these other psychological manifestations," he says.
Preventing dissociation might also help patients who have certain mental illnesses or who are recovering from a traumatic experience.
But dissociation can be beneficial, Solt says.
For example, ketamine appears to help people with severe depression, in part because it temporarily decouples certain areas of the brain.
"There seems to be this link between dissociation and the anti-depressive effect of ketamine," he says, noting that doses too low to produce even a mildly altered state appear to offer less benefit to people with depression.
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