Taking psychedelics can dissolve the boundary between yourself and the rest of the world, leaving a profound sense of oneness. Now scientists have revealed that specific changes to the brain that may cause this altered sense of consciousness.

The results, published today in Nature, show how taking psilocybin—an active ingredient in magic mushrooms—causes brain networks that typically process the self and the outside world separately to become integrated.

“It reframes our understanding of the psychedelic experience by providing a biological basis for some of the meaning and coherence people report,” says lead author Devon Stoliker, a computational neuroscientist at Monash University in Australia.

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During a psilocybin trip, brain activity becomes more random or chaotic. Networks of neurons that usually fire together become desynchronized, and new connections can form. This shakes up the brain’s existing patterns of connectivity—and that may contribute to its potential therapeutic effect for certain mental health conditions. But the experience is also paradoxical, Stoliker says. “If the brain becomes more disorganized,” he says, “then why do some people have highly meaningful and coherent experiences?”

In the new study, Stoliker and his colleagues found a “hidden order” to this chaos, he says. Curiously, this order emerged in people whose conscious experience had been most strongly altered by psilocybin.

The researchers gave 62 healthy adults with no psychedelic experience a dose of psilocybin, then scanned their brains in varying contexts: resting, meditating and listening to music—all with their eyes closed—and while watching a movie. Many participants experienced a blissful state of oneness, which the researchers call “embeddedness.” One participant reported, “I melded with the MRI machine, floor, walls, air. It was like nothing existed except for me, or me as part of something bigger.”

The researchers measured how synchronized different brain networks were with each other. They found that systems responsible for processing sensory input from the outside world became less connected with the rest of the brain, while those responsible for higher-level processing became more connected.

“Broadly, [this] suggests a shift in the balance between internally generated and sensory processing,” Stoliker says.

Next, the researchers used machine learning to identify patterns hiding in the data. Specifically, they analyzed individual participants’ brain activity while the trip evolved and as they did different tasks. People who had less profound experiences had widely variable brain activity—even if they were engaged in the same activity as their peers. But for people who felt a strong sense of oneness, key dimensions of their brain activity tended to look the same as each other, forming distinct patterns for each activity they performed.

In other words, Stoliker explains, “network activity became more similar when participants experienced less separation between self and world.”

The findings offer a neurobiological explanation for why the context of a psychedelic trip—where and when it happens, or what someone does during it—can so greatly influence the experience.

“Context sensitivity is a double-edged sword,” says Nico Dosenbach, a neurologist at Washington University in Saint Louis, who was not involved in the study. The results highlight the importance of having a “controlled, positive setting, which would make therapy more expensive and difficult to deliver—but not unrealistic,” he says. Computational neuroscientist Adeel Razi, the study's senior author, notes that studying individual brains during a trip using machine learning could help reveal why the same drug produces such different experiences in different people.

Researchers are currently split on whether the apparent benefits of psychedelics stem from the conscious experience of tripping or from the underlying changes in brain connectivity, explains Lorenzo Pasquini, a neuroscientist at the University of California, San Francisco, who wasn’t involved in the study. The new study doesn’t answer that question, he says, but it hints at the importance of people’s conscious experience.

On a more philosophical level, the findings suggest that the division we typically perceive between ourselves and the world is actively managed by the brain, Stoliker says. “Rather than psychedelics simply creating an illusion that the self and world are one,” he says, “they may temporarily reduce the brain processes that normally maintain this separation.”

Perhaps the illusion is not the sense of oneness but our perceived separation between the self and the world to begin with. “Psychedelics may offer a temporary glimpse of a bigger picture,” Stoliker says.