One with the world? A new look at brains transformed by psychedelics.
Ars Technica · LC · trust 45/100
Seeing visions One with the world? A new look at brains transformed by psychedelics. Participants meditated inside an MRI tube, with and without psilocybin.
85 Credit: Tashi-Delek Credit: Tashi-Delek Text settings Story text Size Small Standard Large Width * Standard Wide Links Standard Orange * Subscribers only Learn more Minimize to nav For about a decade, the mainstream understanding has been that psychedelics cause chaos in the brain. Brain networks—the stable patterns of communication that handle vision, attention, or our sense of self, and more—loosen and start talking to each other all at once. EEG traces get noisier and more complex. “Think of the networks of the brain as highways,” says Devon Stoliker, a neuroscientist at Monash University. “Under psychedelics, these highways break down into many different directions.”
In a recent Nature study, Stoliker’s team designed an experiment to test whether these directions are truly chaotic and random. Researchers gathered 62 people who had never taken a psychedelic before, gave them 19 milligrams of psilocybin, a common psychedelic found in certain fungi, and scanned their brains. Then, they used AI to analyze the drugged and sober brain scans. What emerged was not exactly chaos.
Stoliker thinks chaos is not a satisfactory explanation for psychedelics’ effect on the brain. “It never really explained why an individual would have a meaningful experience, why they might have insight, why they might experience clarity, and why these might translate into positive psychological changes,” Stoliker says. To investigate if there are other explanations, he and his colleagues designed a study called PsiConnect.
Volunteers went through the same four-part sequence twice, once sober and once on psilocybin. The sequence included putting participants in four different settings or contexts: eight minutes of lying at rest, a guided meditation, an 11-minute curated music playlist, and finally six minutes of eyes-open video of clouds moving across a sky. Each participant did all four inside an MRI scanner about 80 minutes after dosing, and again on EEG about 150 minutes after.
There were no cognitive tasks researchers routinely go for in brain studies, but there was a purpose behind this omission.
“We wanted ecological validity,” Stoliker says. “We wanted to know what the brain was like when somebody was having an authentic, uninterrupted psychedelic experience. If somebody took a psychedelic in a therapeutic setting, you wouldn’t have them completing tasks.” Stoliker also points out that there’s evidence that giving someone a task mid-trip pulls them out of the state—a phenomenon researchers sometimes call grounding. “Once you introduce these sorts of tasks, you’re actually interrupting the very phenomena you are seeking to measure.” And it worked.
Half of the participants ranked their session among the most meaningful experiences of their lives, and 24 put it in their personal top five. Stolkier and his colleagues started analyzing their brain scan data to find out why.
Measuring global functional connectivity—how much influence each patch of cortex exerts over the rest—the team found that, when participants had their eyes closed, sensory regions lost sway while associative regions gained. “It seems like the brain’s ability to construct reality, or imagination, or our associations, our beliefs, our sense of self—these faculties had more dominance over sensory areas,” Stoliker says, stressing that the interpretation is a hypothetical. “This could help explain why people have meaningful, complex imagery experiences, why they have mystical experiences with imagery that is personally relevant to them.”
Another observation the team made was that connections within each brain network weakened, connections between networks strengthened. The brain’s modularity, a parameter that describes how cleanly neurons stay sorted into specialist teams, dropped across all four parts of the experimental sequence.
What’s more, researchers found that, when sober, activity in a brain with its eyes shut looked very different from a brain watching a movie. Under psilocybin, that difference nearly evaporated. In the visual network, the gap between eyes-open and eyes-closed connectivity shrank by 85 percent. The results from the EEG session independently confirmed that, with alpha-band activity (normally a marker of the brain gating visual input) reduced by nearly half.
“When somebody takes a psychedelic and they’re able to close their eyes and see complex imagery, there seems to be less boundary between the internal and external world than we ordinarily experience,” Stoliker says.
Regardless of these details, the results rather accurately reproduced the chaos in the brain so many researchers claimed psychedelics caused. This chaos, though, turned into order when the team processed their data in a slightly unorthodox way.
Scientists usually do two acts of averaging in a standard brain imaging study. The first is averaging over time. An eight-minute brain scan comprises a few hundred successive images of the whole brain. To understand how two specific regions work together, researchers conventionally average all these images down to a single number describing how well the two regions’ activity matched up across the whole eight minutes.
The problem with this analysis is that it runs the risk of missing ordered structures that appear for a brief period and then disappear into chaos.
The second analysis is averaging over people. Having produced one such number per participant, the standard approach then pools all of them into a group average, on the assumption that individual differences are noise that will be canceled out. Stoliker’s study was focused on individual experiences, so he wanted to avoid that.
Instead, the team fed the moment-by-moment activity of 332 brain regions into CEBRA, a machine-learning tool that compressed the data down to its essential…
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