When a person on psilocybin closes their eyes, the gap between what their visual system does and what it does while watching a video shrinks by 85 percent. That single figure, from a new study in Nature, is the cleanest expression of what the drug does to the brain’s usual bookkeeping — and of what brain imaging has been missing about it for a decade.
The accepted account, as Jacek Krywko writes for Ars Technica, has been that psychedelics induce chaos: the stable brain networks that handle vision, attention and the sense of self loosen and start talking to each other all at once, and EEG traces get noisier. “Think of the networks of the brain as highways,” says Devon Stoliker, the Monash University neuroscientist who led the work. “Under psychedelics, these highways break down into many different directions.” Stoliker’s objection was that chaos explains nothing about why the experience is meaningful: “It never really explained why an individual would have a meaningful experience, why they might have insight, why they might experience clarity.”
His team’s study, PsiConnect, recruited 62 people who had never taken a psychedelic and gave them 19 milligrams of psilocybin. Each volunteer ran the same four-part sequence twice, sober and dosed: eight minutes at rest, a guided meditation, an 11-minute curated music playlist, and six minutes of eyes-open video of clouds crossing a sky. All four ran inside an MRI scanner about 80 minutes after dosing, and again on EEG about 70 minutes after that. Deliberately, there were no cognitive tasks. “We wanted ecological validity,” Stoliker says. “Once you introduce these sorts of tasks, you’re actually interrupting the very phenomena you are seeking to measure” — a pull-out effect researchers call grounding. It worked as an experience: half the participants ranked the session among the most meaningful of their lives, and 24 of the 62 put it in their personal top five.
The standard metrics confirm the standard story
Run through conventional analysis, the scans reproduced the chaos picture. Measuring global functional connectivity — how much influence each patch of cortex exerts over the rest — the team found that with eyes closed, sensory regions lost sway while associative regions gained. Connections inside each network weakened while connections between networks strengthened, and modularity, the parameter describing how cleanly neurons stay sorted into specialist teams, dropped across all four contexts. Sober, an eyes-closed brain looks very different from a movie-watching brain; under psilocybin that difference nearly vanished, with the 85 percent contraction in the visual network confirmed independently by the EEG session, where alpha-band activity — normally a marker of gating visual input — fell by almost half. Stoliker’s reading of the associative-region dominance is explicitly a hypothesis: it could explain why the imagery feels personally relevant and mystical.
Two averagings the standard analysis runs
Standard fMRI analysis averages twice. First over time: an eight-minute scan is a few hundred whole-brain images, collapsed into one number per pair of regions describing how well their activity matched across all eight minutes — which erases any ordered structure that appears briefly and dissolves. Then over people: one number per participant, pooled into a group average on the assumption that individual differences are noise. For a study about individual experience, both averages were the enemy. The team’s pipeline instead ran: 332 regional time series per participant, fed moment by moment into CEBRA-Time, a contrastive machine-learning tool, and compressed into a three-dimensional latent trajectory — one point per instant of the scan, order of events preserved, no averaging anywhere.
The trajectories did what the chaos account says they should not. “When they’re not under psilocybin, the brain activity is less differentiated by context,” Stoliker says. “But under psilocybin, we see that the activity becomes organized across time and more clearly differentiated by context.” The dosed trajectories separated into four distinct clusters — rest, meditation, music, movie — cleanly enough that a classifier could read a single moment of brain activity and name the context the person was in. And the classifier’s accuracy scaled with how profound the participant said the experience was: the more structured the brain, the deeper the trip.
Where the effect lives
To assign credit anatomically, the team swapped one network’s psilocybin activity for its sober version and measured how much the classifier degraded. Two networks each accounted for over 20 percent of the effect: the visual network and the default mode network. “The default mode network is strongly associated with the sense of self: daydreaming, mind wandering, thinking about yourself. It’s often been called the narrative self,” Stoliker explains. Under the drug, the two became less differentiated, which the team links to participants’ reports of self and world blurring together — a state they call embeddedness. “Theoretically, we could suggest that psychedelics are temporarily altering the organization of brain networks that ordinarily help maintain this separation that we experience,” Stoliker says. Note the qualifier: the anatomy is measured, the meaning is an interpretation.
The day after dosing, participants rated shifts in connection to themselves, to others and to nature, plus peace, acceptance and creativity, on scales from –100 to 100. “For the vast majority of our participants, we found they had positive psychological changes the next day,” Stoliker says, and the classifier’s context-discrimination performance tracked the size of those shifts. The therapeutic pitch follows directly: if the room, the playlist and the instructions mechanically shape brain organization rather than just setting mood, they become clinical variables that can be tuned. The caveats are also direct. Two people reporting identical embeddedness scores can be having very different subjective experiences, and all 62 volunteers were healthy — not patients with the psychiatric conditions any psilocybin therapy would target.
Monash describes the five-year study as the world’s largest single-site brain-imaging study of acute psilocybin effects, a size claim that comes from the team itself. The result it must defend is narrower and more interesting: that the psychedelic brain is not disordered but reordered — organized by context more sharply than the sober one. Whether that reordering can be deliberately steered, and whether it survives in a patient cohort, is the measurement the field owes next.