Psilocybin and Brain Connectivity: The Hyperconnected Brain

Psilocybin & Brain Connectivity

3× more brain disruption than Ritalin

A 2024 Nature study found psilocybin changes brain connectivity more than three times as much as methylphenidate — moving a person's brain about as far from its own baseline as another person's brain already sits.

Siegel et al., Nature, 2024

n=7

adults in Siegel 2024, each scanned roughly 18 times

n=15

volunteers in Lebedev 2015 — ego dissolution tracked via fMRI

59

patients across the two Daws 2022 depression trials

Siegel et al., Nature, 2024

View as image ↗

In 2024, Joshua Siegel and colleagues published a study in Nature that put a number on something the field had only described qualitatively: psilocybin disrupts the brain's connectivity patterns more than three times as powerfully as methylphenidate, the active ingredient in Ritalin.^[6] What makes that figure land is the yardstick the researchers put beside it. Scaled against ordinary day-to-day variation in a person's own brain, methylphenidate scored 1.10 and psilocybin scored 3.52 — and the distance between two different people's brains scored 3.53. For a few hours, the drug moved a person's connectivity about as far from their own baseline as a stranger's brain already sits.

That measurement sits at the center of a decade of fMRI research on psilocybin brain connectivity. The picture that has emerged appears paradoxical at first: psilocybin simultaneously makes the brain more interconnected and less synchronized. These two things are not in contradiction. Understanding how both can be true at the same time is the key to understanding what this compound actually does to a human brain, and why that may matter therapeutically. This article is one in a cluster on psilocybin neuroimaging. For the broader picture of how psilocybin affects the brain's self-referential circuits, see the overview on psilocybin and the default mode network.

What "Hyperconnected" Actually Means — And Why It's Not the Same as More Brain Activity

Psilocybin makes the brain hyperconnected. That phrase gets repeated in science journalism, and it is often misread as "more active overall." The distinction matters, because these are different things.

Brain activity refers to which regions are firing and how intensely. Brain connectivity refers to whether regions are firing in sync with each other. A region can be highly active without coordinating with distant brain areas. Under psilocybin, the more important change is in the coordination pattern, not the raw activity level.

A normal resting brain organizes itself into roughly six major networks. The default mode network handles self-referential thinking, mind-wandering, and rumination. The task-positive network activates when you focus on the outside world. The salience network determines what deserves attention. These networks maintain strong internal coherence — the regions within each network fire together reliably — and relative separation from other networks.

Some networks are actively anti-correlated. When the default mode network is active, the task-positive network suppresses, and vice versa. They operate like a see-saw: one goes up, the other goes down. This organized separation is useful. It allows the brain to switch cleanly between different modes of processing without interference.

Psilocybin disrupts this compartmentalization. Brain regions that belong to separate, normally opposed networks begin firing in tandem. The walls between departments come down, and regions that never normally communicate start broadcasting to each other.

This is what "hyperconnected" means in psilocybin brain connectivity research. It does not describe a brain where everything fires faster. It describes a brain where cross-network communication increases while the tight internal timing of each network loosens.

The implications extend beyond the subjective experience. If rigid network separation is part of what maintains pathological patterns — as in treatment-resistant depression, where the default mode network can loop in self-critical overdrive — then loosening those boundaries may be mechanistically relevant to treatment, not just pharmacologically interesting.

How Carhart-Harris First Mapped the Psychedelic Brain in 2012

The systematic study of psilocybin brain connectivity begins in 2012. Robin Carhart-Harris and colleagues scanned healthy volunteers after administering psilocybin intravenously, using two imaging methods in two separate cohorts of 15 people each — arterial spin labeling to measure cerebral blood flow, and BOLD fMRI to measure changes in venous oxygenation.^[1]

The result overturned a common assumption. Most people expected psilocybin to produce a highly stimulated brain — more activity, more output. What the scanners showed instead was that only decreases were observed in blood flow and BOLD signal, and those decreases were largest in the brain's connector hubs: the thalamus, and the anterior and posterior cingulate cortex.

The quieting tracked the experience directly. The magnitude of the decrease in the anterior cingulate and medial prefrontal cortex predicted the intensity of each person's subjective effects. A follow-up connectivity analysis seeded on the medial prefrontal cortex found that psilocybin significantly decreased its normally positive coupling with the posterior cingulate cortex — two of the default mode network's principal hubs, uncoupling from each other.

This PNAS paper became the foundation on which the entire subsequent field of psilocybin neuroimaging was built. It established the connection between the brain's key connector hubs and the phenomenology of psychedelic experience, and it raised the connectivity questions that would occupy researchers for the next decade.

The 2024 Nature Paper — Psilocybin Is 3× More Disruptive Than Ritalin

In 2024, Siegel and colleagues published the most intensively sampled connectivity analysis of the psychedelic brain state to date, in Nature.^[6]

The anchor study

Siegel et al. (2024) · Nature

Population

7 healthy adults aged 18–45, each with prior psychedelic experience but none in the previous 6 months

Intervention

25 mg oral psilocybin, in a randomized cross-over design with roughly 18 MRI visits per participant

Comparator

40 mg methylphenidate (Ritalin), given in a separate session to the same people

Finding

Psilocybin produced more than threefold greater functional connectivity change than methylphenidate. The change was driven by desynchronization — reduced correlations within networks and reduced anti-correlations between them — and was strongest in the default mode network.

narrow-scope An unusually deep design and an unusually small one: ~18 scans each, but only seven participants, all healthy and all psychedelic-experienced. It characterises the shape and size of the effect far better than its variation across a population.

Siegel et al., Nature, 2024 (NCT04501653)

The comparison was direct: the same participants, the same scanner, two different compounds. Despite psilocybin and methylphenidate causing similar increases in heart rate, psilocybin's effect on functional connectivity was more than threefold larger.

How Big Is the Effect, Really

Psilocybin Moves Your Brain About as Far as Another Person’s Brain Already Is

Siegel and colleagues scaled every condition against ordinary day-to-day variation, set to 1. Methylphenidate, doing a task, and even heavy head motion barely move the needle. Psilocybin lands at 3.52 — and the distance between two different people’s brains is 3.53.

Values are quoted from Siegel and colleagues as reported. This was a precision-imaging design — roughly 18 MRI visits per person, but only seven participants — so it characterises the shape and size of the effect far better than it characterises how it varies across a population.

Siegel et al., Nature, 2024 [6]

The disruption was not random noise. This is the finding that most often gets missed in coverage of this paper. Brain regions with the highest density of 5-HT2A serotonin receptors — the specific receptors that psilocybin activates — showed the most desynchronization, a spatial correspondence the researchers confirmed against receptor-binding maps. The effect was strongest in the default mode network, the circuit tied to the sense of space, time and self.

Two further findings deserve more attention than they usually get. First, the effect was state-dependent: when participants performed a simple auditory–visual matching task in the scanner, the psilocybin-driven disruption significantly decreased. Directing attention outward partially restored normal network structure while the drug was still active. Second, one change outlasted the acute experience — connectivity between the anterior hippocampus and the default mode network remained reduced for weeks after the session. The authors propose that persistent reduction as a candidate correlate of psilocybin's lasting effects.

One widely repeated claim about this paper is worth correcting, because it inverts what the researchers actually reported. It is often said that everyone's brain on psilocybin looks alike — that the psychedelic state has a shared signature identifiable from a scan. Siegel's emphasis runs the other way. The design was built specifically to track individual-specific changes, the analysis found that variability between people in their psilocybin response reflected genuine differences in drug effect rather than measurement error, and individual differences in connectivity change were strongly linked to differences in the subjective experience. The dimension of experience that correlated most strongly with brain change was transcendence — the loss of the usual sense of time or space. What the study established is that the effect is large, not that it is uniform.

For a visual representation of what these connectivity patterns look like across the whole brain, see the connectome on psilocybin: visual maps of a changed brain.

The Apparent Contradiction — Hyperconnected and Desynchronized Are Both True

Read Siegel 2024 and Mortaheb 2024 together and an apparent contradiction emerges.^[5][6] Siegel describes psilocybin as desynchronizing the brain. Mortaheb describes psilocybin as producing hyperconnectivity. Both papers study the same drug and the same class of fMRI measurements. Both findings are real. How can a brain be both at once?

The answer lies in a framework Carhart-Harris proposed in 2014: the entropic brain theory.^[2] The core idea is that psychedelics increase neural entropy — the brain's overall level of disorder and unpredictability. A high-entropy brain has loosened its predictive patterns. It fires less like a machine executing a program and more like a system exploring its own range of possible states.

Desynchronization and hyperconnectivity are two manifestations of the same entropy increase, observed at different scales.

Resolving the Contradiction

Desynchronized and Hyperconnected Are the Same Event at Two Zoom Levels

One paper says psilocybin desynchronizes the brain. Another says it makes the brain hyperconnected. Neither is wrong. They are measuring at different scales, and one change produces both readings.

This is a scale-and-direction diagram, not a measurement. Node positions and blob sizes are illustrative; the only claims being made are the direction of each change and the scale at which it is observed.

Siegel 2024 [6]; Mortaheb 2024 [5]; entropic brain framework [2]

At the small scale, within individual networks, psilocybin reduces the predictable synchrony between regions that normally fire in tight coordination. The internal coherence of each network loosens. This is what Siegel measured as desynchronization.

At the large scale, across entire networks, the same loosening removes a constraint. The anti-correlation that held two networks apart weakens along with the correlation that held each one together, so the statistical distinction between "inside this network" and "outside it" fades. This is what Mortaheb measured as hyperconnectivity.

Neither finding is wrong. Both describe the same brain state. The seeming contradiction resolves once you ask: desynchronized at what scale? Hyperconnected at what scale? The answers are different, and both are real. For a full treatment of the entropy framework, see the entropic brain theory: Carhart-Harris's framework and how psilocybin increases brain entropy.

When Normally Opposed Networks Start Talking — And What Ego Dissolution Actually Tracks

Two claims usually get merged at this point in the story, and separating them matters.

The first claim is about network boundaries, and it is well supported. The default mode network and the task-positive network are normally anti-correlated — the see-saw described earlier. Siegel's central measurement is that psilocybin reduces the correlations within networks and the anti-correlations between them at the same time, which is precisely what "dissolving network distinctions" means.^[6] Nothing new is wired together. The arithmetic that made the networks separate simply stops holding.

The second claim is about what ego dissolution tracks — and here the popular shorthand ("the networks merge, so the self dissolves") does not match the study most often cited for it. Lebedev and colleagues examined this directly in 2015 with 15 healthy volunteers in a placebo-controlled design, comparing intravenous saline against 2 mg of intravenous psilocybin.^[3] Ego dissolution was scored as the first principal component of 22 visual analogue ratings collected after scanning.

What predicted ego dissolution was more specific than two big networks merging:

• Decoupling between the medial temporal lobe and high-level cortical regions — the strongest association in the analysis.
• "Disintegration" of the salience network — the system that decides what deserves attention losing its internal coherence.
• Reduced communication between the hemispheres.

The study also found a baseline predictor, which is easy to overlook and genuinely interesting: people whose executive network nodes showed lower diversity before dosing were more likely to experience ego dissolution under psilocybin. Some of the response was written into the brain's resting architecture before the drug was given.

For the full story of how psilocybin physically disables the brain's normal gating systems to produce this cross-network communication, see how psilocybin makes brain regions talk to each other.

Why the Hyperconnected State Feels Like Unity

Psilocybin produces a range of effects: altered visual perception, emotional amplification, distorted time, ego dissolution, and a sense of deep interconnectedness that many describe as unity or oceanic boundlessness. A reasonable question is which aspects of the experience are driven by which brain changes.

Mortaheb and colleagues addressed this in 2024 using ultra-high-field 7T imaging.^[5] Healthy participants were randomized to receive psilocybin (n=22) or placebo (n=27) and scanned for six minutes in an eyes-open resting state at the peak of the drug effect, 102 minutes after dosing. Subjective experience was captured with the 5-Dimensional Altered States of Consciousness scale, administered six hours after intake.

Psilocybin produced alterations across all dimensions of that scale, alongside widespread increases in average functional connectivity. The time-varying analysis then found something more specific: a recurrent hyperconnected pattern, characterised by low BOLD signal amplitude, that the brain kept returning to.

The link to experience was ranked rather than exclusive. Higher probability of transitioning into that hyperconnected pattern was associated first with oceanic boundlessness — the mystical sense of unity and selflessness — and second with visionary restructuralization, the dimension that covers visual and perceptual alteration. The paper's own title says "primarily associated with oceanic boundlessness," and primarily is the right word. It is not the case that hyperconnectivity tracks mystical experience and has nothing to do with visual effects; the mystical dimension simply led.

That ranking still matters for a practical reason. Multiple clinical studies have reported that the mystical quality of a psilocybin experience predicts therapeutic outcomes, particularly in depression, addiction, and end-of-life anxiety. If that mystical quality is the experiential dimension most closely tied to the hyperconnected state, then hyperconnectivity is unlikely to be an incidental feature of the psilocybin state. It becomes a reasonable candidate for the brain mechanism underlying the therapeutically relevant component of the experience — a candidate, not a demonstrated cause.

From Brain State to Clinical Outcome — The Daws 2022 Connection

The connectivity findings would be scientifically compelling and clinically irrelevant without a demonstrated connection to patient outcomes. That connection was established by Daws and colleagues in a 2022 paper in Nature Medicine, which pooled brain imaging across two depression trials totalling 59 patients.^[4]

The two trials were deliberately different in design, and the distinction carries most of the weight of the result:

The central finding held in both: psilocybin therapy decreased brain network modularity — meaning separate networks communicated more across their normal boundaries — and the size of that decrease correlated with how much a patient's depression improved. Network cartography showed that 5-HT2A-rich higher-order networks became more interconnected and more flexible after treatment.

Escitalopram produced a milder antidepressant response and no comparable changes in brain network organization at all.

What the Chain Actually Rests On

Three Links From Brain Change to Clinical Benefit — and What Holds Each One Up

The therapeutic story depends on a chain, not a single result. Each link comes from a different study with a different design and sample size. Laid out with the real numbers, it is clear which end is solid and which end is still thin.

Siegel 2024 [6]; Mortaheb 2024 [5]; Daws 2022 [4]

This is the finding that most sharply separates psilocybin from conventional antidepressants at the mechanistic level. Standard antidepressants increase the availability of serotonin throughout the brain; they change mood chemistry. In the Daws analysis, they did not reorganize the brain's network structure. Psilocybin did.

Two caveats keep this from being more than it is. The frequently quoted "predicts response at six months" result comes from Trial 1 only — the open-label arm with 16 imaged patients and no control group, the weakest of the two designs. And whether network reorganization causes the antidepressant response, or is a correlated marker of a deeper process, remains genuinely unresolved.

For a detailed look at what brain integration means, how it is measured, and what the full body of integration research shows, see psilocybin and global brain connectivity: from segregation to integration.

What the Connectivity Research Still Cannot Tell Us

The evidence is genuinely compelling. It is also worth being explicit about where the limits are.

Sample sizes are small. The Siegel 2024 Nature paper studied seven participants, all healthy and all with prior psychedelic experience. Carhart-Harris's foundational 2012 PNAS work used two separate cohorts of 15. Mortaheb scanned 22 people on psilocybin. Daws imaged 16 patients in one trial and 22 in the other. These are sufficient to establish that real, consistent effects exist and to characterize their general shape. They are not large enough to establish how these effects vary across individuals, across doses, across different mental health conditions, or across different fMRI analysis methods. The field is building on a narrow empirical base — and in Siegel's case, on a deliberately deep-but-narrow one.

The correlation-to-causation gap has not been closed. Daws 2022 showed that connectivity integration tracks antidepressant response. It did not show that the connectivity change causes it. Both might be downstream of a third factor: changes in 5-HT2A receptor signalling after the session, neuroplastic growth in dendritic spine density, the quality of psychological integration during the therapy weeks, or something else entirely. The connectivity changes are real and trackable. Whether they are the active therapeutic ingredient or an accompanying signature is genuinely unknown.

Persistence is partly measured and partly not. It is sometimes said that no one has looked past the acute experience, and that is no longer accurate — Siegel tracked participants for three weeks and found the hippocampal–default mode network decoupling persisted. But that was seven healthy volunteers, not patients in treatment, and it is a long way from showing that a durable connectivity change underlies durable clinical benefit. If lasting benefit depends on connectivity changes that persist, those changes still need to be measured in patients, months out. If instead the benefit comes from an acute disruption that resets a rigid system — with the brain then finding a new stable configuration on its own — the acute changes would be therapeutically relevant even without persistence. These are different mechanistic stories, and the data does not yet distinguish between them. For the full body of fMRI evidence across studies and methodologies, see functional connectivity changes under psilocybin: fMRI evidence.

How to read this research

Moderate

These are brain-imaging findings, not a treatment protocol

Concern

Every study described here administered psilocybin in a controlled research setting: screened participants, known doses of pharmaceutical-grade compound, medical monitoring, and — in the depression trials — structured psychological support before, during and after dosing. The connectivity changes were measured under those conditions. Psilocybin remains a Schedule I controlled substance under US federal law and is illegal in most jurisdictions outside specific regulated or research settings.

What the research says

The honest summary of this literature is mechanistic, not clinical: psilocybin reliably and substantially changes brain network organisation, and the size of that change tracks both subjective experience and, in two small depression trials, symptom improvement. That is a reason to take the research programme seriously. It is not evidence that unsupervised use reproduces those outcomes, and none of these studies tested that.

Particularly relevant for: People with a personal or family history of psychosis or bipolar disorder were excluded from these trials, as were people taking a range of psychiatric medications. Siegel's participants were healthy adults with prior psychedelic experience.

What to do

Treat this article as an explanation of what researchers have measured. Anyone considering psilocybin in relation to a diagnosed condition should raise it with a clinician who knows their history and medication list.

Siegel et al., Nature, 2024 (NCT04501653); Daws et al., Nature Medicine, 2022 (NCT03429075)

This article reports research findings and is general information, not medical advice. It does not recommend psilocybin use, and nothing here should be read as guidance for treating depression or any other condition.

The Bottom Line

Psilocybin produces a connectivity state unlike any other compound studied alongside it: more than three times more disruptive than methylphenidate, and characterized by both desynchronization within networks and increased communication between them. The apparent paradox resolves cleanly through the entropic brain framework — both phenomena are real, observed at different scales. Twelve years of fMRI research has built a chain from connectivity changes to subjective experience to clinical outcomes, with greater brain integration tracking greater depression improvement across two trials totalling 59 patients. The evidence is robust enough to take seriously, and the honest caveats are substantial: samples in the single and double digits, every link in the chain correlational rather than causal, and the headline six-month result resting on an open-label trial of 16 patients.

Frequently Asked Questions

What does psilocybin do to brain connectivity?

Psilocybin breaks down the normal compartmentalization between the brain's major networks, allowing regions that rarely communicate to begin cross-talking. In fMRI studies this appears as increased connectivity between networks alongside decreased synchrony within individual networks — the two happen together, because psilocybin reduces both the correlations inside a network and the anti-correlations that hold networks apart. A 2024 Nature study measured this change as more than threefold larger than the change produced by methylphenidate at the doses tested.

Why does psilocybin make the brain hyperconnected?

Psilocybin activates 5-HT2A serotonin receptors concentrated in the higher-order thinking areas of the cortex, and the regions richest in those receptors show the most desynchronization. When a network's internal coherence loosens, the statistical boundary separating it from other networks weakens too, so regions that were segregated stop being segregated. The entropic brain theory (Carhart-Harris, 2014) frames this as an increase in neural entropy: a loosening of the brain's predictive, script-following patterns.

What happens to brain networks during a psilocybin experience?

The brain's normally separated networks begin communicating across their boundaries as the anti-correlations between them weaken. As for the felt sense of the self dissolving, a 2015 placebo-controlled study of 15 volunteers found it tracked something more specific than networks merging: decoupling between the medial temporal lobe and high-level cortex, breakdown of the salience network, and reduced communication between the hemispheres. That study also found people with less diverse executive-network organisation at baseline were more likely to experience ego dissolution.

What does a psychedelic brain look like on an fMRI?

On fMRI, the psilocybin brain shows reduced coherence within normal resting-state networks and increased connectivity between them. The magnitude is striking: in the 2024 Nature study, scaled against ordinary day-to-day variation set at 1, psilocybin scored 3.52 while the difference between two different people's brains scored 3.53. That is a statement about how large the change is, not evidence that everyone's brain on psilocybin looks the same — the same study emphasised individual-specific changes, and found that differences between people in how much their connectivity shifted tracked differences in what they experienced.

Does psilocybin permanently change brain connectivity?

Most of the acute connectivity changes resolve as psilocybin clears the system, but not all of them. The 2024 Nature study tracked participants for three weeks and found reduced connectivity between the anterior hippocampus and the default mode network persisted over that period. Whether that kind of persistence explains lasting clinical benefit is unresolved: the Daws 2022 study showed antidepressant benefit tracking the size of network integration change, but it did not establish that the connectivity change itself endures in patients, or that it causes the benefit. The durability of connectivity change and the durability of clinical benefit are separate questions that have not yet been disentangled.

Sources & References

1. 1RTHM-00245·Carhart-Harris, Robin L et al. (2012). “Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin..” Proceedings of the National Academy of Sciences of the United States of America.Study breakdown →PubMed →↩
2. 2RTHM-00579·Carhart-Harris, Robin L et al. (2014). “The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs..” Frontiers in human neuroscience.Study breakdown →PubMed →↩
3. 3RTHM-00706·Lebedev, Alexander V et al. (2015). “Finding the self by losing the self: Neural correlates of ego-dissolution under psilocybin..” Human brain mapping.Study breakdown →PubMed →↩
4. 4RTHM-00752·Daws, Richard E et al. (2022). “Increased global integration in the brain after psilocybin therapy for depression..” Nature medicine.Study breakdown →PubMed →↩
5. 5RTHM-01951·Mortaheb, Sepehr et al. (2024). “Dynamic Functional Hyperconnectivity After Psilocybin Intake Is Primarily Associated With Oceanic Boundlessness..” Biological psychiatry. Cognitive neuroscience and neuroimaging.Study breakdown →PubMed →↩
6. 6RTHM-00911·Siegel, Joshua S et al. (2024). “Psilocybin desynchronizes the human brain..” Nature.Study breakdown →PubMed →↩