One dose, one month of new brain connections.

THE DISPATCH

In January 2026, a team led by Alex Kwan at Yale published the most detailed picture yet of what a single dose of psilocybin actually does inside the brain in mice: new dendritic spines in a specific frontal cortex network, still measurable a month later.¹ The finding builds on the same lab's original 2021 discovery and adds something new, which specific circuits get rewired, and which don't.¹ ² It's the mechanism underneath nearly everything else this newsletter covers, and it's the same mechanism Rose Hill's own licensed research at Johns Hopkins is now testing in a population far outside psychiatry: chronic stroke survivors.³

In this issue:

→ What the newest mechanism research shows, and how it builds on five years of prior work

→ A veterans study that measured this mechanism directly in brain activity, not just in how people said they felt

→ Where COMP360's regulatory history stands, and where Rose Hill's own stroke trial and other treatments in this space are headed

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THE SCIENCE

In January 2026, Cell published results from Alex Kwan's laboratory at Yale showing that a single dose of psilocybin triggers the formation of new dendritic spines, the tiny structures neurons use to connect to each other, specifically in the mouse dorsal medial frontal cortex, with the increased spine density persisting for at least a month.¹ The effect isn't uniform across the brain. It's network specific: the same dose strengthens the routing of inputs from perceptual and medial brain regions to subcortical targets, while weakening inputs that are part of purely cortico-cortical recurrent loops.¹ This builds directly on the same lab's 2021 finding that psilocybin induces rapid, persistent dendritic spine growth in the frontal cortex. The new work identifies which specific circuits that growth actually rewires.²

This structural change traces back to a more specific molecular story than "psilocybin activates a serotonin receptor." A 2023 Nature Neuroscience study found that psilocin, the active metabolite of psilocybin, and LSD bind directly to TrkB, the BDNF receptor and regulator of neuronal growth and differentiation, with roughly 1,000-fold higher affinity than other antidepressants, and that this TrkB binding drives plasticity and antidepressant-like effects in mice independently of 5-HT2A receptor activation.⁴ The subjective, perceptual effects of these compounds run through a separate pathway, 5-HT2A activation, that doesn't require TrkB binding at all.⁴ In human cortical neurons, psilocin has separately been shown to upregulate BDNF production and drive 5-HT2A receptor internalization, a potential mechanism for why the effect is sustained rather than fading within hours.⁵ Put together, the structural plasticity mechanism and the perceptual experience appear to be two distinct, separable processes rather than one causing the other, part of why researchers are now asking whether a future therapy could someday target the plasticity mechanism without requiring the full subjective experience.

This same mechanism, the reopening of a neuroplastic window rather than a symptom-specific chemical effect, is why Rose Hill's own licensed research is being tested in neurological conditions, somewhere psychiatry doesn't usually go. At Johns Hopkins, researchers Gül Dölen, Steve Zeiler, and John Krakauer are running PHATHOM (Psychedelic Healing: Adjunct Therapy Harnessing Opened Malleability), a Phase 1 trial combining psilocybin with digitally guided physical therapy for chronic stroke survivors.³ As Dölen has put it, "psychedelics have shown remarkable potential to reopen critical periods, and if harnessed correctly, this reopened window of brain malleability could revolutionize stroke rehabilitation."³

The mechanism is the same whether the target is a depressed mood or a stroke-damaged motor circuit. What differs is what the brain is being asked to relearn.

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THE STORY

In a 2025 Frontiers in Psychiatry study, 21 veterans with a history of traumatic brain injury completed psilocybin retreats in Jamaica through the Heroic Hearts Project, and researchers didn't just ask how they felt afterward.⁶ They measured it. EEG recordings taken before and after the retreat showed decreased delta and theta wave activity in the frontal and temporal regions, along with enhanced coherence in the alpha and beta bands, a pattern consistent with improved neural communication.⁶ Reported mental health outcomes improved alongside the brain activity changes, not instead of them. It's the same underlying story as the mechanism research above: something measurable is changing inside the brain, not just how someone describes their mood afterward. For veterans carrying both trauma and physical brain injury, that distinction matters.

Rose Hill Life Sciences is a psychedelic research organization – specializing in the production and research of Psilocybe cubensis operating at the intersection of science and therapeutic integration.

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ON OUR RADAR

① COMP360's Regulatory Head Start The FDA granted Compass Pathways' synthetic psilocybin, COMP360, Breakthrough Therapy Designation for treatment-resistant depression on October 23, 2018, years before this year's Phase 3 results or National Priority Voucher.⁷ Breakthrough Therapy status is granted specifically on early evidence that a drug may offer substantial improvement over existing treatments. Mechanism research like the findings above is part of what continues to support that designation as the drug moves toward a potential approval decision.⁷

② Inside Rose Hill's Own Stroke Trial PHATHOM, Rose Hill's licensed research at Johns Hopkins, pairs a single supported psilocybin session with structured, digitally guided physical therapy and validated motor recovery scales, testing patients with acute, subacute, and chronic stroke.³ It's the first trial to test psilocybin specifically for stroke recovery, pairing a psychedelic session with physical rehabilitation rather than standard psychiatric care.

③ Five Years From Discovery to Precision The 2026 Cell paper documenting which brain circuits get rewired by psilocybin in mice builds directly on a 2021 Neuron paper from the same Yale lab, the first study to show psilocybin induces persistent dendritic spine growth in the living brain at all.² Five years and two major papers later, the mechanism field has moved from establishing that structural rewiring happens to mapping specifically where it happens, a sign of a research area maturing from discovery to precision.

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YOU ASKED

Q: "If a single psilocybin session can measurably change my brain according to this research, why do some people go back to feeling worse again after a few months?"

Because the mechanism reopens a window for change, it doesn't guarantee what fills that window. The dendritic spine growth and network rewiring documented in this research create the conditions for new patterns to take hold, but what actually gets reinforced during that reopened period, through therapy, environment, and ongoing support, appears to matter as much as the dose itself. That's consistent with the 12-month veteran depression data we've covered previously: durable response in a meaningful share of patients, but not all of them, and not permanently for everyone. The honest answer is that this mechanism explains why a single dose can work as well as it does, not why it will work the same way for every person indefinitely.

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This week's takeaway: the newest mechanism research shows a single psilocybin dose creates new, measurable brain connections that persist for at least a month, in specific circuits rather than uniformly across the brain in mice. It's the same structural mechanism Rose Hill's own licensed research is now testing in stroke recovery, a different application built on identical biology.

A question worth sitting with: if the same mechanism can be aimed at a depressed mood or a stroke-damaged motor circuit, what other conditions defined by a loss of neuroplasticity might be worth testing next?

Read the study directly: Cell — Psilocybin Triggers an Activity-Dependent Rewiring of Large-Scale Cortical Networks

The person in your network who needs this most already came to mind while you were reading. Forward it to them.

[— Bryan Smith

PhD, Biologist and Drug Developer

Advancing the development of novel psychedelic-based therapeutics

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FOOTNOTES

¹ Shao, L.-X., et al. "Psilocybin triggers an activity-dependent rewiring of large-scale cortical networks." Cell, 2026. https://www.cell.com/cell/fulltext/S0092-8674(25)01305-4

² Shao, L.-X., et al. "Psilocybin induces rapid and persistent growth of dendritic spines in frontal cortex in vivo." Neuron, 2021. https://www.sciencedirect.com/science/article/pii/S0896627321004232

³ Johns Hopkins Medicine. "PHATHOM: Psychedelic Healing: Adjunct Therapy Harnessing Opened Malleability." Phase 1 trial led by Gül Dölen, Steve Zeiler, and John Krakauer. https://hitconsultant.net/2025/06/04/johns-hopkins-launches-first-psilocybin-trial-for-stroke-recovery/

⁴ Moliner, R., et al. "Psychedelics promote plasticity by directly binding to BDNF receptor TrkB." Nature Neuroscience, 2023. https://www.nature.com/articles/s41593-023-01316-5

⁵ "Psilocin fosters neuroplasticity in iPSC-derived human cortical neurons." eLife, 2024. https://elifesciences.org/articles/104006

⁶ "Improved mental health outcomes and normalised spontaneous EEG activity in veterans reporting a history of traumatic brain injuries following participation in a psilocybin retreat." Frontiers in Psychiatry, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12364870/

⁷ COMPASS Pathways. "COMPASS Pathways receives FDA Breakthrough Therapy designation for psilocybin therapy for treatment-resistant depression." October 23, 2018. https://ir.compasspathways.com/News--Events-/news/news-details/2018/COMPASS-Pathways-receives-FDA-Breakthrough-Therapy-designation-for-psilocybin-therapy-for-treatment-resistant-depression/default.aspx

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