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Neuroplasticity and Psychedelics: a comprehensive examination of classic and non-classic compounds in pre and clinical models

T0 review · 3 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read Psychedelics may achieve rapid and lasting therapeutic effects by opening a short-lived window of heightened neural sensitivity to the environment, then converting that sensitivity into lasting structural change.

desk verdict A careful synthesis of preclinical plasticity evidence that names its own translation gap; the clinical inference remains unproven. read the letter →

arxiv 2411.19840 v1 pith:7H25W3MN submitted 2024-11-29 q-bio.NC q-bio.BM

Claudio Agnorelli , Meg Spriggs , Kate Godfrey , Gabriela Sawicka , Bettina Bohl , Hannah Douglass , Andrea Fagiolini , Hashemi Parastoo
show 3 more authors
Robin Carhart-Harris David Nutt David Erritzoe
This is my paper · ORCID
classification q-bio.NCq-bio.BM
keywords neuroplasticitypsychedelicsmeta-plasticityhyper-plasticitycriticalperiodsBDNF-TrkBsignalingketaminepsilocybin
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Psychedelics stand apart from standard antidepressants because one or a few doses can produce symptom relief that begins quickly and lasts long after the drug has left the body. This review argues that the biological reason is a two-stage plasticity cascade: the drug first opens a short-lived state of meta-plasticity, in which neurons are unusually sensitive to environmental signals, and that state then permits hyper-plastic changes—new dendritic spines, new synapses, and new neurons—that persist for weeks to months. The authors draw the same broad sequence from classic psychedelics (LSD, psilocybin, N,N-DMT, 5-MeO-DMT) and non-classic compounds (ketamine, MDMA) across molecular, structural, and functional levels of evidence. If the sequence is right, the therapeutic work is not done by the drug alone but by what the brain does during a narrow window of opportunity, which gives a biological reason why context and psychotherapy matter. The review is explicit that this model is built mainly on animal data and that direct confirmation in humans is still missing.

What carries the argument

The machinery is the meta-plasticity-to-hyper-plasticity cascade. Meta-plasticity is a change in the threshold for later plasticity; here it appears as a drug-induced, hours-to-days-long window in which neurons are more easily pushed toward change by stimuli, BDNF, and oxytocin. Hyper-plasticity is the resulting structural remodeling—spinogenesis, dendritogenesis, synaptogenesis, and neurogenesis—that outlasts the drug and can persist for weeks to months. Three convergent routes are described: classic psychedelics act through 5-HT2A receptors (including intracellular receptor pools), ketamine blocks NMDA receptors and disinhibits glutamate signaling, and MDMA acts through serotonin and oxytocin pathways; all three converge on the AMPAR–BDNF–TrkB–mTOR signaling system, with direct TrkB binding proposed as a shared meta-plastic trigger. The cascade is what lets a brief drug exposure produce durable change and makes the environment during the window decisive.

What would settle it

A sufficiently powered PET study using the SV2A tracer (a measure of synaptic density) in depressed patients receiving one medium dose of psilocybin, scanned before the dose and again at 24 hours and 2 weeks, would test the translational claim: the model predicts a measurable, baseline-dependent rise in synaptic density in prefrontal cortex and hippocampus, and a failure to see such a rise even in patients with low baseline SV2A would count against it.

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Extended reading notes

Core claim

The central claim is a temporal mechanism: a single therapeutically meaningful dose of a psychedelic creates a limited period of heightened plasticity, and the structural growth that occurs inside that period is what accounts for rapid and enduring clinical effects. In the preclinical evidence, ketamine raises glutamate-evoked spinogenesis in the medial prefrontal cortex for only a few hours before spine density itself rises, and both ketamine and classic psychedelics reopen a critical period for social reward learning in adult mice—ketamine briefly, psilocybin and MDMA for about two weeks, and LSD for about three weeks. The review identifies a convergent molecular core, the AMPAR–BDNF–TrkB–mTOR pathway, entered by classic psychedelics through serotonin 2A receptors and by ketamine through NMDA receptor antagonism, and notes a newer line of evidence that psychedelics and ketamine bind directly to TrkB, sensitizing neurons to BDNF. Human studies so far are limited and mixed, but the authors frame them as early tests of whether the same cascade operates in patients.

Load-bearing premise

The load-bearing premise is that structural and functional plasticity changes seen in rodents—spine growth, critical-period reopening, and LTP/LTD shifts—are causally relevant to how psychedelics relieve psychiatric symptoms in humans, as the review itself notes in the Discussion.

Editorial extensions

If this is right

  • The clinical effect of a psychedelic should be understood as an interaction between the drug and the environment during the post-acute window, not as a drug effect alone.
  • Compound-specific window durations—shortest for ketamine, longest for LSD—imply that adjunctive psychotherapy or brain stimulation should be timed differently for each drug.
  • Structural growth in prefrontal cortex and hippocampus, together with reopening of critical-period plasticity, is proposed as the substrate for reversal of depression- and anxiety-like behaviors and enhanced fear-extinction learning.
  • New PET tracers for synaptic density and non-invasive brain stimulation are proposed as the most promising human tests of whether the same cascade occurs in patients.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the paper's model is right, a decisive clinical prediction follows: a targeted behavioral or learning intervention delivered inside the open window should outperform the same intervention outside it, and the optimal timing should differ between ketamine and LSD.
  • The baseline-dependent SV2A result in the ketamine PET study suggests future human imaging should stratify by baseline synaptic density; group-level null results may otherwise obscure real effects in the patients most likely to benefit.
  • If intracellular 5-HT2A activation is required for dendritogenesis, then membrane permeability may be as important as receptor affinity in drug design, allowing structural plasticity and subjective psychedelic effects to be separated.
  • The same meta-plastic window that consolidates therapeutic learning could consolidate maladaptive learning if the environment is threatening, which would give a neurobiological account of the adverse outcomes the authors mention.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 5 minor

Summary. This review synthesizes preclinical and clinical research on how classic psychedelics (LSD, psilocybin, DMT, 5-MeO-DMT) and non-classic compounds (ketamine, MDMA) affect neuroplasticity. It organizes evidence by structural, functional, and molecular markers, and proposes a two-stage framework: an acute drug-induced state of meta-plasticity (heightened sensitivity to environmental stimuli) that opens a transient window during which hyper-plastic changes (spinogenesis, dendritogenesis, critical-period reopening) become consolidated, with the duration of the window scaling with the subjective duration of the drug. The review is careful to distinguish in vitro, preclinical in vivo, and human data, and it repeatedly flags the translational gap. The central claim of the abstract—that this sequence explains rapid and enduring therapeutic effects in humans—goes beyond what the human evidence currently supports, and the Discussion itself concedes this.

Significance. If the proposed framework is correct, it would reframe psychedelic-assisted therapy as a window of heightened environmental sensitivity rather than a purely pharmacological effect, with direct implications for trial design (timing of psychotherapy, NIBS, and other interventions). The review is valuable as a structured, cross-compound synthesis spanning molecular, structural, and functional levels, and it covers an unusually broad set of primary studies, including recent work on TrkB binding, intracellular 5-HT2AR signaling, and critical-period reopening. Its greatest strength is its explicit attention to the preclinical-to-human translation problem and its candid reporting of null or post-hoc human results, which many earlier reviews have omitted. The paper does not derive any new quantitative claims; its contribution is synthetic and conceptual.

major comments (3)
  1. [Abstract; §6 (Discussion)]
  2. [§3.2.1]
  3. [§4.1.2 and §4.2.2]
minor comments (5)
  1. [General]
  2. [§3.1.1]
  3. [§2]
  4. [§1 and Box 2]
  5. [§5.1.2]

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: this is a literature synthesis whose central claims rest on independent preclinical studies, and the human translation gap is explicitly acknowledged.

full rationale

The paper is a narrative review, not a derivation or prediction exercise, so there is no equation or fitted parameter whose output is equivalent to its input. The organizing framework (acute psychedelic action opens a short meta-plastic window that enables hyper-plastic structural change) is presented as an interpretation of independent animal work, chiefly Ly et al. 2018/2021, Shao et al. 2021, Jefferson et al. 2023, Nardou et al. 2019/2023, Wu et al. 2021, Moliner et al. 2023, and Castrén-group studies. The authors do not claim to have proven this framework in humans; they explicitly write in the Discussion that 'a gap exists in the translation to humans of the working model emerging from the preclinical literature,' and they report null human results (Skosnik et al. 2023, Holmes et al. 2022) rather than suppressing them. Self-citations (Spriggs et al. 2018, Sumner et al. 2020a-c, Lyons et al. 2024, Palmisano et al. 2024) supply methods, one human ketamine LTP data point, one under-review DTI preprint, and a computational follow-up; these are identifiable and are not used as an authority that forbids alternatives. No uniqueness theorem is imported, no ansatz is smuggled in via citation, and the meta-plasticity/hyper-plasticity vocabulary is explicitly sourced to prior work rather than presented as a new first-principles result. The weakest link is evidentiary (rodent-to-human translation), not circular.

Assumptions & free parameters 0 free parameters · 4 assumptions · 0 invented entities

The paper is a review and therefore introduces no free parameters or invented entities. The assumptions listed are the domain assumptions that must hold for its synthesis to be valid: relevance of animal models, validity of imaging and blood biomarkers, and acceptance of standard electrophysiological proxies for plasticity.

assumptions (4)
  • domain assumption Animal models of neuroplasticity (spine density, dendritogenesis, critical period reopening) are relevant models for therapeutic effects in human neuropsychiatric disorders.
    The review's framework links rodent structural and functional changes to clinical outcomes, but the authors themselves state the translational gap is an open problem (Section 6).
  • domain assumption [11C]-UCBJ PET signal reflects synaptic density and is therefore a valid in vivo measure of structural plasticity.
    Used in Sections 3.1.2 and 3.2.1 as evidence of synaptic density; the authors note it is uncertain whether the signal reflects structural or functional plasticity.
  • domain assumption Peripheral blood BDNF levels are a meaningful proxy for central nervous system neuroplasticity.
    The human molecular marker evidence relies on serum and plasma BDNF; the paper acknowledges this is an indirect measure and that results are mixed (Section 5).
  • domain assumption Standard electrophysiological paradigms (LTP, LTD, paired-pulse facilitation, monocular deprivation) are accepted measures of functional plasticity.
    These paradigms are used throughout the functional plasticity sections and are treated as established tools from the cited methods literature.

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Cite this review

Pith. "Pith review of Neuroplasticity and Psychedelics: a comprehensive examination of classic and non-classic compounds in pre and clinical models." pith.science (2026). https://pith.science/paper/7H25W3MN

@misc{pith2026241119840,
  author       = {Pith},
  title        = {Pith review of: Neuroplasticity and Psychedelics: a comprehensive examination of classic and non-classic compounds in pre and clinical models},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/7H25W3MN}},
  note         = {Machine review of arXiv:2411.19840}
}
read the original abstract

Neuroplasticity, the ability of the nervous system to adapt throughout an organism's lifespan, offers potential as both a biomarker and treatment target for neuropsychiatric conditions. Psychedelics, a burgeoning category of drugs, are increasingly prominent in psychiatric research, prompting inquiries into their mechanisms of action. Distinguishing themselves from traditional medications, psychedelics demonstrate rapid and enduring therapeutic effects after a single or few administrations, believed to stem from their neuroplasticity-enhancing properties. This review examines how classic psychedelics (e.g., LSD, psilocybin, N,N-DMT) and non-classic psychedelics (e.g., ketamine, MDMA) influence neuroplasticity. Drawing from preclinical and clinical studies, we explore the molecular, structural, and functional changes triggered by these agents. Animal studies suggest psychedelics induce heightened sensitivity of the nervous system to environmental stimuli (meta-plasticity), re-opening developmental windows for long-term structural changes (hyper-plasticity), with implications for mood and behavior. Translating these findings to humans faces challenges due to limitations in current imaging techniques. Nonetheless, promising new directions for human research are emerging, including the employment of novel positron-emission tomography (PET) radioligands, non-invasive brain stimulation methods, and multimodal approaches. By elucidating the interplay between psychedelics and neuroplasticity, this review informs the development of targeted interventions for neuropsychiatric disorders and advances understanding of psychedelics' therapeutic potential.

Figures

Figures reproduced from arXiv: 2411.19840 by the authors.

Figure 1
Figure 1. Taxonomy of neuroplastic processes. 3.1. Ketamine 3.1.1. Preclinical [PITH_FULL_IMAGE:figures/full_fig_p008_1.png] view at source ↗

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

18 extracted references · 15 canonical work pages

  1. [6]

    In Figure 3, only the results coming from studies investigating the neuroplastic changes induced by a single medium dose of psychedelic compounds are summarised

    Discussion The results presented on the effects of psychedelics on structural, functional, and molecular markers of neuroplasticity demonstrate that these compounds exert a complex and multifaceted impact on neuroplasticity, producing significant long- lasting biological changes in the organism with behavioral correlates and hence implications for human t...

    work page 2022

  2. [14]

    Reduced Dorsal Prefrontal Gray Matter After Chronic Ketamine Use. Biol. Psychiatry 69, 42–48. https://doi.org/10.1016/j.biopsych.2010.08.030 Liao, Y., Tang, J., Ma, M., Wu, Z., Yang, M., Wang, X., Liu, T., Chen, X., Fletcher, P.C., Hao, W., 2010. Frontal white matter abnormalities following chronic ketamine use: a diffusion tensor imaging study. Brain 133...

    work page doi:10.1016/j.biopsych.2010.08.030 2010

  3. [16]

    Rapid and long-lasting antidepressant-like effects of ketamine and their relationship with the expression of brain enzymes, BDNF, and astrocytes. Braz. J. Med. Biol. Res. 54, e10107. https://doi.org/10.1590/1414-431X202010107 Walsh, Z., Mollaahmetoglu, O.M., Rootman, J., Golsof, S., Keeler, J., Marsh, B., Nutt, D.J., Morgan, C.J.A., 2022. Ketamine for the...

    work page arXiv

  4. [48]

    Metaplastic effects of subanesthetic ketamine on CA1 hippocampal function

    https://doi.org/10.1016/j.ejpn.2016.07.007 Izumi, Y., Zorumski, C.F., 2014. Metaplastic effects of subanesthetic ketamine on CA1 hippocampal function. Neuropharmacology 86, 273–281. https://doi.org/10.1016/j.neuropharm.2014.08.002 Jefferson, S.J., Gregg, I., Dibbs, M., Liao, C., Wu, H., Davoudian, P.A., Woodburn, S.C., Wehrle, P.H., Sprouse, J.S., Sherwoo...

    work page arXiv 2016

  5. [198]

    Mechanisms of heterosynaptic metaplasticity

    https://doi.org/10.1007/s12640-016-9615-7 Hulme, S.R., Jones, O.D., Raymond, C.R., Sah, P., Abraham, W.C., 2014. Mechanisms of heterosynaptic metaplasticity. Philos. Trans. R. Soc. B Biol. Sci. 369, 20130148. https://doi.org/10.1098/rstb.2013.0148 Hung, C.-C., Liu, Y.-H., Huang, C.-C., Chou, C.-Y., Chen, C.-M., Duann, J.-R., Li, C.-S.R., Lee, T.S.-H., Lin...

    work page arXiv 2014

  6. [364]

    Serum BDNF levels and the antidepressant effects of electroconvulsive therapy with ketamine anaesthesia: a preliminary study

    https://doi.org/10.1007/s12031-019-01419-4 Zheng, W., Cen, Q., Nie, S., Li, M., Zeng, R., Zhou, S., Cai, D., Jiang, M., Huang, X., 2021a. Serum BDNF levels and the antidepressant effects of electroconvulsive therapy with ketamine anaesthesia: a preliminary study. PeerJ 9, e10699. https://doi.org/10.7717/peerj.10699 Zheng, W., Gu, L., Zhou, Y., Wang, C., L...

    arXiv

  7. [463]

    https://doi.org/10.1016/0306-4522(93)90209-x Li, N., Lee, B., Liu, R.-J., Banasr, M., Dwyer, J.M., Iwata, M., Li, X.-Y., Aghajanian, G., Duman, R.S.,

    work page doi:10.1016/0306-4522(93)90209-x

  8. [660]

    Ketamine Regulates Phosphorylation of CRMP2 To Mediate Dendritic Spine Plasticity

    https://doi.org/10.1124/pr.117.015198 41 Zhang, Z., Zhang, JiFeng, Li, J., Zhang, Jiaqi, Chen, L., Li, Y., Guo, G., 2020. Ketamine Regulates Phosphorylation of CRMP2 To Mediate Dendritic Spine Plasticity. J. Mol. Neurosci. 70, 353–

    work page doi:10.1124/pr.117.015198 2020

Show all 18 references
  1. [874]

    The Nucleus Accumbens and Ketamine Treatment in Major Depressive Disorder

    https://doi.org/10.1007/s00213-013-3304-5 Abdallah, C.G., Jackowski, A., Salas, R., Gupta, S., Sato, J.R., Mao, X., Coplan, J.D., Shungu, D.C., Mathew, S.J., 2017. The Nucleus Accumbens and Ketamine Treatment in Major Depressive Disorder. Neuropsychopharmacology 42, 1739–1746....

    2017

  2. [888]

    Brain-Derived Neurotrophic Factor Val66Met Allele Impairs Basal and Ketamine-Stimulated Synaptogenesis 34 in Prefrontal Cortex

    https://doi.org/10.1080/08941939.2019.1710626 Liu, R.-J., Lee, F.S., Li, X.-Y., Bambico, F., Duman, R.S., Aghajanian, G.K., 2012. Brain-Derived Neurotrophic Factor Val66Met Allele Impairs Basal and Ketamine-Stimulated Synaptogenesis 34 in Prefrontal Cortex. Biol. Psychiatry 71...

    2019

  3. [1187]

    Acute dose-dependent effects of lysergic acid diethylamide in a double-blind placebo-controlled study in healthy subjects

    https://doi.org/10.1038/s41386-022-01297-2 Holze, F., Vizeli, P., Ley, L., Müller, F., Dolder, P., Stocker, M., Duthaler, U., Varghese, N., Eckert, A., Borgwardt, S., Liechti, M.E., 2021. Acute dose-dependent effects of lysergic acid diethylamide in a double-blind placebo-cont...

    2021 doi

  4. [2010]

    Science 329, 959–964

    mTOR-Dependent Synapse Formation Underlies the Rapid Antidepressant Effects of NMDA Antagonists. Science 329, 959–964. https://doi.org/10.1126/science.1190287 Liao, C., Dua, A.N., Wojtasiewicz, C., Liston, C., Kwan, A.C., 2024. Structural neural plasticity evoked by rapid-acti...

    doi

  5. [2011]

    Nature 475, 91–95

    NMDA receptor blockade at rest triggers rapid behavioural antidepressant responses. Nature 475, 91–95. https://doi.org/10.1038/nature10130 Bærentzen, S.L., Waszkiewicz, A.L., Thomsen, M., Knudsen, C., Elfving, B., Landau, A.M., 2024. A single subanaesthetic dose of the rapid-a...

  6. [2012]

    Synaptic potentiation is critical for rapid antidepressant response to ketamine in treatment-resistant major depression. Biol. Psychiatry 72, 555–561. https://doi.org/10.1016/j.biopsych.2012.03.029 Costa, G., Gołembiowska, K., 2022. Neurotoxicity of MDMA: Main effects and mech...

    2012

  7. [2013]

    Different effects of the NMDA receptor antagonists ketamine, MK-801, and memantine on postsynaptic density transcripts and their topography: Role of Homer signaling, and implications for novel antipsychotic and pro-cognitive targets in psychosis. Prog. Neuropsychopharmacol. Bi...

    doi

  8. [2020]

    Neuropsychopharmacology 45, 462–471

    Distinct acute effects of LSD, MDMA, and D-amphetamine in healthy subjects. Neuropsychopharmacology 45, 462–471. https://doi.org/10.1038/s41386-019-0569-3 Huang, H., Liu, C.-M., Sun, J., Hao, T., Xu, C.-M., Wang, D., Wu, Y.-Q., 2016. Ketamine Affects the Neurogenesis of the Hi...

    doi

  9. [2021]

    Cell Rep

    Prolonged epigenomic and synaptic plasticity alterations following single exposure to a psychedelic in mice. Cell Rep. 37, 109836. https://doi.org/10.1016/j.celrep.2021.109836 Debanne, D., Guérineau, N.C., Gähwiler, B.H., Thompson, S.M., 1996. Paired-pulse facilitation and dep...

    2021

  10. [2181]

    Acute Effects of Psilocybin After Escitalopram or Placebo Pretreatment in a Randomized, Double-Blind, Placebo-Controlled, Crossover Study in Healthy Subjects

    https://doi.org/10.1038/s41598-023-49817-4 Becker, A.M., Holze, F., Grandinetti, T., Klaiber, A., Toedtli, V.E., Kolaczynska, K.E., Duthaler, U., Varghese, N., Eckert, A., Grünblatt, E., Liechti, M.E., 2022. Acute Effects of Psilocybin After Escitalopram or Placebo Pretreatmen...

    2022

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