The Subjective Effects of Psychedelics May Not Be Necessary for Their Enduring Therapeutic Effects

Knowing and being known: Psychedelic-assisted psychotherapy and the sense of authenticity

Participants in MDMA- and psychedelic-assisted psychotherapy often emerge from these treatments with new beliefs about themselves and the world. Studies have linked changed beliefs with mystical experiences reported by some participants during drug sessions. While there has been some debate about the epistemic value of drug-induced mystical experiences, and about the need for consent to treatments that may alter metaphysical beliefs, less attention has been given to the sense of authenticity that attends these experiences. In this paper, I consider the intersubjective context in which these changed beliefs arise. I suggest that the sense of authenticity people experience with MDMA- and psychedelic-assisted psychotherapy derives from a simultaneous feeling of knowing and being known. The medications used in these treatments reduce the defensive barriers which ordinarily prevent powerful feelings from being intersubjectively shared, allowing the subject to experience knowing and being known with the therapist and/or internalized or imagined others. In explaining this thesis, I discuss Ratcliffe's "existential feeling;" ipseity in incipient psychosis and psychedelic states; Winnicott's notions of the True Self, omnipotence, creativity, and transitional phenomena; implicit relational knowing and moments of meeting; infant-mother dyad research; predictive processing and the relaxed beliefs model of psychedelic action; the role of the "partner in thought" in knowing and feeling known. I propose that a "transitional space" model of MDMA- and psychedelic-assisted psychotherapy is well-suited for working through "not-me" or dissociated experience.

Administration of N,N-dimethyltryptamine (DMT) in psychedelic therapeutics and research and the study of endogenous DMT

As with all drugs, the route, form, and/or dose of a substance administered or applied can play a defining role in its overall pharmacology and use as a therapeutic. This review will focus on these factors as they relate to the psychedelic N,N-dimethyltryptamine (DMT). It will examine the positive and negative aspects of different formulations and routes of administration of DMT and the observed effects from such administrations in the form of ayahuasca teas; oral "pharmahuasca"; injections by intravenous (IV) and intramuscular (IM) routes; inhalation, insufflation; and other routes; and high-dose, low-dose, and "micro-dose" effects. The review will consider possible oral route of administration alternatives that would not require concomitant use of a monoamine oxidase inhibitor. The review will then address the current research findings for DMT from in vivo and in vitro studies as well as the possibility that these findings may be revealing the role of endogenous DMT in normal brain function.

Assessing the effects of methodological differences on outcomes in the use of psychedelics in the treatment of anxiety and depressive disorders: A systematic review and meta-analysis

BACKGROUND

Classical psychedelics are a group of drugs which act as agonists on the serotonin-2A (5-HT2A) receptor. Evidence suggests they may have a uniquely rapid and enduring positive effect on mood. However, marked heterogeneity between methodological designs in this emerging field remains a significant concern.

AIMS

To determine how differences in the type of psychedelic agent used and the number of dosing sessions administered affect subjects' depression and anxiety outcomes and adverse drug reactions (ADR).

METHODS

This review collected and screened 1591 records from the MEDLINE and Web of Science databases for clinical trials reporting objective data on mood for subjects with a known anxiety or depression.

RESULTS

After screening, nine clinical trials met inclusion criteria. Meta-analysis of these studies showed significant, large positive effect sizes for measures of anxiety (Cohen's d = 1.26) and depression (Cohen's d = 1.38) overall. These positive effects were also significant at acute (⩽1 week) and extended (>1 week) time points. No significant differences were observed between trials using different psychedelic agents (psilocybin, ayahuasca or lysergic acid diethylamide (LSD)), however, a significant difference was observed in favour of trials with multiple dosing sessions. No serious ADR were reported.

CONCLUSION

Psilocybin, ayahuasca and LSD all appear to be effective and relatively safe agents capable of producing rapid and sustained improvements in anxiety and depression. Moreover, the findings of the present analysis suggest that they may show a greater efficacy when given to patients over multiple sessions as compared to the more common single session used in many of the existing trials.

Decreases in State and Trait Anxiety Post-psilocybin: A Naturalistic, Observational Study Among Retreat Attendees

Anxiety disorders are the most common type of psychiatric disorders among Western countries. Evidence-based treatment modalities including pharmacological and cognitive-behavioral therapy result in deficient treatment responses. Historical and recent research suggests psychedelic drugs may be efficacious in alleviating anxiety-related symptoms among healthy and clinical populations. The main aim of the present study was investigation of the effects of psilocybin-containing truffles, when taken in a supportive group setting, on ratings of state and trait anxiety across self-reported healthy volunteers. Attendees of psilocybin ceremonies were asked to complete a test battery at three separate occasions: before the ceremony (baseline), the morning after, and 1 week after the ceremony. The test battery included questionnaires assessing state and trait anxiety (State-Trait Anxiety Inventory), mindfulness capacities (Five Facet Mindfulness Questionnaire), and personality (Big Five Inventory). Additionally, the psychedelic experience was quantified with the Persisting Effects Questionnaire and the Ego Dissolution Inventory. The total amount of psilocybin-containing truffles consumed by each participant was recorded, and a sample of the truffles was analyzed to determine psilocin concentrations. Fifty-two attendees (males = 25; females = 25; others = 2) completed parts of the baseline assessment, 46 (males = 21; females = 24; others = 1) completed assessments the morning after the ceremony, and 23 (males = 10; females = 13) completed assessments at the 1-week follow-up. Average psilocin consumption across individuals was 27.1 mg. The morning after the ceremony, we observed medium reductions in anxiety measures (both state and trait) compared to baseline ( d ¯ = 6.4; p < 0.001 and d ¯ = 6; p = 0.014, respectively), which persisted over a 1-week period post-ceremony ( d ¯ = 6.7; p = 0.001 and d ¯ = 8.6; p = 0.004, respectively). At 1 week post-ceremony, the non-judging facet of the mindfulness scale was increased ( d ¯ = 1.5; p = 0.03), while the personality trait neuroticism decreased ( d ¯ = 5.2; p = 0.005), when compared to baseline. Additionally, we found ratings of ego dissolution (mean: 59.7, SD: 28.3) and changes in neuroticism to be the strongest predictors of reductions in state and trait anxiety, respectively. In sum, results suggest rapid and persisting (up to 1 week) anxiolytic effects in individuals with sub-clinical anxiety symptoms, which are related to the acute experience of ego dissolution, as well as lasting changes in trait neuroticism. Results also add support to the feasibility and potential efficacy of group sessions with psychedelics. To understand whether these effects extend to wider populations suffering from heightened anxiety, and the mechanisms involved, further experimental research is needed.

Psychedelics, Mystical Experience, and Therapeutic Efficacy: A Systematic Review

The mystical experience is a potential psychological mechanism to influence outcome in psychedelic therapy. It includes features such as oceanic boundlessness, ego dissolution, and universal interconnectedness, which have been closely linked to both symptom reduction and improved quality of life. In this review, 12 studies of psychedelic therapy utilizing psilocybin, ayahuasca, or ketamine were analyzed for association between mystical experience and symptom reduction, in areas as diverse as cancer-related distress, substance use disorder, and depressive disorders to include treatment-resistant. Ten of the twelve established a significant association of correlation, mediation, and/or prediction. A majority of the studies are limited, however, by their small sample size and lack of diversity (gender, ethnic, racial, educational, and socioeconomic), common in this newly re-emerging field. Further, 6 out of 12 studies were open-label in design and therefore susceptible to bias. Future studies of this nature should consider a larger sample size with greater diversity and thus representation by use of randomized design. More in-depth exploration into the nature of mystical experience is needed, including predictors of intensity, in order to maximize its positive effects on treatment outcome benefits and minimize concomitant anxiety. Systematic Review Registration: PROSPERO, identifier CRD42021261752.

How to account for hallucinations in the interpretation of the antidepressant effects of psychedelics: a translational framework

RATIONALE

Recent trials with psychedelics in major depressive disorder and treatment-resistant depression showed remarkable improvements in depressive symptoms that can last for up to several months after even a single administration. The lack of an appropriate placebo control group-as patients are often able to discriminate the subjective effects of the drug-and an incomplete understanding of the role of the hallucinogenic and mystical experience, hampers the interpretation of these therapeutic effects.

OBJECTIVES

To control for these factors, we developed a translational framework based on establishing pharmacokinetic/pharmacodynamic (PK/PD) relationships in rodents and humans for hallucinogenic (i.e., discriminative stimulus effects in rodents and humans; head twitch responses in rodents; questionnaires in humans) and therapeutic effects. For the latter, we selected the pattern separation and attentional set-shifting tasks as measures for cognitive flexibility because of their high translational value. We predict that these PK/PD analyses will lead to a more objective evaluation of improvements in patients compared to relying only on the currently used self-reported questionnaires. We hypothesize that-if the role of the hallucinogenic experience is not central in the antidepressant effects of psychedelics-the ED₅₀'s for the therapeutic effects will be significantly lower than for the hallucinogenic and mystical effects.

CONCLUSION

Our framework will help to inform future studies that aim at the elucidation of the mechanism(s) of action of psychedelics in depression, and the role of the acute subjective and/or hallucinogenic experience in their effects.

Psychedelic Therapy's Transdiagnostic Effects: A Research Domain Criteria (RDoC) Perspective

Accumulating clinical evidence shows that psychedelic therapy, by synergistically combining psychopharmacology and psychological support, offers a promising transdiagnostic treatment strategy for a range of disorders with restricted and/or maladaptive habitual patterns of emotion, cognition and behavior, notably, depression (MDD), treatment resistant depression (TRD) and addiction disorders, but perhaps also anxiety disorders, obsessive-compulsive disorder (OCD), Post-Traumatic Stress Disorder (PTSD) and eating disorders. Despite the emergent transdiagnostic evidence, the specific clinical dimensions that psychedelics are efficacious for, and associated underlying neurobiological pathways, remain to be well-characterized. To this end, this review focuses on pre-clinical and clinical evidence of the acute and sustained therapeutic potential of psychedelic therapy in the context of a transdiagnostic dimensional systems framework. Focusing on the Research Domain Criteria (RDoC) as a template, we will describe the multimodal mechanisms underlying the transdiagnostic therapeutic effects of psychedelic therapy, traversing molecular, cellular and network levels. These levels will be mapped to the RDoC constructs of negative and positive valence systems, arousal regulation, social processing, cognitive and sensorimotor systems. In summarizing this literature and framing it transdiagnostically, we hope we can assist the field in moving toward a mechanistic understanding of how psychedelics work for patients and eventually toward a precise-personalized psychedelic therapy paradigm.

Psychedelic Epistemology: William James and the “Noetic Quality” of Mystical Experience

William James proposed in 1902 that states of mystical experience, central to his idea of religious experience, can be identified based on their ineffability and their noetic quality. The epistemological category of the noetic quality, modified by W. T. Stace in 1960, plays a central but somewhat confounding role in today’s biomedical research involving psychedelic drugs such as psilocybin and LSD. Using scales based on James, it can be shown that psychedelics “reliably occasion” intense subjective states of experience or mystical states. It is debated whether these states are necessary for the wide range of possible mental health therapeutic benefits that appear to follow. This paper reviews what James said about the noetic quality and its relationship to religious experience, epistemology, and states of mystical experience. It explores how the noetic quality is measured in today’s research, addressing a growing list of concerns that psychedelic science can be epistemologically biased, that it is hostile to atheistic or physicalist views, that it injects religion unduly into science, or that it needs to find ways to eliminate the mystical element, if not the entire intense subjective experience altogether.

Psychedelic-inspired approaches for treating neurodegenerative disorders

Psychedelics are increasingly being recognized for their potential to treat a wide range of brain disorders including depression, post-traumatic stress disorder (PTSD), and substance use disorder. Their broad therapeutic potential might result from an ability to rescue cortical atrophy common to many neuropsychiatric and neurodegenerative diseases by impacting neurotrophic factor gene expression, activating neuronal growth and survival mechanisms, and modulating the immune system. While the therapeutic potential of psychedelics has not yet been extended to neurodegenerative disorders, we provide evidence suggesting that approaches based on psychedelic science might prove useful for treating these diseases. The primary target of psychedelics, the 5-HT_2A receptor, plays key roles in cortical neuron health and is dysregulated in Alzheimer's disease. Moreover, evidence suggests that psychedelics and related compounds could prove useful for treating the behavioral and psychological symptoms of dementia (BPSD). While more research is needed to probe the effects of psychedelics in models of neurodegenerative diseases, the robust effects of these compounds on structural and functional neuroplasticity and inflammation clearly warrant further investigation.

Ayahuasca for the Treatment of Depression

Ayahuasca, the vine of the souls in Quechua, is a psychedelic brew with a few formulations that most often include the bark of a liana in the Malpighiaceae family (Banisteriopsis caapi), with leaves from a shrub in the coffee family Rubiaceae (Psychotria viridis). Mixed with water and boiled for hours or days, it produces a brownish-colored liquid with a strong and characteristic taste. Ayahuasca contains the psychedelic tryptamine N,N-Dimethyltryptamine (DMT), and Monoamine Oxidase Inhibitors (MAOi), and in the past few years, it has been tested. In recent years its antidepressant properties have been put to the test. Evidence from open and randomized placebo-controlled clinical trials has shown encouraging results, indicating significant and rapid antidepressant effects, starting as early as 1 day after the ayahuasca intervention. In addition, we have explored the nature of these effects using multivariate measures. In this article, we will review the history, pharmacology, clinical trials, and clinical and behavioral markers associated with the antidepressant effects of ayahuasca.

Psychedelics as Novel Therapeutics in Alzheimer's Disease: Rationale and Potential Mechanisms

Serotonin 2A receptor (5-HT_2AR) agonist "classic psychedelics" are drawing increasing interest as potential mental health treatments. Recent work suggests psychedelics can exert persisting anxiolytic and antidepressant effects lasting up to several months after a single administration. Data indicate acute subjective drug effects as important psychological factors involved in observed therapeutic benefits. Additionally, animal models have shown an important role for 5-HT_2AR agonists in modulating learning and memory function with relevance for Alzheimer's Disease (AD) and related dementias. A number of biological mechanisms of action are under investigation to elucidate 5-HT_2AR agonists' therapeutic potential, including enhanced neuroplasticity, anti-inflammatory effects, and alterations in brain functional connectivity. These diverse lines of research are reviewed here along with a discussion of AD pathophysiology and neuropsychiatric symptoms to highlight classic psychedelics as potential novel pharmacotherapies for patients with AD. Human clinical research suggests a possible role for high-dose psychedelic administration in symptomatic treatment of depressed mood and anxiety in early-stage AD. Preclinical data indicate a potential for low- or high-dose psychedelic treatment regimens to slow or reverse brain atrophy, enhance cognitive function, and slow progression of AD. In conclusion, rationale and potential approaches for preliminary research with psychedelics in patients with AD are presented, and ramifications of this line of investigation for development of novel AD treatments are discussed.

Prolonged epigenomic and synaptic plasticity alterations following single exposure to a psychedelic in mice

Clinical evidence suggests that rapid and sustained antidepressant action can be attained with a single exposure to psychedelics. However, the biological substrates and key mediators of psychedelics' enduring action remain unknown. Here, we show that a single administration of the psychedelic DOI produces fast-acting effects on frontal cortex dendritic spine structure and acceleration of fear extinction via the 5-HT2A receptor. Additionally, a single dose of DOI leads to changes in chromatin organization, particularly at enhancer regions of genes involved in synaptic assembly that stretch for days after the psychedelic exposure. These DOI-induced alterations in the neuronal epigenome overlap with genetic loci associated with schizophrenia, depression, and attention deficit hyperactivity disorder. Together, these data support that epigenomic-driven changes in synaptic plasticity sustain psychedelics' long-lasting antidepressant action but also warn about potential substrate overlap with genetic risks for certain psychiatric conditions.

Psychedelics and Other Psychoplastogens for Treating Mental Illness

Psychedelics have inspired new hope for treating brain disorders, as they seem to be unlike any treatments currently available. Not only do they produce sustained therapeutic effects following a single administration, they also appear to have broad therapeutic potential, demonstrating efficacy for treating depression, post-traumatic stress disorder (PTSD), anxiety disorders, substance abuse disorder, and alcohol use disorder, among others. Psychedelics belong to a more general class of compounds known as psychoplastogens, which robustly promote structural and functional neural plasticity in key circuits relevant to brain health. Here we discuss the importance of structural plasticity in the treatment of neuropsychiatric diseases, as well as the evidence demonstrating that psychedelics are among the most effective chemical modulators of neural plasticity studied to date. Furthermore, we provide a theoretical framework with the potential to explain why psychedelic compounds produce long-lasting therapeutic effects across a wide range of brain disorders. Despite their promise as broadly efficacious neurotherapeutics, there are several issues associated with psychedelic-based medicines that drastically limit their clinical scalability. We discuss these challenges and how they might be overcome through the development of non-hallucinogenic psychoplastogens. The clinical use of psychedelics and other psychoplastogenic compounds marks a paradigm shift in neuropsychiatry toward therapeutic approaches relying on the selective modulation of neural circuits with small molecule drugs. Psychoplastogen research brings us one step closer to actually curing mental illness by rectifying the underlying pathophysiology of disorders like depression, moving beyond simply treating disease symptoms. However, determining how to most effectively deploy psychoplastogenic medicines at scale will be an important consideration as the field moves forward.

Rediscovering Psilocybin as an Antidepressive Treatment Strategy

There has recently been a renewal of interest in psychedelic research on the use of psilocybin in psychiatric treatment and, in particular, for the treatment of major depressive disorder (MDD). Several state-of-the-art studies have provided new insight into the mechanisms of action of psilocybin and its therapeutic potential. Nevertheless, many questions remain unanswered. With this review, we provide an overview of the current state of research on the potential mechanisms of psilocybin, its antidepressant potential, and the associated risks and adverse effects, to provide an update on a controversial topic discussed in psychopharmacology. A database search was conducted in Medline including articles on psilocybin over the period of the last 20 years. Despite the promising progress in understanding the mechanisms of psilocybin, the exact antidepressive mechanism and the role of the psychedelic experience remain elusive. The studies included in this review found high treatment effect sizes for psilocybin as an antidepressant. However, the results must be regarded as preliminary due to several limitations. Although the current studies observed no severe adverse events, several questions regarding safety and utility remain and must be subject of future research.

Engineering Safer Psychedelics for Treating Addiction

Addiction is best described as a disorder of maladaptive neuroplasticity involving the simultaneous strengthening of reward circuitry that drives compulsive drug seeking and weakening of circuits involved in executive control over harmful behaviors. Psychedelics have shown great promise for treating addiction, with many people attributing their therapeutic effects to insights gained while under the influence of the drug. However, psychedelics are also potent psychoplastogens—molecules capable of rapidly re-wiring the adult brain. The advent of non-hallucinogenic psychoplastogens with anti-addictive properties raises the intriguing possibility that hallucinations might not be necessary for all therapeutic effects of psychedelic-based medicines, so long as the underlying pathological neural circuitry can be remedied. One of these non-hallucinogenic psychoplastogens, tabernanthalog (TBG), appears to have long-lasting therapeutic effects in preclinical models relevant to alcohol and opioid addiction. Here, we discuss the implications of these results for the development of addiction treatments, as well as the next steps for advancing TBG and related non-hallucinogenic psychoplastogens as addiction therapeutics.

Psilocybin induces rapid and persistent growth of dendritic spines in frontal cortex in vivo

Psilocybin is a serotonergic psychedelic with untapped therapeutic potential. There are hints that the use of psychedelics can produce neural adaptations, although the extent and timescale of the impact in a mammalian brain are unknown. In this study, we used chronic two-photon microscopy to image longitudinally the apical dendritic spines of layer 5 pyramidal neurons in the mouse medial frontal cortex. We found that a single dose of psilocybin led to ∼10% increases in spine size and density, driven by an elevated spine formation rate. The structural remodeling occurred quickly within 24 h and was persistent 1 month later. Psilocybin also ameliorated stress-related behavioral deficit and elevated excitatory neurotransmission. Overall, the results demonstrate that psilocybin-evoked synaptic rewiring in the cortex is fast and enduring, potentially providing a structural trace for long-term integration of experiences and lasting beneficial actions.

Psychedelic-inspired drug discovery using an engineered biosensor

Ligands can induce G protein-coupled receptors (GPCRs) to adopt a myriad of conformations, many of which play critical roles in determining the activation of specific signaling cascades associated with distinct functional and behavioral consequences. For example, the 5-hydroxytryptamine 2A receptor (5-HT2AR) is the target of classic hallucinogens, atypical antipsychotics, and psychoplastogens. However, currently available methods are inadequate for directly assessing 5-HT2AR conformation both in vitro and in vivo. Here, we developed psychLight, a genetically encoded fluorescent sensor based on the 5-HT2AR structure. PsychLight detects behaviorally relevant serotonin release and correctly predicts the hallucinogenic behavioral effects of structurally similar 5-HT2AR ligands. We further used psychLight to identify a non-hallucinogenic psychedelic analog, which produced rapid-onset and long-lasting antidepressant-like effects after a single administration. The advent of psychLight will enable in vivo detection of serotonin dynamics, early identification of designer drugs of abuse, and the development of 5-HT2AR-dependent non-hallucinogenic therapeutics.

The Potential Role of Psychedelic Drugs in Mental Health Care of the Future

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide (LSD), or dimethyltryptamine (DMT), as well as psychoactive drugs that trigger phenomenologically- related experiences like 3,4-methylenedioxymethamphetamine (MDMA) and ketamine, belong to the most promising treatment approaches in contemporary psychiatry. Psychedelic-assisted psychotherapy is not only a new treatment paradigm in psychopharmacology, but it also requires a redefinition of psychotherapeutic processes and the contextualization of psychopharmacological interventions within a new treatment infrastructure. Crucial for future practice and research in the field are (1) informed patient referral and co-treatment practices, (2) screening (e. g., choosing the right patients for these therapies), (3) the dosing preparation sessions, (4) the assisted dosing sessions as well as after-care procedures such as (5) psychological integration and (6) supporting the development of structured patient communities. Definition of future treatment delivery infrastructures and requirements for therapist training are further challenges for research and practice. Finally, the implementation of psychedelic-assisted psychotherapy in routine mental health care must be embedded into public communication about the potential and risks of these innovative therapeutic approaches. This paper provides a synopsis of challenges for practitioners, researchers, and regulators to be addressed in the approval processes of psychedelics.

The Subjective Effects of Psychedelics Are Necessary for Their Enduring Therapeutic Effects

Classic psychedelics produce altered states of consciousness that individuals often interpret as meaningful experiences. Across a number of human studies, when the participant-rated intensity of the overall drug effects are statistically controlled for, certain subjective effects predict therapeutic and other desirable outcomes. Underlying neurobiological mechanisms are likely necessary but not sufficient to confer full and enduring beneficial effects. We propose that the subjective effects of psychedelics are necessary for their enduring beneficial effects and that these subjective effects account for the majority of their benefit.

Predicting Reactions to Psychedelic Drugs: A Systematic Review of States and Traits Related to Acute Drug Effects

Psychedelic drugs are increasingly being incorporated into therapeutic contexts for the purposes of promoting mental health. However, they can also induce adverse reactions in some individuals, and it is difficult to predict before treatment who is likely to experience positive or adverse acute effects. Although consideration of setting and dosage as well as excluding individuals with psychotic predispositions has thus far led to a high degree of safety, it is imperative that researchers develop a more nuanced understanding of how to predict individual reactions. To this end, the current systematic review coalesced the results of 14 studies that included baseline states or traits predictive of the acute effects of psychedelics. Individuals high in the traits of absorption, openness, and acceptance as well as a state of surrender were more likely to have positive and mystical-type experiences, whereas those low in openness and surrender or in preoccupied, apprehensive, or confused psychological states were more likely to experience acute adverse reactions. Participant sex was not a robust predictor of drug effects, but 5-HT2AR binding potential, executive network node diversity, and rACC volume may be potential baseline biomarkers related to acute reactions. Finally, increased age and experience with psychedelics were individual differences related to generally less intense effects, indicating that users may become slightly less sensitive to the effects of the drugs after repeated usage. Although future well-powered, placebo-controlled trials directly comparing the relative importance of these predictors is needed, this review synthesizes the field's current understanding of how to predict acute reactions to psychedelic drugs.

An analog of psychedelics restores functional neural circuits disrupted by unpredictable stress

Psychological stress affects a wide spectrum of brain functions and poses risks for many mental disorders. However, effective therapeutics to alleviate or revert its deleterious effects are lacking. A recently synthesized psychedelic analog tabernanthalog (TBG) has demonstrated anti-addictive and antidepressant potential. Whether TBG can rescue stress-induced affective, sensory, and cognitive deficits, and how it may achieve such effects by modulating neural circuits, remain unknown. Here we show that in mice exposed to unpredictable mild stress (UMS), administration of a single dose of TBG decreases their anxiety level and rescues deficits in sensory processing as well as in cognitive flexibility. Post-stress TBG treatment promotes the regrowth of excitatory neuron dendritic spines lost during UMS, decreases the baseline neuronal activity, and enhances whisking-modulation of neuronal activity in the somatosensory cortex. Moreover, calcium imaging in head-fixed mice performing a whisker-dependent texture discrimination task shows that novel textures elicit responses from a greater proportion of neurons in the somatosensory cortex than do familiar textures. Such differential response is diminished by UMS and is restored by TBG. Together, our study reveals the effects of UMS on cortical neuronal circuit activity patterns and demonstrate that TBG combats the detrimental effects of stress by modulating basal and stimulus-dependent neural activity in cortical networks.

Critical Period Plasticity as a Framework for Psychedelic-Assisted Psychotherapy

As psychedelic compounds gain traction in psychiatry, there is a need to consider the active mechanism to explain the effect observed in randomized clinical trials. Traditionally, biological psychiatry has asked how compounds affect the causal pathways of illness to reduce symptoms and therefore focus on analysis of the pharmacologic properties. In psychedelic-assisted psychotherapy (PAP), there is debate about whether ingestion of the psychedelic alone is thought to be responsible for the clinical outcome. A question arises how the medication and psychotherapeutic intervention together might lead to neurobiological changes that underlie recovery from illness such as post-traumatic stress disorder (PTSD). This paper offers a framework for investigating the neurobiological basis of PAP by extrapolating from models used to explain how a pharmacologic intervention might create an optimal brain state during which environmental input has enduring effects. Specifically, there are developmental "critical" periods (CP) with exquisite sensitivity to environmental input; the biological characteristics are largely unknown. We discuss a hypothesis that psychedelics may remove the brakes on adult neuroplasticity, inducing a state similar to that of neurodevelopment. In the visual system, progress has been made both in identifying the biological conditions which distinguishes the CP and in manipulating the active ingredients with the idea that we might pharmacologically reopen a critical period in adulthood. We highlight ocular dominance plasticity (ODP) in the visual system as a model for characterizing CP in limbic systems relevant to psychiatry. A CP framework may help to integrate the neuroscientific inquiry with the influence of the environment both in development and in PAP.

Does Psychedelic Therapy Have a Transdiagnostic Action and Prophylactic Potential?

Addressing global mental health is a major 21st-century challenge. Current treatments have recognized limitations; in this context, new ones that are prophylactic and effective across diagnostic boundaries would represent a major advance. The view that there exists a core of transdiagnostic overlap between psychiatric disorders has re-emerged in recent years, and evidence that psychedelic therapy holds promise for a range of psychiatric disorders supports the position that it may be transdiagnostically effective. Here, we propose that psychedelic therapy's core, transdiagnostically relevant action lies in its ability to increase neuronal and mental plasticity, thus enhancing the potential for change, which we consider to be a key to its therapeutic benefits. Moreover, we suggest that enhanced plasticity via psychedelics, combined with a psychotherapeutic approach, can aid healthy adaptability and resilience, which are protective factors for long-term well-being. We present candidate neurological and psychological markers of this plasticity and link them with a predictive processing model of the action of psychedelics. We propose that a model of psychedelic-induced plasticity combined with an adequate therapeutic context has prophylactic and transdiagnostic potential, implying that it could have a broad, positive impact on public health.