The mixed serotonin receptor agonist psilocybin reduces threat-induced modulation of amygdala connectivity

Potential Differences in Psychedelic Actions Based on Biological Sex

The resurgence of interest in psychedelics as treatments for psychiatric disorders necessitates a better understanding of potential sex differences in response to these substances. Sex as a biological variable (SABV) has been historically neglected in medical research, posing limits to our understanding of treatment efficacy. Human studies have provided insights into the efficacy of psychedelics across various diagnoses and aspects of cognition, yet sex-specific effects remain unclear, making it difficult to draw strong conclusions about sex-dependent differences in response to psychedelic treatments. Compounding this further, animal studies used to understand biological mechanisms of psychedelics predominantly use one sex and present mixed neurobiological and behavioral outcomes. Studies that do include both sexes often do not investigate sex differences further, which may hinder the translation of findings to the clinic. In reviewing sex differences in responses to psychedelics, we will highlight the direct interaction between estrogen (the most extensively studied steroid hormone) and the serotonin system (central to the mechanism of action of psychedelics), and the potential that estrogen-serotonin interactions may influence the efficacy of psychedelics in female participants. Estrogen influences serotonin neurotransmission by affecting its synthesis and release, as well as modulating the sensitivity and responsiveness of serotonin receptor subtypes in the brain. This could potentially influence the efficacy of psychedelics in females by modifying their therapeutic efficacy across menstrual cycles and developmental stages. Investigating this interaction in the context of psychedelic research could aid in the advancement of therapeutic outcomes, especially for conditions with sex-specific prevalence.

Neural Mechanisms of Resting-State Networks and the Amygdala Underlying the Cognitive and Emotional Effects of Psilocybin

BACKGROUND

Serotonergic psychedelics, such as psilocybin, alter perceptual and cognitive systems that are functionally integrated with the amygdala. These changes can alter cognition and emotions that are hypothesized to contribute to their therapeutic utility. However, the neural mechanisms of cognitive and subcortical systems altered by psychedelics are not well understood.

METHODS

We used resting-state functional magnetic resonance images collected during a randomized, double-blind, placebo-controlled clinical trial of 24 healthy adults under 0.2 mg/kg psilocybin to estimate the directed (i.e., effective) changes between the amygdala and 3 large-scale resting-state networks involved in cognition. These networks are the default mode network, the salience network, and the central executive network.

RESULTS

We found a pattern of decreased top-down effective connectivity from these resting-state networks to the amygdala. Effective connectivity decreased within the default mode network and salience network but increased within the central executive network. These changes in effective connectivity were statistically associated with behavioral measures of altered cognition and emotion under the influence of psilocybin.

CONCLUSIONS

Our findings suggest that temporary amygdala signal attenuation is associated with mechanistic changes to resting-state network connectivity. These changes are significant for altered cognition and perception and suggest targets for research investigating the efficacy of psychedelic therapy for internalizing psychiatric disorders. More broadly, our study suggests the value of quantifying the brain's hierarchical organization using effective connectivity to identify important mechanisms for basic cognitive function and how they are integrated to give rise to subjective experiences.

Post-traumatic stress disorder: the role of the amygdala and potential therapeutic interventions - a review

Introduction

Post-traumatic stress disorder (PTSD) is a psychiatric disorder triggered by exposure to a life-threatening or sexually violent traumatic event, and is characterized by symptoms involving intrusive re-experiencing, persistent avoidance of associated stimuli, emotional and cognitive disturbances, and hyperarousal for long periods after the trauma has occurred. These debilitating symptoms induce occupational and social impairments that contribute to a significant clinical burden for PTSD patients, and substantial socioeconomic costs, reaching approximately $20,000 dollars per individual with PTSD each year in the US. Despite increased translational research focus in the field of PTSD, the development of novel, effective pharmacotherapies for its treatment remains an important unmet clinical need.

Observations

In this review, we summarize the evidence implicating dysfunctional activity of the amygdala in the pathophysiology of PTSD. We identify the transient receptor potential canonical (TRPC) ion channels as promising drug targets given their distribution in the amygdala, and evidence from animal studies demonstrating their role in fear response modulation. We discuss the evidence-based pharmacotherapy and psychotherapy treatment approaches for PTSD.

Discussion

In view of the prevalence and economic burden associated with PTSD, further investigation is warranted into novel treatment approaches based on our knowledge of the involvement of brain circuitry and the role of the amygdala in PTSD, as well as the potential added value of combined pharmacotherapy and psychotherapy to better manage PTSD symptoms.

[Psilocybin-Assisted Treatment of Depression, Anxiety and Substance use Disorders: Neurobiological Basis and Clinical Application]

Successful therapy of mental disorders is very important in view of the high level of suffering of those affected. Since established pharmaceutical and psychotherapeutic approaches do not lead to the desired improvement in all cases, complementary or alternative treatment methods are intensively researched. Psilocybin-assisted psychotherapy seems particularly promising, and has been approved in the USA for larger clinical trials. Psilocybin belongs to the group of psychedelics and influences psychological experiences. In assisted therapy, psilocybin is administered in controlled doses under medical supervision to patients with different mental disorders. In the studies conducted so far, longer-term positive effects could be shown after just one or a few doses. In order to provide a better understanding of the potential therapeutic mechanisms, this article will first describe neurobiological and psychological effects of psilocybin. To better assess the potential of psilocybin-assisted psychotherapy for various disorders, clinical studies conducted so far with patients administered psilocybin are reviewed.

Perioperative considerations for patients exposed to hallucinogens

Hallucinogen exposure in patients in the perioperative period presents challenges for anesthesiologists and other anesthesia providers. Acute and chronic exposure to these substances can cause physiological impacts that can affect the function of anesthetic and analgesic medications used during perioperative care. The objective of this narrative review is to educate readers on the wide array of hallucinogens and psychedelics that may influence the perioperative management of patients exposed to these substances. A narrative review of the literature surrounding hallucinogens and psychedelics was completed. Hallucinogens and psychedelics are quite varied in their mechanisms of action and therefore present a variety of perioperative implications and perioperative considerations. Many of these substances increase serotonin levels or act directly at serotonergic receptors. However, there are other relevant actions that may include varied mechanisms from N-methyl-D-aspartate receptor antagonism to stimulation of muscarinic receptors. With hallucinogen exposure rates on the rise, understanding the effects of hallucinogens is important for optimizing management and reducing risks perioperatively for patients with acute or chronic exposure.

Multimodal Neuroimaging of the Effect of Serotonergic Psychedelics on the Brain

The neurobiological mechanisms underpinning psychiatric disorders such as treatment-resistant major depression, post-traumatic stress disorder, and substance use disorders, remain unknown. Psychedelic compounds, such as psilocybin, lysergic acid diethylamide, and N,N-dimethyltryptamine, have emerged as potential therapies for these disorders because of their hypothesized ability to induce neuroplastic effects and alter functional networks in the brain. Yet, the mechanisms underpinning the neurobiological treatment response remain obscure. Quantitative neuroimaging is uniquely positioned to provide insight into the neurobiological mechanisms of these emerging therapies and quantify the patient treatment response. This review aims to synthesize our current state-of-the-art understanding of the functional changes occurring in the brain following psilocybin, lysergic acid diethylamide, or N,N-dimethyltryptamine administration in human participants with fMRI and PET. We further aim to disseminate our understanding of psychedelic compounds as they relate to neuroimaging with the goal of improved diagnostics and treatment of neuropsychiatric illness.

Multivariate patterns of brain functional connectome associated with COVID-19-related negative affect symptoms

Severe mental health problems with the representation of negative affect symptoms (NAS) have been increasingly reported during the coronavirus disease 2019 (COVID-19) pandemic. This study aimed to explore the multivariate patterns of brain functional connectome predicting COVID-19-related NAS. This cohort study encompassed a group of university students to undergo neuroimaging scans before the pandemic, and we re-contacted participants for 1-year follow-up COVID-related NAS evaluations during the pandemic. Regularized canonical correlation analysis was used to identify connectome-based dimensions of NAS to compute pairs of canonical variates. The predictive ability of identified functional connectome to NAS dimensional scores was examined with a nested cross-validation. Two dimensions (i.e. mode stress and mode anxiety) were related to distinct patterns of brain functional connectome (r2 = 0.911, PFDR = 0.048; r2 = 0.901, PFDR = 0.037, respectively). Mode anxiety was characterized by high loadings in connectivity between affective network (AFN) and visual network (VN), while connectivity of the default mode network with dorsal attention network (DAN) were remarkably prominent in mode stress. Connectivity patterns within the DAN and between DAN and VN, ventral attention network, and AFN was common for both dimensions. The identified functional connectome can reliably predict mode stress (r = 0.37, MAE = 5.1, p < 0.001) and mode anxiety (r = 0.28, MAE = 5.4, p = 0.005) in the cross-validation. Our findings provide new insight into multivariate dimensions of COVID-related NAS, which may have implications for developing network-based biomarkers in psychological interventions for vulnerable individuals in the pandemic.

The Psychedelic Future of Post-Traumatic Stress Disorder Treatment

Post-traumatic stress disorder (PTSD) is a mental health condition that can occur following exposure to a traumatic experience. An estimated 12 million U.S. adults are presently affected by this disorder. Current treatments include psychological therapies (e.g., exposure-based interventions) and pharmacological treatments (e.g., selective serotonin reuptake inhibitors (SSRIs)). However, a significant proportion of patients receiving standard-of-care therapies for PTSD remain symptomatic, and new approaches for this and other trauma-related mental health conditions are greatly needed. Psychedelic compounds that alter cognition, perception, and mood are currently being examined for their efficacy in treating PTSD despite their current status as Drug Enforcement Administration (DEA)- scheduled substances. Initial clinical trials have demonstrated the potential value of psychedelicassisted therapy to treat PTSD and other psychiatric disorders. In this comprehensive review, we summarize the state of the science of PTSD clinical care, including current treatments and their shortcomings. We review clinical studies of psychedelic interventions to treat PTSD, trauma-related disorders, and common comorbidities. The classic psychedelics psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT) and DMT-containing ayahuasca, as well as the entactogen 3,4-methylenedioxymethamphetamine (MDMA) and the dissociative anesthetic ketamine, are reviewed. For each drug, we present the history of use, psychological and somatic effects, pharmacology, and safety profile. The rationale and proposed mechanisms for use in treating PTSD and traumarelated disorders are discussed. This review concludes with an in-depth consideration of future directions for the psychiatric applications of psychedelics to maximize therapeutic benefit and minimize risk in individuals and communities impacted by trauma-related conditions.

Potential use of psilocybin drugs in the treatment of depression

INTRODUCTION

Depression is a common disabling psychiatric disorder, which - in extreme cases - may lead to suicide if untreated or inadequately treated. Despite the availability of various treatments for depression, including pharmacotherapy, there is still a need to search for new agents with higher effectiveness and faster onset of action, especially for patients with treatment-resistant depression.

AREAS COVERED

A substance that has attracted considerable attention for nearly a decade is psilocybin, a natural psychedelic found in psilocybin mushrooms. In this study, we evaluated the efficacy and safety of psilocybin in the treatment of depression, based on pivotal randomized clinical trials. Moreover, we used findings from observational studies regarding recreational use. We also looked at ongoing clinical trials and discussed the registration status and clinical potential of the drug.

EXPERT OPINION

Clinical phase I-II trials published to date reported promising results for psilocybin in the treatment of patients with major depressive disorder and treatment-resistant depression, in a relatively short time after administration. However, before psilocybin is approved for use and administered to patients with depression, the results of large ongoing phase III clinical trials are needed to confirm its efficacy and safety and to change the way it is perceived by physicians and patients.

Psychedelic therapy in the treatment of addiction: the past, present and future

Psychedelic therapy has witnessed a resurgence in interest in the last decade from the scientific and medical communities with evidence now building for its safety and efficacy in treating a range of psychiatric disorders including addiction. In this review we will chart the research investigating the role of these interventions in individuals with addiction beginning with an overview of the current socioeconomic impact of addiction, treatment options, and outcomes. We will start by examining historical studies from the first psychedelic research era of the mid-late 1900s, followed by an overview of the available real-world evidence gathered from naturalistic, observational, and survey-based studies. We will then cover modern-day clinical trials of psychedelic therapies in addiction from first-in-human to phase II clinical trials. Finally, we will provide an overview of the different translational human neuropsychopharmacology techniques, including functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), that can be applied to foster a mechanistic understanding of therapeutic mechanisms. A more granular understanding of the treatment effects of psychedelics will facilitate the optimisation of the psychedelic therapy drug development landscape, and ultimately improve patient outcomes.

Sex-specific effects of psychedelic drug exposure on central amygdala reactivity and behavioral responding

Psilocybin and its active metabolite psilocin have been shown to elicit rapid and long-lasting symptom improvements in a variety of affective psychiatric illnesses. However, the region-specific alterations underlying these therapeutic effects remain relatively unknown. The central amygdala (CeA) is a primary output region within the extended amygdala that is dysregulated in affective psychiatric disorders. Here, we measured CeA activity using the activity marker c-Fos and CeA reactivity using fiber photometry paired with an aversive air-puff stimulus. We found that psilocin administration acutely increased CeA activity in both males and females and increased stimulus specific CeA reactivity in females, but not males. In contrast, psilocin produced time-dependent decreases in reactivity in males, but not in females, as early as 2 days and lasting to 28 days post administration. We also measured behavioral responses to the air-puff stimulus and found sex-dependent changes in threat responding but not exploratory behavior or general locomotion. Repeated presentations of the auditory component of the air-puff were also performed and sex-specific effects of psilocin on CeA reactivity to the auditory-alone stimulus were also observed. This study provides new evidence that a single dose of psilocin produces sex-specific, time-dependent, and enduring changes in CeA reactivity and behavioral responding to specific components of an aversive stimulus.

Low doses of lysergic acid diethylamide (LSD) increase reward-related brain activity

Renewed interest in classic psychedelics as treatments for psychiatric disorders warrants a deeper understanding of their neural mechanisms. Single, high doses of psychedelic drugs have shown promise in treating depressive disorders, perhaps by reversing deficits in reward processing in the brain. In addition, there are anecdotal reports that repeated ingestion of low doses of LSD, or "microdosing", improve mood, cognition, and feelings of wellbeing. However, the effects of low doses of classic psychedelics on reward processing have not been studied. The current study examined the effects of two single, low doses of LSD compared to placebo on measures of reward processing. Eighteen healthy adults completed three sessions in which they received placebo (LSD-0), 13 μg LSD (LSD-13) and 26 μg LSD (LSD-26) in a within-subject, double-blind design. Neural activity was recorded while participants completed the electrophysiological monetary incentive delay task. Event-related potentials were measured during feedback processing (Reward-Positivity: RewP, Feedback-P3: FB-P3, and Late-Positive Potential: LPP). Compared to placebo, LSD-13 increased RewP and LPP amplitudes for reward (vs. neutral) feedback, and LSD-13 and LSD-26 increased FB-P3 amplitudes for positive (vs. negative) feedback. These effects were unassociated with most subjective measures of drug effects. Thus, single, low doses of LSD (vs. placebo) increased three reward-related ERP components reflecting increased hedonic (RewP), motivational (FB-P3), and affective processing of feedback (LPP). These results constitute the first evidence that low doses of LSD increase reward-related brain activity in humans. These findings may have important implications for the treatment of depressive disorders.

Mini-review: The neurobiology of treating substance use disorders with classical psychedelics

The potential of psychedelics to persistently treat substance use disorders is known since the 1960s. However, the biological mechanisms responsible for their therapeutic effects have not yet been fully elucidated. While it is known that serotonergic hallucinogens induce changes in gene expression and neuroplasticity, particularly in prefrontal regions, theories on how specifically this counteracts the alterations that occur in neuronal circuitry throughout the course of addiction are largely unknown. This narrative mini-review endeavors to synthesize well-established knowledge from addiction research with findings and theories regarding the neurobiological effects of psychedelics to give an overview of the potential mechanisms that underlie the treatment of substance use disorders with classical hallucinogenic compounds and point out gaps in the current understanding.

Psychedelic-Induced Serotonin 2A Receptor Downregulation Does Not Predict Swim Stress Coping in Mice

Serotoninergic psychedelics such as psilocybin have been reported to elicit a long-lasting reduction in depressive symptoms. Although the main target for serotoninergic psychedelics, serotonin type 2A receptor (5-HT_2A), has been established, the possible mechanism of the antidepressant action of psychedelics remains unknown. Using the mouse forced swim test model, we examined whether the administration of the synthetic serotoninergic psychedelic 2,5-dimethoxy-4-iodoamphetamine (DOI) would modulate 5-HT_2A receptor levels in the medial prefrontal cortex (mPFC) and revert stress-induced changes in behavior. Mice subjected to swim stress developed a passive stress-coping strategy when tested in the forced swim test 6 days later. This change in behavior was not associated with the hypothesized increase in 5-HT_2A receptor-dependent head twitch behaviors or consistent changes in 5-HT_2A receptor levels in the mPFC. When DOI was administered 1 day before the forced swim test, a low dose (0.2 mg/kg i.p.) unexpectedly increased immobility while a high dose (2 mg/kg i.p.) had no significant effect on immobility. Nevertheless, DOI evoked a dose-dependent decrease in 5-HT_2A levels in the mPFC of mice previously exposed to swim stress. Our findings do not support the hypothesis that the downregulation of 5-HT_2A receptors in the mPFC contributes to the antidepressant-like properties of serotoninergic psychedelics.

Neural Mechanisms and Psychology of Psychedelic Ego Dissolution

Neuroimaging studies of psychedelics have advanced our understanding of hierarchical brain organization and the mechanisms underlying their subjective and therapeutic effects. The primary mechanism of action of classic psychedelics is binding to serotonergic 5-HT2A receptors. Agonist activity at these receptors leads to neuromodulatory changes in synaptic efficacy that can have a profound effect on hierarchical message-passing in the brain. Here, we review the cognitive and neuroimaging evidence for the effects of psychedelics: in particular, their influence on selfhood and subject-object boundaries-known as ego dissolution-surmised to underwrite their subjective and therapeutic effects. Agonism of 5-HT2A receptors, located at the apex of the cortical hierarchy, may have a particularly powerful effect on sentience and consciousness. These effects can endure well after the pharmacological half-life, suggesting that psychedelics may have effects on neural plasticity that may play a role in their therapeutic efficacy. Psychologically, this may be accompanied by a disarming of ego resistance that increases the repertoire of perceptual hypotheses and affords alternate pathways for thought and behavior, including those that undergird selfhood. We consider the interaction between serotonergic neuromodulation and sentience through the lens of hierarchical predictive coding, which speaks to the value of psychedelics in understanding how we make sense of the world and specific predictions about effective connectivity in cortical hierarchies that can be tested using functional neuroimaging. SIGNIFICANCE STATEMENT: Classic psychedelics bind to serotonergic 5-HT2A receptors. Their agonist activity at these receptors leads to neuromodulatory changes in synaptic efficacy, resulting in a profound effect on information processing in the brain. Here, we synthesize an abundance of brain imaging research with pharmacological and psychological interpretations informed by the framework of predictive coding. Moreover, predictive coding is suggested to offer more sophisticated interpretations of neuroimaging findings by bridging the role between the 5-HT2A receptors and large-scale brain networks.

A Research Domain Criteria (RDoC)-Guided Dashboard to Review Psilocybin Target Domains: A Systematic Review

BACKGROUND

Preliminary results from randomized controlled studies as well as identified molecular, cellular, and circuit targets of select psychedelics (e.g., psilocybin) suggest that their effects are transdiagnostic. In this review, we exploit the Research Domain Criteria (RDoC) transdiagnostic framework, to synthesize extant literature on psilocybin.

OBJECTIVE

We aimed to identify RDoC-based effects of psilocybin and vistas for future mechanistic and interventional research.

METHODS

A systematic search in electronic databases (i.e., PubMed, Scopus, PsycINFO, and Web of Science) performed in January and February 2021 identified English articles published between 1990 and 2020 reporting the effects of psilocybin on mental health measures. Data from included articles were retrieved and organized according to the RDoC bio-behavioral matrix and its constituent six main domains, namely: positive valence systems, negative valence systems, cognitive systems, social processes, sensorimotor systems, and arousal and regulatory systems.

RESULTS

The preponderance of research with psilocybin has differentially reported beneficial effects on positive valence systems, negative valence system, and social process domains. The data from the included studies support both short-term (23 assessments) and long-term (15 assessments) beneficial effects of psilocybin on the positive valence systems. While 12 of the extracted outcome measures suggest that psilocybin use is associated with increases in the "fear" construct of the negative valence systems domain, 19 findings show no significant effects on this construct, and seven parameters show lowered levels of the "sustained threat" construct in the long term. Thirty-four outcome measures revealed short-term alterations in the social systems' construct namely, "perception and understanding of self," and "social communications" as well as enhancements in "perception and understanding of others" and "affiliation and attachment". The majority of findings related to the cognitive systems' domain reported dyscognitive effects. There have been relatively few studies reporting outcomes of psilocybin on the remaining RDoC domains. Moreover, seven of the included studies suggest the transdiagnostic effects of psilocybin. The dashboard characterization of RDoC outcomes with psilocybin suggests beneficial effects in the measures of reward, threat, and arousal, as well as general social systems.

CONCLUSIONS

Psilocybin possesses a multi-domain effectiveness. The field would benefit from highly rigorous proof-of-mechanism research to assess the effects of psilocybin using the RDoC framework. The combined effect of psilocybin with psychosocial interventions with RDoC-based outcomes is a priority therapeutic vista.

Psychedelics in the treatment of unipolar and bipolar depression

This is a narrative review about the role of classic and two atypical psychedelics in the treatment of unipolar and bipolar depression. Since the 1990s, psychedelics experience a renaissance in biomedical research. The so-called classic psychedelics include lysergic acid diethylamide (LSD), psilocybin, mescaline and ayahuasca. Characteristic effects like alterations in sensory perception, as well as emotion- and self-processing are induced by stimulation of serotonin 2A receptors in cortical areas. The new paradigm of psychedelic-assisted psychotherapy suggests a therapeutic framework in which a safely conducted psychedelic experience is integrated into a continuous psychotherapeutic process. First randomized, controlled trials with psilocybin show promising efficacy, tolerability, and adherence in the treatment of unipolar depression. On the other hand, classic psychedelics seem to be associated with the induction of mania, which is an important issue to consider for the design of research and clinical protocols. So called atypical psychedelics are a heterogeneous group with overlapping subjective effects but different neurobiological mechanisms. Two examples of therapeutic value in psychiatry are 3,4-methyl​enedioxy​methamphetamine (MDMA) and ketamine. Since 2020 the ketamine enantiomer esketamine has been granted international approval for treatment-resistant unipolar depression, and also first evidence exists for the therapeutic efficacy of ketamine in bipolar depression. Whether psychedelics will fulfil current expectations and find their way into broader clinical use will depend on future rigorous clinical trials with larger sample sizes. A well-considered therapeutic and legal framework will be crucial for these substances to create new treatment settings and a potential paradigm shift.

The Effects of Psilocybin in Adults with Major Depressive Disorder and the General Population: Findings from Neuroimaging Studies

The use of psilocybin as treatment for major depressive disorder (MDD) has been examined as a promising alternative to traditional first-line options. We reviewed existing literature to provide a synthesis of the extant neuroimaging observations with psilocybin, and to identify putative therapeutic targets for target engagement studies with psilocybin, and potentially other psychedelics. We assessed neuroimaging observations with psilocybin among participants with MDD and healthy populations. A systematic search was conducted on PubMed, Google Scholar and PsycINFO from database inception to November 17th, 2021. The study quality (i.e., risk of bias) was assessed using the revised Cochrane risk-of-bias tool for randomized trials. A total of ten studies evaluated psilocybin in healthy populations and three studies assessed psilocybin in MDD participants using neuroimaging techniques. Following psilocybin administration, a decrease in amygdala activity and a reduction in depressive symptoms was observed in two studies. Changes in functional connectivity and activation of prefrontal limbic structures, specifically the ventral medial prefrontal cortex and amygdala, was seen in healthy populations. There was high heterogeneity in methodology (e.g., dosing schedule and imaging methods) amongst included studies. Longitudinal studies are needed to further elucidate psilocybin treatment for MDD, its long-term effects and the possibility of sustained therapeutic effects.

Effects of a psychedelic 5-HT2A receptor agonist on anxiety-related behavior and fear processing in mice

Psychedelic-assisted psychotherapy gained considerable interest as a novel treatment strategy for fear-related mental disorders but the underlying mechanism remains poorly understood. The serotonin 2A (5-HT2A) receptor is a key target underlying the effects of psychedelics on emotional arousal but its role in fear processing remains controversial. Using the psychedelic 5-HT2A/5-HT2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) and 5-HT2A receptor knockout (KO) mice we investigated the effect of 5-HT2A receptor activation on emotional processing. We show that DOI administration did not impair performance in a spontaneous alternation task but reduced anxiety-like avoidance behavior in the elevated plus maze and elevated zero maze tasks. Moreover, we found that DOI did not block memory recall but diminished fear expression in a passive avoidance task. Likewise, DOI administration reduced fear expression in an auditory fear conditioning paradigm, while it did not affect retention of fear extinction when administered prior to extinction learning. The effect of DOI on fear expression was abolished in 5-HT2A receptor KO mice. Administration of DOI induced a significant increase of c-Fos expression in specific amygdalar nuclei. Moreover, local infusion of the 5-HT2A receptor antagonist M100907 into the amygdala reversed the effect of systemic administration of DOI on fear expression while local administration of DOI into the amygdala was sufficient to suppress fear expression. Our data demonstrate that activation of 5-HT2A receptors in the amygdala suppresses fear expression but provide no evidence for an effect on retention of fear extinction.

Psychoactive Drugs in the Management of Post Traumatic Stress Disorder: A Promising New Horizon

Post-traumatic stress disorder (PTSD) is an anxiety disorder that often presents after exposure to a traumatic, life-threatening event. Experiencing a traumatic event is not rare, with inciting incidents ranging from being burglarized to politically motivated genocide. While traditional psychopharmacology and psychotherapy are the mainstays of the treatment of PTSD currently, psychoactive drugs (otherwise known as psychedelics) are being explored for their novel role in the treatment of PTSD patients. Psychoactive drugs such as MDMA, ketamine, and psilocybin have been shown to specifically target and decrease fear and anxiety pathways in the brain. These unique properties hold the potential to be utilized in addressing symptoms of trauma in those with refractory or treatment-resistant PTSD. Historically, federal and state laws have restricted research into how psychoactive drugs can be used to treat mental illness due to the widespread belief that these drugs present more harm than benefit. However, the current shift in public opinion on psychedelics has propelled research to look into the benefits of these drugs for patients with mental illness. This article aims to discuss the mechanisms of how MDMA, ketamine, and psilocybin work in the PTSD brain, as well as their beneficial role in treatment.

A neurobiological perspective on social influence: Serotonin and social adaptation

Humans are inherently social beings. Being suggestible to each other's expectations enables pro-social skills that are crucial for social learning and adaptation. Despite its high relevance for psychiatry, the neurobiological mechanisms underlying social adaptation are still not well understood. This review therefore provides a conceptual framework covering various distinct mechanisms underlying social adaptation and explores the neuropharmacology - in particular the role of the serotonin (5-HT) system - modulating these mechanisms. This article therefore reviews empirical results on social influence processing and reconciles them with recent findings from psychedelic research on social processing to elucidate neurobiological and neuropharmacological underpinnings of social adaptation. Various computational, neurobiological, and neurochemical processes are involved in distinct mechanisms underlying social adaptation such as the multisensory process of social information integration that is crucial for the forming of self-representation and representations of social norms. This is again associated with self- and other-perception during social interactions as well as value-based decision making that guides our behaviour in daily interactions. We highlight the critical role of 5-HT in these processes and suggest that 5-HT can facilitate social learning and may represent an important target for treating psychiatric disorders characterized by impairments in social functioning. This framework also has important implications for psychedelic-assisted therapy as well as for the development of novel treatment approaches and future research directions.

Prospective examination of the therapeutic role of psychological flexibility and cognitive reappraisal in the ceremonial use of ayahuasca

BACKGROUND

Evidence suggests that psychedelic-assisted therapy carries transdiagnostic efficacy in the treatment of mental health conditions characterized by low mood and the use of avoidance coping strategies.

AIMS

While preliminary evidence suggests that psychological flexibility and emotion regulation processes play an important role within psychedelic therapy, this prospective study addressed methodological gaps in the literature and examined the ability of ayahuasca to stimulate acute states of cognitive reappraisal and long-term changes in psychological flexibility and mood. The study also explored whether moderating factors predisposed participants to experience therapeutic changes.

METHODS

Participants (N = 261) were recruited from three Shipibo ayahuasca retreat centers in Central and South America and completed assessments on mood, psychological flexibility, and acute ceremonial factors. Expectancy, demand characteristics, and invalid responding were controlled for with several validity scales.

RESULTS/OUTCOMES

Participants reported significant reductions in negative mood after three months, as well as increases in positive mood and psychological flexibility. Acute experiences of reappraisal during the ayahuasca ceremony exerted the strongest moderating effects on increases in positive mood and psychological flexibility. Increases in psychological flexibility statistically mediated the effects of acute psychological factors, including reappraisal, on changes in positive mood.

CONCLUSIONS/INTERPRETATION

These results highlight the role of acute psychological processes, such as reappraisal, and post-acute increases in psychological flexibility as putative mechanisms underlying positive outcomes associated with psychedelics. These results also provide support for the integration of third-wave and mindfulness-based therapy approaches with psychedelic-assisted interventions.

Classic Psychedelic Drugs: Update on Biological Mechanisms

Renewed interest in the effects of psychedelics in the treatment of psychiatric disorders warrants a better understanding of the neurobiological mechanisms underlying the effects of these substances. During the past two decades, state-of-the-art studies of animals and humans have yielded new important insights into the molecular, cellular, and systems-level actions of psychedelic drugs. These efforts have revealed that psychedelics affect primarily serotonergic receptor subtypes located in cortico-thalamic and cortico-cortical feedback circuits of information processing. Psychedelic drugs modulate excitatory-inhibitory balance in these circuits and can participate in neuroplasticity within brain structures critical for the integration of information relevant to sensation, cognition, emotions, and the narrative of self. Neuroimaging studies showed that characteristic dimensions of the psychedelic experience obtained through subjective questionnaires as well as alterations in self-referential processing and emotion regulation obtained through neuropsychological tasks are associated with distinct changes in brain activity and connectivity patterns at multiple-system levels. These recent results suggest that changes in self-experience, emotional processing, and social cognition may contribute to the potential therapeutic effects of psychedelics.

Dynamic Causal Modeling of the Prefrontal/Amygdala Network During Processing of Emotional Faces

Introduction: The importance of the amygdala/medial orbitofrontal cortex (OFC) network during processing of emotional stimuli, emotional faces in particular, is well established. This premise is supported by converging evidence from animal models, human neuroanatomical results, and neuroimaging studies. However, there is missing evidence from human brain connectivity studies that the OFC and no other prefrontal brain areas such as the dorsolateral prefrontal cortex (DLPFC) or ventrolateral prefrontal cortex (VLPFC) are responsible for amygdala regulation in the functional context of emotional face stimuli. Methods: Dynamic causal modeling of ultrahigh-field functional magnetic resonance imaging data acquired at 7 Tesla in 38 healthy subjects and a well-established paradigm for emotional face processing were used to assess the central role of the OFC to provide empirical validation for the assumed network architecture. Results: Using Bayesian model selection, it is demonstrated that indeed the OFC, and not the VLPFC and the DLPFC, downregulates amygdala activation during the emotion discrimination task. In addition, Bayesian model averaging group results were rigorously tested using bootstrapping, further corroborating these findings and providing an estimator for robustness and optimal sample sizes. Discussion: While it is true that VLPFC and DLPFC are relevant for the processing of emotional faces and are connected to the OFC, the OFC appears to be a central hub for the prefrontal/amygdala interaction.

Psychedelics and hallucinogens in Psychiatry: finding new pharmacological targets

BACKGROUND

The therapeutic options for neurobehavioral disorders are still limited, and in many cases, they lack a satisfactory balance between efficacy and side effects.

OBJECTIVE

This work aims to review current evidence regarding the potential contribution of psychedelics and hallucinogens to the discovery of new drugs for treating different psychiatric disorders.

DISCUSSION

Ayahuasca/N,N-dimethyltryptamine (DMT), lysergic acid diethylamide (LSD), and psilocybin have evidence supporting their use in depression, and psilocybin and ayahuasca have also shown good results in treatment-resistant depression. In randomized controlled trials (RCTs) conducted with anxious patients, there were symptomatic improvements with psilocybin and LSD. Psilocybin diminished Yale-Brown Obsessive Compulsive Scale (Y-BOCS) scores in a small obsessive-compulsive disorder (OCD) sample. The evidence is less robust regarding substance use disorders, but it suggests a possible role for LSD and psilocybin in alcohol use disorders and for psilocybin in tobacco addiction. In a clinical setting, these substances seem to be safe and well-tolerated. Their mechanisms of action are not fully elucidated, but there seems to be a preponderant role of 5-hydroxytryptamine (5HT) 2A agonism, as well as connectivity changes within the default mode network (DMN) and amygdala and some other molecular modifications.

CONCLUSION

The studies underlying the conclusions have small samples and are heterogeneous in their methods. However, the results suggest that the use of psychedelics and hallucinogens could be considered in some disorders. More studies are needed to reinforce their evidence as potential new drugs.

Dynamic Causal Modeling on the Identification of Interacting Networks in the Brain: A Systematic Review

Dynamic causal modeling (DCM) has long been used to characterize effective connectivity within networks of distributed neuronal responses. Previous reviews have highlighted the understanding of the conceptual basis behind DCM and its variants from different aspects. However, no detailed summary or classification research on the task-related effective connectivity of various brain regions has been made formally available so far, and there is also a lack of application analysis of DCM for hemodynamic and electrophysiological measurements. This review aims to analyze the effective connectivity of different brain regions using DCM for different measurement data. We found that, in general, most studies focused on the networks between different cortical regions, and the research on the networks between other deep subcortical nuclei or between them and the cerebral cortex are receiving increasing attention, but far from the same scale. Our analysis also reveals a clear bias towards some task types. Based on these results, we identify and discuss several promising research directions that may help the community to attain a clear understanding of the brain network interactions under different tasks.

Psychedelics, Sociality, and Human Evolution

Our hominin ancestors inevitably encountered and likely ingested psychedelic mushrooms throughout their evolutionary history. This assertion is supported by current understanding of: early hominins' paleodiet and paleoecology; primate phylogeny of mycophagical and self-medicative behaviors; and the biogeography of psilocybin-containing fungi. These lines of evidence indicate mushrooms (including bioactive species) have been a relevant resource since the Pliocene, when hominins intensified exploitation of forest floor foods. Psilocybin and similar psychedelics that primarily target the serotonin 2A receptor subtype stimulate an active coping strategy response that may provide an enhanced capacity for adaptive changes through a flexible and associative mode of cognition. Such psychedelics also alter emotional processing, self-regulation, and social behavior, often having enduring effects on individual and group well-being and sociality. A homeostatic and drug instrumentalization perspective suggests that incidental inclusion of psychedelics in the diet of hominins, and their eventual addition to rituals and institutions of early humans could have conferred selective advantages. Hominin evolution occurred in an ever-changing, and at times quickly changing, environmental landscape and entailed advancement into a socio-cognitive niche, i.e., the development of a socially interdependent lifeway based on reasoning, cooperative communication, and social learning. In this context, psychedelics' effects in enhancing sociality, imagination, eloquence, and suggestibility may have increased adaptability and fitness. We present interdisciplinary evidence for a model of psychedelic instrumentalization focused on four interrelated instrumentalization goals: management of psychological distress and treatment of health problems; enhanced social interaction and interpersonal relations; facilitation of collective ritual and religious activities; and enhanced group decision-making. The socio-cognitive niche was simultaneously a selection pressure and an adaptive response, and was partially constructed by hominins through their activities and their choices. Therefore, the evolutionary scenario put forward suggests that integration of psilocybin into ancient diet, communal practice, and proto-religious activity may have enhanced hominin response to the socio-cognitive niche, while also aiding in its creation. In particular, the interpersonal and prosocial effects of psilocybin may have mediated the expansion of social bonding mechanisms such as laughter, music, storytelling, and religion, imposing a systematic bias on the selective environment that favored selection for prosociality in our lineage.

The Effects of Tryptamine Psychedelics in the Brain: A meta-Analysis of Functional and Review of Molecular Imaging Studies

There is an increasing interest in the neural effects of psychoactive drugs, in particular tryptamine psychedelics, which has been incremented by the proposal that they have potential therapeutic benefits, based on their molecular mimicry of serotonin. It is widely believed that they act mainly through 5HT2A receptors but their effects on neural activation of distinct brain systems are not fully understood. We performed a quantitative meta-analysis of brain imaging studies to investigate the effects of substances within this class (e.g., LSD, Psilocybin, DMT, Ayahuasca) in the brain from a molecular and functional point of view. We investigated the question whether the changes in activation patterns and connectivity map into regions with larger 5HT1A/5HT2A receptor binding, as expected from indolaemine hallucinogens (in spite of the often reported emphasis only on 5HT2AR). We did indeed find that regions with changed connectivity and/or activation patterns match regions with high density of 5HT2A receptors, namely visual BA19, visual fusiform regions in BA37, dorsal anterior and posterior cingulate cortex, medial prefrontal cortex, and regions involved in theory of mind such as the surpramarginal gyrus, and temporal cortex (rich in 5HT1A receptors). However, we also found relevant patterns in other brain regions such as dorsolateral prefrontal cortex. Moreover, many of the above-mentioned regions also have a significant density of both 5HT1A/5HT2A receptors, and available PET studies on the effects of psychedelics on receptor occupancy are still quite scarce, precluding a metanalytic approach. Finally, we found a robust neuromodulatory effect in the right amygdala. In sum, the available evidence points towards strong neuromodulatory effects of tryptamine psychedelics in key brain regions involved in mental imagery, theory of mind and affective regulation, pointing to potential therapeutic applications of this class of substances.

The Therapeutic Potential of Psilocybin

The psychedelic effects of some plants and fungi have been known and deliberately exploited by humans for thousands of years. Fungi, particularly mushrooms, are the principal source of naturally occurring psychedelics. The mushroom extract, psilocybin has historically been used as a psychedelic agent for religious and spiritual ceremonies, as well as a therapeutic option for neuropsychiatric conditions. Psychedelic use was largely associated with the "hippie" counterculture movement, which, in turn, resulted in a growing, and still lingering, negative stigmatization for psychedelics. As a result, in 1970, the U.S. government rescheduled psychedelics as Schedule 1 drugs, ultimately ending scientific research on psychedelics. This prohibition on psychedelic drug research significantly delayed advances in medical knowledge on the therapeutic uses of agents such as psilocybin. A 2004 pilot study from the University of California, Los Angeles, exploring the potential of psilocybin treatment in patients with advanced-stage cancer managed to reignite interest and significantly renewed efforts in psilocybin research, heralding a new age in exploration for psychedelic therapy. Since then, significant advances have been made in characterizing the chemical properties of psilocybin as well as its therapeutic uses. This review will explore the potential of psilocybin in the treatment of neuropsychiatry-related conditions, examining recent advances as well as current research. This is not a systematic review.

Psilocybin and MDMA for the treatment of trauma-related psychopathology

This review examines the role of trauma in psychiatric morbidity and analogous psychoneurobiological changes. Trauma is a necessary criterion for Post-Traumatic Stress Disorder (PTSD), however, trauma history is highly correlated with a variety of psychiatric conditions. Some evidence suggests that Major Depressive Disorder (MDD) is the most common psychiatric condition that arises following trauma. Approximately 50% of PTSD cases present with co-morbid MDD. Overlapping symptomatology and neurobiology between these conditions underlie the debate over whether these phenomena result from problematic nosology or whether comorbid MDD + PTSD is a distinct phenotype of trauma-related psychopathology. Regardless, similar treatment approaches have been employed historically, with varying success. The drug-assisted psychotherapy treatment model, which combines pharmacological and psychotherapeutic approaches, is currently being trialled as a novel treatment approach in psychiatry. Both psilocybin- and 3,4-Methylenedioxymethamphetamine (MDMA)-assisted psychotherapy have received Food and Drug Administration 'breakthrough therapy' designation for the treatment of resistant MDD and PTSD, respectively. This paper reviews the therapeutic rationale of both psilocybin and MDMA for treating both trauma-related MDD and PTSD.

Clinical and biological predictors of psychedelic response in the treatment of psychiatric and addictive disorders: A systematic review

BACKGROUND

The use of psychedelic treatments has shown very promising results in some psychiatric and addictive disorders, but not all patients achieved a response.

AIM

The aim of this review is to explore the clinical and biological factors which could predict the response to psychedelics in psychiatric and addictive disorders.

METHODS

A systematic research was performed on MEDLINE, PsycInfo, Web of science, and Scopus databases from January 1990 to May 2020. All studies investigating the predictive factors of response to psychedelics regardless of psychiatric or addictive disorders, were included.

RESULTS

Twenty studies investigating addictive disorder, treatment-resistant depression, obsessive-compulsive disorder and depressive and anxiety symptoms in patients with life-threatening cancer were included in this review. We found that, in all indications, the main predictive factor of response to psychedelics is the intensity of the acute psychedelic experience. Indeed, we found this factor for alcohol and tobacco use disorders, treatment-resistant depression, and anxiety and depressive symptoms in patients with life-threatening cancer, but not for obsessive-compulsive disorder.

CONCLUSION

The intensity of the acute psychedelic experience was the main predicting factor of response. The action mechanism of this experience was not clear, but some hypotheses could be made, such as a modulation of serotoninergic system by 5-HT2A receptors agonism, a modulation of the default mode network (DMN) with an acute modular disintegration of the DMN followed by a re-integration of this network with a normal functioning, or an anti-inflammatory effect of this treatment.

Naturalistic Use of Mescaline Is Associated with Self-Reported Psychiatric Improvements and Enduring Positive Life Changes

Mescaline is a naturally occurring psychoactive alkaloid that has been used as a sacrament by Indigenous populations in spiritual ritual and healing ceremonies for millennia. Despite promising early preliminary research and favorable anecdotal reports, there is limited research investigating mescaline's psychotherapeutic potential. We administered an anonymous online questionnaire to adults (N = 452) reporting use of mescaline in naturalistic settings about mental health benefits attributed to mescaline. We assessed respondents' self-reported improvements in depression, anxiety, post-traumatic stress disorder (PTSD), and alcohol and drug use disorders (AUD and DUD). Of the respondents reporting histories of these clinical conditions, most (68-86%) reported subjective improvement following their most memorable mescaline experience. Respondents who reported an improvement in their psychiatric conditions reported significantly higher ratings of acute psychological factors including mystical-type, psychological insight, and ego dissolution effects compared to those who did not report improvements (Cohen's d range 0.7 - 1.5). Many respondents (35-50%) rated the mescaline experience as the single or top five most spiritually significant or meaningful experience(s) of their lives. Acute experiences of psychological insight during their mescaline experience were associated with increased odds of reporting improvement in depression, anxiety, AUD and DUD. Additional research is needed to corroborate these preliminary findings and to rigorously examine the efficacy of mescaline for psychiatric treatment in controlled, longitudinal clinical trials.

Classical Psychedelics as Therapeutics in Psychiatry - Current Clinical Evidence and Potential Therapeutic Mechanisms in Substance Use and Mood Disorders

Classical psychedelics, primarily psilocybin and lysergic acid diethylamide (LSD), have been used and extensively studied in Western medicine as part of substance-assisted psychotherapy in the 1950s and 1960s. Modern clinical research is currently gaining momentum and provides new evidence for the safety and efficacy of classical psychedelics (primarily psilocybin, but also LSD and ayahuasca) in the treatment of different psychiatric conditions, including substance use and mood disorders.In this review article, we outline common pathological mechanisms of substance use disorders (SUD) and unipolar depression. Next, the current literature on the effects of psychedelics is summarized in order to generate hypotheses regarding their potential therapeutic mechanisms of action in treating these psychiatric conditions. Finally, we review and discuss clinical trials published since 2011 investigating the effects of psychedelics in SUD and depression.While results from those modern clinical trials are promising, most of them do not meet the methodological requirements to allow firm conclusions on the clinical efficacy of psychedelics. Larger, blinded, randomized controlled trials (RCT) with clearly defined patient groups and well-defined primary endpoints are needed. Additionally, the therapeutic mechanisms of classical psychedelics are currently unknown. This review presents hypotheses derived from preclinical and human studies that need to be tested in future trials to better understand the clinical potential of psychedelic substances in modern psychiatry.

Psychedelic drugs: neurobiology and potential for treatment of psychiatric disorders

Renewed interest in the use of psychedelics in the treatment of psychiatric disorders warrants a better understanding of the neurobiological mechanisms underlying the effects of these substances. After a hiatus of about 50 years, state-of-the art studies have recently begun to close important knowledge gaps by elucidating the mechanisms of action of psychedelics with regard to their effects on receptor subsystems, systems-level brain activity and connectivity, and cognitive and emotional processing. In addition, functional studies have shown that changes in self-experience, emotional processing and social cognition may contribute to the potential therapeutic effects of psychedelics. These discoveries provide a scientific road map for the investigation and application of psychedelic substances in psychiatry.

Psilocybin acutely alters the functional connectivity of the claustrum with brain networks that support perception, memory, and attention

Psychedelic drugs, including the serotonin 2a (5-HT2A) receptor partial agonist psilocybin, are receiving renewed attention for their possible efficacy in treating a variety of neuropsychiatric disorders. Psilocybin induces widespread dysregulation of cortical activity, but circuit-level mechanisms underlying this effect are unclear. The claustrum is a subcortical nucleus that highly expresses 5-HT2A receptors and provides glutamatergic inputs to arguably all areas of the cerebral cortex. We therefore tested the hypothesis that psilocybin modulates claustrum function in humans. Fifteen healthy participants (10M, 5F) completed this within-subjects study in which whole-brain resting-state blood-oxygenation level-dependent (BOLD) signal was measured 100 ​min after blinded oral administration of placebo and 10 mg/70 ​kg psilocybin. Left and right claustrum signal was isolated using small region confound correction. Psilocybin significantly decreased both the amplitude of low frequency fluctuations as well as the variance of BOLD signal in the left and right claustrum. Psilocybin also significantly decreased functional connectivity of the right claustrum with auditory and default mode networks (DMN), increased right claustrum connectivity with the fronto-parietal task control network (FPTC), and decreased left claustrum connectivity with the FPTC. DMN integrity was associated with right-claustrum connectivity with the DMN, while FPTC integrity and modularity were associated with right claustrum and left claustrum connectivity with the FPTC, respectively. Subjective effects of psilocybin predicted changes in the amplitude of low frequency fluctuations and the variance of BOLD signal in the left and right claustrum. Observed effects were specific to claustrum, compared to flanking regions of interest (the left and right insula and putamen). This study used a pharmacological intervention to provide the first empirical evidence in any species for a significant role of 5-HT2A receptor signaling in claustrum functioning, and supports a possible role of the claustrum in the subjective and therapeutic effects of psilocybin.

A potential role for psilocybin in the treatment of obsessive-compulsive disorder

The recent revivification of interest in the therapeutic use of psychedelics has had a particular focus on mood disorders and addiction, although there is reason to think these drugs may be effective more widely. After outlining pertinent aspects of psilocybin and obsessive-compulsive disorder (OCD), the current review summarizes the evidence indicating that there may be a role for psilocybin in the treatment of OCD, as well as highlighting a range of potential therapeutic mechanisms that reflect the action of psilocybin on brain function. Although the current evidence is limited, that multiple signals point in directions consistent with treatment potential, alongside the psychological and physiological safety of clinically administered psilocybin, support the expansion of research, both in animal models and in further randomized controlled trials, to properly investigate this potential.

Preliminary Report on the Effects of a Low Dose of LSD on Resting-State Amygdala Functional Connectivity

BACKGROUND

The practice of "microdosing," or the use of repeated, very low doses of lysergic acid diethylamide (LSD) to improve mood or cognition, has received considerable public attention, but empirical studies are lacking. Controlled studies are needed to investigate both the therapeutic potential and the neurobiological underpinnings of this pharmacologic treatment.

METHODS

The present study was designed to examine the effects of a single low dose of LSD (13 μg) versus placebo on resting-state functional connectivity and cerebral blood flow in healthy young adults. Twenty men and women, 18 to 35 years old, participated in 2 functional magnetic resonance imaging scanning sessions in which they received placebo or LSD under double-blind conditions. During each session, the participants completed drug effect and mood questionnaires, and physiological measures were recorded. During expected peak drug effect, they underwent resting-state blood oxygen level-dependent and arterial spin labeling scans. Cerebral blood flow as well as amygdala and thalamic connectivity were analyzed.

RESULTS

LSD increased amygdala seed-based connectivity with the right angular gyrus, right middle frontal gyrus, and the cerebellum, and decreased amygdala connectivity with the left and right postcentral gyrus and the superior temporal gyrus. This low dose of LSD had weak and variable effects on mood, but its effects on positive mood were positively correlated with the increase in amygdala-middle frontal gyrus connectivity strength.

CONCLUSIONS

These preliminary findings show that a very low dose of LSD, which produces negligible subjective changes, alters brain connectivity in limbic circuits. Additional studies, especially with repeated dosing, will reveal whether these neural changes are related to the drug's purported antidepressant effect.

Rostral Anterior Cingulate Thickness Predicts the Emotional Psilocybin Experience

Psilocybin is the psychoactive compound of mushrooms in the psilocybe species. Psilocybin directly affects a number of serotonin receptors, with highest affinity for the serotonin 2A receptor (5HT-2Ar). Generally, the effects of psilocybin, and its active metabolite psilocin, are well established and include a range of cognitive, emotional, and perceptual perturbations. Despite the generality of these effects, there is a high degree of inter-individual variability in subjective psilocybin experiences that are not well understood. Others have shown brain morphology metrics derived from magnetic resonance imaging (MRI) can predict individual drug response. Due to high expression of serotonin 2A receptors (5HT-2Ar) in the cingulate cortex, and its prior associations with psilocybin, we investigate if cortical thickness of this structure predicts the psilocybin experience in healthy adults. We hypothesized that greater cingulate thickness would predict higher subjective ratings in sub-scales of the Five-Dimensional Altered State of Consciousness (5D-ASC) with high emotionality in healthy participants (n = 55) who received oral psilocybin (either low dose: 0.160 mg/kg or high dose: 0.215 mg/kg). After controlling for sex, age, and using false discovery rate (FDR) correction, we found the rostral anterior cingulate predicted all four emotional sub-scales, whereas the caudal and posterior cingulate did not. How classic psychedelic compounds induce such large inter-individual variability in subjective states has been a long-standing question in serotonergic research. These results extend the traditional set and setting hypothesis of the psychedelic experience to include brain structure metrics.

Emotions and brain function are altered up to one month after a single high dose of psilocybin

Psilocybin is a classic psychedelic compound that may have efficacy for the treatment of mood and substance use disorders. Acute psilocybin effects include reduced negative mood, increased positive mood, and reduced amygdala response to negative affective stimuli. However, no study has investigated the long-term, enduring impact of psilocybin on negative affect and associated brain function. Twelve healthy volunteers (7F/5M) completed an open-label pilot study including assessments 1-day before, 1-week after, and 1-month after receiving a 25 mg/70 kg dose of psilocybin to test the hypothesis that psilocybin administration leads to enduring changes in affect and neural correlates of affect. One-week post-psilocybin, negative affect and amygdala response to facial affect stimuli were reduced, whereas positive affect and dorsal lateral prefrontal and medial orbitofrontal cortex responses to emotionally-conflicting stimuli were increased. One-month post-psilocybin, negative affective and amygdala response to facial affect stimuli returned to baseline levels while positive affect remained elevated, and trait anxiety was reduced. Finally, the number of significant resting-state functional connections across the brain increased from baseline to 1-week and 1-month post-psilocybin. These preliminary findings suggest that psilocybin may increase emotional and brain plasticity, and the reported findings support the hypothesis that negative affect may be a therapeutic target for psilocybin.

Increased amygdala-visual cortex connectivity in youth with persecutory ideation

BACKGROUND

Subclinical delusional ideas, including persecutory beliefs, in otherwise healthy individuals are heritable symptoms associated with increased risk for psychotic illness, possibly representing an expression of one end of a continuum of psychosis severity. The identification of variation in brain function associated with these symptoms may provide insights about the neurobiology of delusions in clinical psychosis.

METHODS

A resting-state functional magnetic resonance imaging scan was collected from 131 young adults with a wide range of severity of subclinical delusional beliefs, including persecutory ideas. Because of evidence for a key role of the amygdala in fear and paranoia, resting-state functional connectivity of the amygdala was measured.

RESULTS

Connectivity between the amygdala and early visual cortical areas, including striate cortex (V1), was found to be significantly greater in participants with high (n = 43) v. low (n = 44) numbers of delusional beliefs, particularly in those who showed persistence of those beliefs. Similarly, across the full sample, the number of and distress associated with delusional beliefs were positively correlated with the strength of amygdala-visual cortex connectivity. Moreover, further analyses revealed that these effects were driven by those who endorsed persecutory beliefs.

CONCLUSIONS

These findings are consistent with the hypothesis that aberrant assignments of threat to sensory stimuli may lead to the downstream development of delusional ideas. Taken together with prior findings of disrupted sensory-limbic coupling in psychosis, these results suggest that altered amygdala-visual cortex connectivity could represent a marker of psychosis-related pathophysiology across a continuum of symptom severity.

Classical psychedelics for the treatment of depression and anxiety: A systematic review

BACKGROUND

Depression and anxiety are prevalent psychiatric disorders that carry significant morbidity. Pharmacological and psychosocial interventions are used to manage these conditions, but their efficacy is limited. Recent interest into the use of psychedelic-assisted therapy using ayahuasca, psilocybin or lysergic acid diethylamide (LSD) may be a promising alternative for patients unresponsive to traditional treatments. This review aims to determine the efficacy and tolerability of psychedelics in the management of resistant depression.

METHODS

Clinical trials investigating psychedelics in patients with depression and/or anxiety were searched via MEDLINE, EMBASE and PsychINFO. Efficacy was assessed by measuring symptom improvement from baseline, and tolerability was evaluated by noting the incidence and type of adverse effects reported. Risk of bias was assessed.

RESULTS

Seven studies, with 130 patients, were analysed in this review. Three were conducted in patients with depression, two in patients with anxiety and two in patients with both. In a supportive setting, ayahuasca, psilocybin, and LSD consistently produced immediate and significant anti-depressant and anxiolytic effects that were endured for several months. Psychedelics were well-tolerated. The most common adverse effects were transient anxiety, short-lived headaches, nausea and mild increases in heart rate and blood pressure.

LIMITATIONS

At present, the number of studies on this subject is very limited; and the number of participating patients within these is also limited as the treatment under investigations is a relatively novel concept.

CONCLUSIONS

Though further evidence is required, psychedelics appear to be effective in significantly reducing symptoms of depression and anxiety and are well-tolerated.

Cessation and reduction in alcohol consumption and misuse after psychedelic use

BACKGROUND

Meta-analysis of randomized studies using lysergic acid diethylamide (LSD) for alcohol use disorder (AUD) showed large, significant effects for LSD efficacy compared to control conditions. Clinical studies suggest potential anti-addiction effects of LSD and mechanistically-related classic psychedelics for alcohol and other substance use disorders.

AIMS

To supplement clinical studies, reports of psychedelic use in naturalistic settings can provide further data regarding potential effects of psychedelics on alcohol use.

METHODS

An anonymous online survey of individuals with prior AUD reporting cessation or reduction in alcohol use following psychedelic use in non-clinical settings.

RESULTS

343 respondents, mostly White (89%), males (78%), in the USA (60%) completed the survey. Participants reported seven years of problematic alcohol use on average before the psychedelic experience to which they attributed reduced alcohol consumption, with 72% meeting retrospective criteria for severe AUD. Most reported taking a moderate or high dose of LSD (38%) or psilocybin (36%), followed by significant reduction in alcohol consumption. After the psychedelic experience 83% no longer met AUD criteria. Participants rated their psychedelic experience as highly meaningful and insightful, with 28% endorsing psychedelic-associated changes in life priorities or values as facilitating reduced alcohol misuse. Greater psychedelic dose, insight, mystical-type effects, and personal meaning of experiences were associated with a greater reduction in alcohol consumption, controlling for prior alcohol consumption and related distress.

CONCLUSIONS

Although results cannot demonstrate causality, they suggest that naturalistic psychedelic use may lead to cessation or reduction in problematic alcohol use, supporting further investigation of psychedelic-assisted treatment for AUD.

Classic psychedelics: the special role of the visual system

Here, we briefly overview the various aspects of classic serotonergic hallucinogens reported by a number of studies. One of the key hypotheses of our paper is that the visual effects of psychedelics might play a key role in resetting fears. Namely, we especially focus on visual processes because they are among the most prominent features of hallucinogen-induced hallucinations. We hypothesize that our brain has an ancient visual-based (preverbal) intrinsic cognitive process that, during the transient inhibition of top-down convergent and abstract thinking (mediated by the prefrontal cortex) by psychedelics, can neutralize emotional fears of unconscious and conscious life experiences from the past. In these processes, the decreased functional integrity of the self-referencing processes of the default mode network, the modified multisensory integration (linked to bodily self-consciousness and self-awareness), and the modified amygdala activity may also play key roles. Moreover, the emotional reset (elimination of stress-related emotions) by psychedelics may induce psychological changes and overwrite the stress-related neuroepigenetic information of past unconscious and conscious emotional fears.

REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics

This paper formulates the action of psychedelics by integrating the free-energy principle and entropic brain hypothesis. We call this formulation relaxed beliefs under psychedelics (REBUS) and the anarchic brain, founded on the principle that-via their entropic effect on spontaneous cortical activity-psychedelics work to relax the precision of high-level priors or beliefs, thereby liberating bottom-up information flow, particularly via intrinsic sources such as the limbic system. We assemble evidence for this model and show how it can explain a broad range of phenomena associated with the psychedelic experience. With regard to their potential therapeutic use, we propose that psychedelics work to relax the precision weighting of pathologically overweighted priors underpinning various expressions of mental illness. We propose that this process entails an increased sensitization of high-level priors to bottom-up signaling (stemming from intrinsic sources), and that this heightened sensitivity enables the potential revision and deweighting of overweighted priors. We end by discussing further implications of the model, such as that psychedelics can bring about the revision of other heavily weighted high-level priors, not directly related to mental health, such as those underlying partisan and/or overly-confident political, religious, and/or philosophical perspectives. SIGNIFICANCE STATEMENT: Psychedelics are capturing interest, with efforts underway to bring psilocybin therapy to marketing authorisation and legal access within a decade, spearheaded by the findings of a series of phase 2 trials. In this climate, a compelling unified model of how psychedelics alter brain function to alter consciousness would have appeal. Towards this end, we have sought to integrate a leading model of global brain function, hierarchical predictive coding, with an often-cited model of the acute action of psychedelics, the entropic brain hypothesis. The resulting synthesis states that psychedelics work to relax high-level priors, sensitising them to liberated bottom-up information flow, which, with the right intention, care provision and context, can help guide and cultivate the revision of entrenched pathological priors.

Changes in global and thalamic brain connectivity in LSD-induced altered states of consciousness are attributable to the 5-HT2A receptor

Background:

Lysergic acid diethylamide (LSD) has agonist activity at various serotonin (5-HT) and dopamine receptors. Despite the therapeutic and scientific interest in LSD, specific receptor contributions to its neurobiological effects remain unknown.

Methods:

We therefore conducted a double-blind, randomized, counterbalanced, cross-over studyduring which 24 healthy human participants received either (i) placebo+placebo, (ii) placebo+LSD (100 µg po), or (iii) Ketanserin, a selective 5-HT2A receptor antagonist,+LSD. We quantified resting-state functional connectivity via a data-driven global brain connectivity method and compared it to cortical gene expression maps.

Results:

LSD reduced associative, but concurrently increased sensory-somatomotor brain-wide and thalamic connectivity. Ketanserin fully blocked the subjective and neural LSD effects. Whole-brain spatial patterns of LSD effects matched 5-HT2A receptor cortical gene expression in humans.

Conclusions:

Together, these results strongly implicate the 5-HT2A receptor in LSD’s neuropharmacology. This study therefore pinpoints the critical role of 5-HT2A in LSD’s mechanism, which informs its neurobiology and guides rational development of psychedelic-based therapeutics.

Funding:

Funded by the Swiss National Science Foundation, the Swiss Neuromatrix Foundation, the Usona Institute, the NIH, the NIAA, the NARSAD Independent Investigator Grant, the Yale CTSA grant, and the Slovenian Research Agency.

Clinical trial number:

NCT02451072.

The psychedelic drug LSD alters thinking and perception. Users can experience hallucinations, in which they, for example, see things that are not there. Colors, sounds and objects can appear distorted, and time can seem to speed up or slow down. These changes bear some resemblance to the changes in thinking and perception that occur in certain psychiatric disorders, such as schizophrenia. Studying how LSD affects the brain could thus offer insights into the mechanisms underlying these conditions. There is also evidence that LSD itself could help to reduce the symptoms of depression and anxiety disorders.

Preller et al. have now used brain imaging to explore the effects of LSD on the brains of healthy volunteers. This revealed that LSD reduced communication among brain areas involved in planning and decision-making, but it increased communication between areas involved in sensation and movement. Volunteers whose brains showed the most communication between sensory and movement areas also reported the strongest effects of LSD on their thinking and perception.

Preller et al. also found that another drug called Ketanserin prevented LSD from altering how different brain regions communicate. It also prevented LSD from inducing changes in thinking and perception. Ketanserin blocks a protein called the serotonin 2A receptor, which is activated by a brain chemical called serotonin that, amongst other roles, helps to regulate mood. By mapping the location of the gene that produces the serotonin 2A receptor, Preller et al. showed that the receptor is present in brain regions that show altered communication after LSD intake, therefore pinpointing the importance of this receptor in the effects of LSD.

Psychiatric disorders that produce psychotic symptoms affect vast numbers of people worldwide. Further research into how LSD affects the brain could help us to better understand how such symptoms arise, and may also lead to the development of more effective treatments for a range of mental health conditions.