Multisensory perceptual and causal inference is largely preserved in medicated post-acute individuals with schizophrenia.

Hallucinations and perceptual abnormalities in psychosis are thought to arise from imbalanced integration of prior information and sensory inputs. We combined psychophysics, Bayesian modeling, and electroencephalography (EEG) to investigate potential changes in perceptual and causal inference in response to audiovisual flash-beep sequences in medicated individuals with schizophrenia who exhibited limited psychotic symptoms. Seventeen participants with schizophrenia and 23 healthy controls reported either the number of flashes or the number of beeps of audiovisual sequences that varied in their audiovisual numeric disparity across trials. Both groups balanced sensory integration and segregation in line with Bayesian causal inference rather than resorting to simpler heuristics. Both also showed comparable weighting of prior information regarding the signals' causal structure, although the schizophrenia group slightly overweighted prior information about the number of flashes or beeps. At the neural level, both groups computed Bayesian causal inference through dynamic encoding of independent estimates of the flash and beep counts, followed by estimates that flexibly combine audiovisual inputs. Our results demonstrate that the core neurocomputational mechanisms for audiovisual perceptual and causal inference in number estimation tasks are largely preserved in our limited sample of medicated post-acute individuals with schizophrenia. Future research should explore whether these findings generalize to unmedicated patients with acute psychotic symptoms.

[Auditory hallucinations in a pregnant patient caused by autoimmune encephalitis]. / Auditieve hallucinaties bij een zwangere pa­-tiënte op basis van auto-immuunencefalitis.

In this case report we describe a pregnant woman with newly developed auditory hallucinations, initially seen by a psychiatrist of the psychiatric emergency service. The day after assessment , the patient developed epileptic seizures and was referred to the hospital. After additional blood and liquor tests and an MRI scan, an autoimmune encephalitis was diagnosed. She was treated with prednisolone and immunoglobulins. She made a full recovery and gave birth to a healthy son at term. In this article we describe the diagnostic considerations, the course and treatment, the importance of being alert to a somatic cause of psychiatric symptoms and of multidisciplinary collaboration.

Carbamazepine responsive episodic dystonia and hallucination due to pyruvate dehydrogenase E2 (DLAT) gene mutation.

Pyruvate Dehydrogenase (PDH) E2 deficiency due to Dihydrolipoamide acetyltransferase (DLAT) mutations is a very rare condition with only nine reported cases to date. We describe a 15-year-old girl with mild intellectual disability, paroxysmal dystonia and bilateral basal ganglia signal abnormalities on brain magnetic resonance imaging (MRI). Additionally, neurophysiological, imaging, metabolic and exome sequencing studies were performed. Routine metabolite testing, and GLUT1 and PRRT2 mutation analysis were negative. A repeat brain MRI revealed 'Eye-of-the-tiger-sign'. Exome sequencing identified homozygous valine to glycine alteration at amino acid position 157 in the DLAT gene. Bioinformatic and family analyses indicated that the alteration was likely pathogenic. Patient's dystonia was responsive to low-dose carbamazepine. On weaning carbamazepine, patient developed hallucinations which resolved after carbamazepine was restarted. PDH E2 deficiency due to DLAT mutation has a more benign course compared to common forms of PDH E1 deficiency due to X-linked PDHA1 mutations. All known cases of PDH E2 deficiency due to DLAT mutations share the features of episodic dystonia and intellectual disability. Our patient's dystonia and hallucinations responded well to low-dose carbamazepine.

Long-term follow-up of participants in ketamine clinical trials for mood disorders.

BACKGROUND: Participants who received ketamine at the NIMH were among the first to receive ketamine for depression in controlled clinical trials, providing a unique opportunity to assess long-term outcomes. This analysis evaluated the relationship between participating in a ketamine clinical trial and subsequent ketamine/esketamine use after leaving the research setting. METHODS: Participants seen within the NIMH Experimental Therapeutics and Pathophysiology Branch from 2002 to 2022 (n = 1000) were contacted for follow-up assessment. Participants reported whether they had used ketamine/esketamine, sought non-prescribed ketamine, attempted suicide, or been psychiatrically hospitalized since discharge. Information regarding their recent depressive symptoms, dissociative symptoms, and hallucinations was also collected. RESULTS: Of the 203 participants in follow-up assessments (55 % female, average time since leaving NIMH = 9.04 years), 52 (25.6 %) had originally received ketamine at the NIMH, and the rest had participated in non-ketamine studies. Individuals who had received ketamine at the NIMH were more likely to have received ketamine/esketamine post-discharge than those who did not receive ketamine at the NIMH (OR = 0.25, p < .001). Participants who reported using ketamine/esketamine post-discharge reported more depressive symptoms than those who had not (p < .001). Receiving ketamine at the NIMH was not associated with differences in suicide attempts, psychiatric hospitalizations, dissociation, hallucinations, or attempt to obtain non-prescribed ketamine. LIMITATIONS: Low follow-up study participation rate; varying time since discharge. CONCLUSIONS: Participants who received ketamine in an NIMH clinical trial were more likely to receive ketamine/esketamine post-discharge, but none reported symptoms indicating abuse. Results underscore the critical need for long-term follow-up of individuals receiving these and other rapid-acting antidepressants. CLINICAL TRIALS IDENTIFIER: NCT04877977.

On the Optimal Diagnosis and the Evolving Role of Pimavanserin in Parkinson's Disease Psychosis.

Parkinson's disease (PD) is associated with the development of psychosis (PDP), including hallucinations and delusions, in more than half of the patient population. Optimal PD management must therefore involve considerations about both motor and non-motor symptoms. Often, clinicians fail to diagnosis psychosis in patients with PD and, when it is recognized, treat it suboptimally, despite the availability of multiple interventions. In this paper, we provide a summary of the current guidelines and clinical evidence for treating PDP with antipsychotics. We also provide recommendations for diagnosis and follow-up. Finally, an updated treatment algorithm for PDP that incorporates the use of pimavanserin, the only US FDA-approved drug for the treatment of PDP, was developed by extrapolating from a limited evidence base to bridge to clinical practice using expert opinion and experience. Because pimavanserin is only approved for the treatment of PDP in the US, in other parts of the world other recommendations and algorithms must be considered.

Clearing the Fog: A Review of Antipsychotics for Parkinson's-Related Hallucinations: A Focus on Pimavanserin, Quetiapine and Clozapine.

Parkinson's disease is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms, including hallucinations. The use of antipsychotic medications is a common strategy to manage hallucinations associated with Parkinson's disease psychosis (PDP). However, careful consideration is necessary when selecting the most appropriate drug due to the potential risks associated with the available treatment options. Atypical antipsychotics (AAPs), such as Pimavanserin and Clozapine, have effectively controlled PDP symptoms. On the contrary, the support for utilizing quetiapine is not as substantial as other antipsychotics because research studies specifically investigating its application are still emerging and relatively recent. The broad mechanisms of action of AAPs, involving dopamine and serotonin receptors, provide improved outcomes and fewer side effects than typical antipsychotics. Conversely, other antipsychotics, including risperidone, olanzapine, aripiprazole, ziprasidone, and lurasidone, have been found to worsen motor symptoms and are generally not recommended for PDP. While AAPs offer favorable benefits, they are associated with specific adverse effects. Extrapyramidal symptoms, somnolence, hypotension, constipation, and cognitive impairment are commonly observed with AAP use. Clozapine, in particular, carries a risk of agranulocytosis, necessitating close monitoring of blood counts. Pimavanserin, a selective serotonin inverse agonist, avoids receptor-related side effects but has been linked to corrected QT (QTc) interval prolongation, while quetiapine has been reported to be associated with an increased risk of mortality. This review aims to analyze the benefits, risks, and mechanisms of action of antipsychotic medications to assist clinicians in making informed decisions and enhance patient care.

DRD4 VNTR 4/4 homozygosity as a genetic biomarker for treatment selection in patients with schizophrenia.

OBJECTIVE: There seems to be an association between the DRD4 48-bp VNTR polymorphisms and antipsychotic treatment response, but there is a rare reference to confirm this finding. Hence, the present study tried to investigate the association between DRD4 48-bp VNTR polymorphisms and the treatment response of antipsychotics in patients with schizophrenia in Taiwan, using a propensity score matching (PSM) method. METHODS: A total of 882 participants were enrolled in this study and completed informed consent, research questionnaires, including demographic information and the revised Chinese version Beliefs about Voices Questionnaire, and blood sampling. For descreasing of the selection bias and confounding variables, the PSM nearest neighbor matching method was used to select 765 paitents with schizophrenia (ratio of 1:8 between 85 persistent auditory hallucination and 680 controls) with matched and controlled the age and gender. RESULTS: Schizophrenia patients with DRD4 4 R homozygosity had a lower rate of good antipsychotic treatment response than the other DRD4 genotype carriers (DRD4 non-4/4). Among those 4 R homozygosity carriers, 60 cases of 503 (11.9%) retain persistent auditory hallucinations. Furthermore, this subgroup of patients is accounted for up to 70.6% of cases with poor neuroleptic treatment response. CONCLUSIONS: A poor treatment outcome for patients with the 4 R homozygosity had presented,that comparing with those DRD non-4/4 genotype carriers. DRD4 VNTR 4 R homozygosity could be a genetic biomarker to predict poor antipsychotic treatment response in schizophrenia. Patients with DRD 4/4 probably receive novel antipsychotic medications preferentially or in combination with alternative therapy, such as psychotherapy or milieu therapy.

Pimavanserin Treatment for Psychosis in Patients with Dementia with Lewy Bodies: A Case Series.

BACKGROUND Many patients with dementia with Lewy bodies (DLB) experience cholinesterase inhibitor- and antipsychotic-resistant psychosis. The new second-generation antipsychotic pimavanserin has been used with some success in the treatment of psychosis in other forms of dementia, including Alzheimer disease and Parkinson disease dementia. It is possible that pimavanserin may also be useful in the treatment of psychosis in DLB. We sought to describe the disease course and treatment of psychosis in 4 patients with DLB who were prescribed pimavanserin after other medications failed to reduce the frequency or severity of hallucinations and delusions. CASE REPORT This is a case series of 4 male patients (ages 56 to 74 at the beginning of the reports) who developed DLB and psychosis (eg, visual illusions, visual and olfactory hallucinations, and paranoid delusions). All 4 patients were prescribed cholinesterase inhibitors (eg, donepezil or rivastigmine) prior to pimavanserin, and only 1 patient experienced improved psychosis while on cholinesterase inhibitors. All 3 patients who were prescribed first-generation antipsychotics (eg, haloperidol) or traditional second-generation antipsychotics (eg, olanzapine, risperidone, or quetiapine) experienced initial or lasting side effects with no improvement of psychosis. Conversely, all 4 patients tolerated pimavanserin well, and 3 of the 4 patients experienced significant improvement of psychosis (eg, fewer hallucinations, fewer delusions, reduced paranoia, and/or reduced distress or agitation related to hallucinations and delusions) when prescribed pimavanserin. CONCLUSIONS This case series suggests that pimavanserin is tolerable in older males with DLB and that it may be useful for the reduction of distressful hallucinations, delusions, and paranoia in patients with DLB.

The Risk of Neuropsychiatric Adverse Events With Use of Leukotriene Receptor Antagonists in Patients With Asthma: Analysis of Korea's National Health Insurance Sharing Service Database.

BACKGROUND: Montelukast, a selective leukotriene receptor antagonist, is a commonly prescribed allergy medication but its potential association with neuropsychiatric adverse events is concerning. OBJECTIVE: To analyze Korea's National Health Insurance System claims records to identify the risk of neuropsychiatric adverse events in patients with asthma treated with montelukast. METHODS: This retrospective population-based study analyzed the National Health Insurance claims records of the entire Korean population between 2008 and 2015. We compared the risk of neuropsychiatric adverse events among patients with asthma using inhaled corticosteroids and/or long-acting ß2-agonists with montelukast or pranlukast and those not using leukotriene receptor antagonists (control group). RESULTS: There was no increased risk of the composite outcome of all measured neuropsychiatric adverse events in patients with asthma who were prescribed montelukast or pranlukast compared with those who were not. However, montelukast use was associated with an increased risk of hallucinations (inverse probability treatment weighting hazard ratio, 1.45; 95% CI, 1.07-1.96) and attention problems (inverse probability treatment weighting hazard ratio, 1.24; 95% CI, 1.01-1.52). Significant negative hazards for disorientation, anxiety, stress reactions, and somatic symptoms were observed in the montelukast group. When grouped by sex, the risk of hallucinations and attention problems was higher in men prescribed montelukast compared with the controls. CONCLUSIONS: We did not observe an increase in all neuropsychiatric adverse events in the leukotriene receptor antagonist-treated group; however, an increased risk of hallucinations and attention problems was observed in those taking montelukast, regardless of the medication administration period.

Cholinesterase Inhibitors for Delusions and Hallucinations in Alzheimer Disease and Parkinson Disease: Questionably Significant Benefits.

Delusions and hallucinations are common in Alzheimer disease (AD) and Parkinson disease (PD), especially in the later stages of illness. Antipsychotic drugs are effective in treating these psychotic symptoms but are associated with an increased risk of serious adverse events, including mortality. There is therefore a need to explore other treatment approaches. In this context, a recent individual patient data meta-analysis of 17 randomized controlled trials (RCTs) conducted in AD (12 RCTs) and PD (5 RCTs) found that the cholinesterase inhibitor (ChEI) drugs donepezil, rivastigmine, and galantamine attenuated the severity of both delusions and hallucinations in both AD and PD. Most of these trials were 24 weeks in duration. The effect sizes, expressed as standardized mean differences (SMDs), were, however, small, lying in the -0.08 to -0.14 range. These values are so small as to be perhaps clinically insignificant. When analyses were restricted to data from patients who actually had delusions and hallucinations at baseline, all effect sizes became larger, lying in the -0.13 to -0.39 range; however, after correcting for multiple hypothesis testing, only the finding for delusions in PD remained statistically significant. The meta-analysis did not provide information on what the best doses were, how long it took for improvement to become evident, and what proportion of patients showed remission from psychotic symptoms. Whereas the signal identified in this meta-analysis merits examination in appropriately designed RCTs, the findings of the meta-analysis may not much change current treatment strategies because patients with dementia would probably anyway receive a ChEI. Therefore, if psychotic symptoms persist for 24 weeks despite optimally dosed ChEI treatment, and if behavioral and psychosocial interventions do not help, clinicians may need to consider the potential benefits vs risks of other drugs, such as atypical antipsychotics and pimavanserin, in a shared decision-making process.

Amantadine toxicity causing visual hallucinations.

Amantadine is an N-methyl-d-aspartate receptor agonist with secondary dopaminergic activity that is used to treat Parkinson's disease-related dyskinesia and to treat fatigue in multiple sclerosis. It is primarily renally excreted and so impaired kidney function prolongs its half-life and may lead to toxicity. We describe a woman with multiple sclerosis taking amantadine who developed acute renal impairment, which triggered florid visual hallucinations that resolved on stopping the medication.

Cholinesterase Inhibitors for Treatment of Psychotic Symptoms in Alzheimer Disease and Parkinson Disease: A Meta-analysis.

Importance: Psychotic symptoms greatly increase the burden of disease for people with neurodegenerative disorders and their caregivers. Cholinesterase inhibitors (ChEIs) may be effective treatment for psychotic symptoms in these disorders. Previous trials only evaluated neuropsychiatric symptoms as a secondary and an overall outcome, potentially blurring the outcomes noted with ChEI use specifically for psychotic symptoms. Objective: To quantitatively assess the use of ChEIs for treatment of individual neuropsychiatric symptoms, specifically hallucinations and delusions, in patients with Alzheimer disease (AD), Parkinson disease (PD), and dementia with Lewy bodies (DLB). Data Sources: A systematic search was performed in PubMed (MEDLINE), Embase, and PsychInfo, without year restrictions. Additional eligible studies were retrieved from reference lists. The final search cutoff date was April 21, 2022. Study Selection: Studies were selected if they presented the results of placebo-controlled randomized clinical trials, including at least 1 donepezil, rivastigmine, or galantamine treatment arm in patients with AD, PD, or DLB; if they applied at least 1 neuropsychiatric measure including hallucinations and/or delusions; and if a full-text version of the study was available in the English language. Study selection was performed and checked by multiple reviewers. Data Extraction and Synthesis: Original research data were requested on eligible studies. A 2-stage meta-analysis was then performed, using random-effects models. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed for extracting data and assessing the data quality and validity. Data extraction was checked by a second reviewer. Main Outcomes and Measures: Primary outcomes were hallucinations and delusions; secondary outcomes included all other individual neuropsychiatric subdomains as well as the total neuropsychiatric score. Results: In total, 34 eligible randomized clinical trials were selected. Individual participant data on 6649 individuals (3830 [62.6%] women; mean [SD] age, 75.0 [8.2] years) were obtained from 17 trials (AD: n = 12; PD: n = 5; individual participant data were not available for DLB). An association with ChEI treatment was shown in the AD subgroup for delusions (-0.08; 95% CI, -0.14 to -0.03; P = .006) and hallucinations (-0.09; 95% CI, -0.14 to -0.04; P = .003) and in the PD subgroup for delusions (-0.14; 95% CI, -0.26 to -0.01; P = .04) and hallucinations (-0.08, 95% CI -0.13 to -0.03; P = .01). Conclusions and Relevance: The results of this individual participant data meta-analysis suggest that ChEI treatment improves psychotic symptoms in patients with AD and PD with small effect sizes.

[Pimavanserin and trazodone combination in behavioral disorders in severe dementia with Lewy bodies]. / Association pimavansérine et trazodone dans les troubles du comportementde la maladie à corps de Lewy sévère.

INTRODUCTION: Dementia with Lewy bodies (DLB) is characterized by neurocognitive disorders associated with core clinical features including hallucinations. There is currently no cure but a combination of symptomatic treatments: clozapine is commonly used in DLB-related psychosis. Pimavanserin is a serotonin 5HT-2A receptor inverse agonist that has recently been shown to reduce psychosis related to dementia. Trazodone is a serotonin reuptake inhibitor and a 5-HT2 receptor antagonist: it is effective in the treatment of the frontal syndrome and is commonly used in frontotemporal degeneration. PATIENTS AND METHODS: We describe three patients with DLB, hospitalized in the cognitive-behavioral unit of the University Hospitals of Strasbourg, who presented with major visual hallucinations, delusion, and an orbitofrontal syndrome including disinhibition, agitation, and irritability. The 3 patients were intolerant of low-dose Clozapine (neutropenia for one, somnolence for the other and Pisa syndrome and falls for the last one). We evaluated the Neuropsychiatric Inventory (NPI) before and after the introduction of both treatments. RESULTS: Given their psychotic and frontal symptoms, we used Pimavanserin and Trazodone simultaneously. After 4 to 6 weeks of treatment, a marked improvement was observed in all 3 patients, with a decrease of the NPI scores from a mean of 88 to 38. DISCUSSION AND CONCLUSION: To our knowledge, there is no previously described combination of these two treatments in DLB. A clinical trial combining these two molecules against pervasive behavioral disorders in DLB would be interesting in view of these preliminary results.

[Contribution of serotonin 5-HT2A receptor to antidepressant effect of serotonergic psychedelics].

Major depressive disorder presents a substantial global health burden, and at least 30-40% of patients exhibit treatment resistance to antidepressants. Ketamine, an NMDA receptor antagonist, is used as an anesthetic agent. In 2019, the U.S. Food and Drug Administration (FDA) approved esketamine (the S-enantiomer of ketamine) as a therapeutic agent for treatment-resistant depression; however, this drug has reportedly been associated with serious side effects such as dissociative symptoms, thus limiting its clinical use as an antidepressant. Recently, various clinical studies have reported that psilocybin, the psychoactive substance found in magic mushrooms, has a fast-acting and long-lasting antidepressant effect in patients with major depressive disorder, including those resistant to conventional treatment. Furthermore, psilocybin is a psychoactive drug that is relatively harmless compared to ketamine and other similar substances. Accordingly, the FDA has designated psilocybin as a "breakthrough therapy approach" for the treatment of major depressive disorder. Additionally, serotonergic psychedelics such as psilocybin and lysergic acid diethylamide show some potential in the treatment of depression, anxiety, and addiction. The increased attention the use of psychedelics has attracted as a psychiatric disorder treatment approach is referred to as the "psychedelic renaissance". Pharmacologically, psychedelics cause hallucinations by stimulating cortical serotonin 5-HT2A receptors (5-HT2A), although whether 5-HT2A is responsible for the manifestation of their therapeutic effects remains unclear. Furthermore, it is unclear whether the hallucinations and "mystical experience" that the patients go through because of 5-HT2A activation by psychedelics is essential for the therapeutic effect of these substances. Future research should elucidate the molecular and neural mechanisms underlying the therapeutic effects of psychedelics. This review summarizes the therapeutic effects of psychedelics on psychiatric disorders such as major depressive disorder in clinical and pre-clinical studies, and discusses the possibility of 5-HT2A as a novel therapeutic target.

Delirium secondary to anticholinergics.

We present a case of a young man who developed sudden deterioration in his physical and mental state whilst being treated as an inpatient for substance-induced psychosis. This deterioration was manifested by sudden disorientation, change in behaviour and visual hallucinations. It was only after excluding other potential causes that this presentation was attributed to the regular administration of procyclidine that was being used to counteract the extrapyramidal side effects from antipsychotics. The patient showed a dramatic improvement on stopping procyclidine. This case highlights the importance of awareness of rare adverse drug reactions and the resultant distressing effect for the patient himself.

Varenicline induced auditory hallucinations in a young female with bipolar disorder: a case report.

BACKGROUND: Creating appropriate and sustainable treatment plans for patients with concurrent disorders presents a challenge to psychiatrists and addiction medicine specialists alike. Although varenicline has been found to be the most effective medication for smoking cessation and abstinence when compared to results from placebo medications, nicotine patches and bupropion, caution is needed when starting patients on this medication. With the high prevalence of concurrent mental health and substance use disorders in vulnerably-housed populations in Canada, it becomes increasingly important to advocate for increased guidance and research into treating concurrent disorders. CASE PRESENTATION: In this case, a young female patient provisionally diagnosed with bipolar I disorder was hospitalized for a manic episode in the context of substance use and medication noncompliance. She also endorsed a long history of tobacco, alcohol, cocaine, cannabis and ketamine use. Perceptual abnormalities, including auditory hallucinations, were not recorded at admission. In addition to being stabilized for bipolar diagnosis, the patient was started on nicotine replacement therapy on Day 7 of admission followed by initiation of varenicline for smoking cessation on Day 14 of admission. Soon after the varenicline treatment was started, the patient developed auditory hallucinations, paranoia and referential beliefs. However, her insight was intact, and she had minimal thought form disorganization. In this case, these symptoms were thought to be secondary to varenicline after the consideration of potential alternative contributors. CONCLUSION: The occurrence of side effects as a result of varenicline use in patients with diagnosed mental health conditions is rare and underlying psychiatric illness is not labeled as an absolute contraindication in the prescription of varenicline. However, it is important to advocate for increased guidance and research on the treatment of substance use disorders in patients with bipolar I disorder. Patients may also benefit from increased collaboration between psychiatric and addiction services as that may allow for earlier recognition and intervention of symptoms to minimize distress.

The future of hallucination research: Can hallucinogens and psychedelic drugs teach us anything?

Hallucinations are one of the most interesting and least understood of all human experiences. This commentary addresses the ideas which most influenced my thinking in the past 20 years and what I believe to be the most currently promising area of enquiry. Interest in hallucinations reaches far back into antiquity and across cultures. The similarity of hallucinations in mental illness with the perceptual experiences reported by individuals who not mentally unwell has long been recognized. Early scientific research on hallucinogen drugs such as lysergic acid diethylamide (LSD) was criticized and then withdrawn, but its recent revival offers new opportunities to examine the mechanism and 'process' of hallucinating. Many psychedelic compounds can elicit intense and realistic hallucinations. The study of hallucinogens conducted in carefully controlled and supervised settings and with individuals who are not mentally unwell opens exciting new possibilities. For example, it may be possible to study the temporal shifts in perceptual awareness, decode what influences the contents, affect, meaning, and appraisals of hallucinations and guide novel psychotherapy techniques and drug therapy.

More than meets the eye: The role of sensory dimensions in psychedelic brain dynamics, experience, and therapeutics.

Psychedelics are undergoing a major resurgence of scientific and clinical interest. While multiple theories and frameworks have been proposed, there is yet no universal agreement on the mechanisms underlying the complex effects of psychedelics on subjective experience and brain dynamics, nor their therapeutic benefits. Despite being prominent in psychedelic phenomenology and distinct from those elicited by other classes of hallucinogens, the effects of psychedelics on low-level sensory - particularly visual - dimensions of experience, and corresponding brain dynamics, have often been disregarded by contemporary research as 'epiphenomenal byproducts'. Here, we review available evidence from neuroimaging, pharmacology, questionnaires, and clinical studies; we propose extensions to existing models, provide testable hypotheses for the potential therapeutic roles of psychedelic-induced visual hallucinations, and simulations of visual phenomena relying on low-level cortical dynamics. In sum, we show that psychedelic-induced alterations in low-level sensory dimensions 1) are unlikely to be entirely causally reconducible to high-level alterations, but rather co-occur with them in a dialogical interplay, and 2) are likely to play a causally relevant role in determining high-level alterations and therapeutic outcomes. We conclude that reevaluating the currently underappreciated role of sensory dimensions in psychedelic states will be highly valuable for neuroscience and clinical practice, and that integrating low-level and domain-specific aspects of psychedelic effects into existing nonspecific models is a necessary step to further understand how these substances effect both acute and long-term change in the human brain.

The socialization of hallucinations: Cultural priors, social interactions, and contextual factors in the use of psychedelics.

The effects of so-called "psychedelic" or "hallucinogenic" substances are known for their strong conditionality on context. While the so-called culturalist approach to the study of hallucinations has won the favor of anthropologists, the vectors by which the features of visual and auditory imagery are structured by social context have been so far little explored. Using ethnographic data collected in a shamanic center of the Peruvian Amazon and an anthropological approach dialoguing with phenomenology and recent models of social cognition of Bayesian inspiration, I aim to shed light on the nature of these dynamics through an approach I call the "socialization of hallucinations." Distinguishing two levels of socialization of hallucinations, I argue that cultural background and social interactions organize the relationship not only to the hallucinogenic experience, but also to its very phenomenological content. I account for the underpinnings of the socialization of hallucinations proposing such candidate factors as the education of attention, the categorization of perceptions, and the shaping of emotions and expectations. Considering psychedelic experiences in the light of their noetic properties and cognitive penetrability debates, I show that they are powerful vectors of cultural transmission. I question the ethical stakes of this claim, at a time when the use of psychedelics is becoming increasingly popular in the global North. I finally emphasize the importance of better understanding the extrapharmacological factors of the psychedelic experience and its subjective implications, and sketch out the basis for an interdisciplinary methodology in order to do so.