OPEN Foundation

R. Carhart-Harris

Hallucinations Under Psychedelics and in the Schizophrenia Spectrum: An Interdisciplinary and Multiscale Comparison

Abstract

The recent renaissance of psychedelic science has reignited interest in the similarity of drug-induced experiences to those more commonly observed in psychiatric contexts such as the schizophrenia-spectrum. This report from a multidisciplinary working group of the International Consortium on Hallucinations Research (ICHR) addresses this issue, putting special emphasis on hallucinatory experiences. We review evidence collected at different scales of understanding, from pharmacology to brain-imaging, phenomenology and anthropology, highlighting similarities and differences between hallucinations under psychedelics and in the schizophrenia-spectrum disorders. Finally, we attempt to integrate these findings using computational approaches and conclude with recommendations for future research.

Leptourgos, P., Fortier-Davy, M., Carhart-Harris, R., Corlett, P. R., Dupuis, D., Halberstadt, A. L., Kometer, M., Kozakova, E., LarØi, F., Noorani, T. N., Preller, K. H., Waters, F., Zaytseva, Y., & Jardri, R. (2020). Hallucinations Under Psychedelics and in the Schizophrenia Spectrum: An Interdisciplinary and Multiscale Comparison. Schizophrenia bulletin, 46(6), 1396–1408. https://doi.org/10.1093/schbul/sbaa117

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A mechanistic model of the neural entropy increase elicited by psychedelic drugs

Abstract

Psychedelic drugs, including lysergic acid diethylamide and other agonists of the serotonin 2A receptor (5HT2A-R), induce drastic changes in subjective experience, and provide a unique opportunity to study the neurobiological basis of consciousness. One of the most notable neurophysiological signatures of psychedelics, increased entropy in spontaneous neural activity, is thought to be of relevance to the psychedelic experience, mediating both acute alterations in consciousness and long-term effects. However, no clear mechanistic explanation for this entropy increase has been put forward so far. We sought to do this here by building upon a recent whole-brain model of serotonergic neuromodulation, to study the entropic effects of 5HT2A-R activation. Our results reproduce the overall entropy increase observed in previous experiments in vivo, providing the first model-based explanation for this phenomenon. We also found that entropy changes were not uniform across the brain: entropy increased in some regions and decreased in others, suggesting a topographical reconfiguration mediated by 5HT2A-R activation. Interestingly, at the whole-brain level, this reconfiguration was not well explained by 5HT2A-R density, but related closely to the topological properties of the brain’s anatomical connectivity. These results help us understand the mechanisms underlying the psychedelic state and, more generally, the pharmacological modulation of whole-brain activity.

Herzog, R., Mediano, P., Rosas, F. E., Carhart-Harris, R., Perl, Y. S., Tagliazucchi, E., & Cofre, R. (2020). A mechanistic model of the neural entropy increase elicited by psychedelic drugs. Scientific reports, 10(1), 17725. https://doi.org/10.1038/s41598-020-74060-6

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DMT alters cortical travelling waves

Abstract

Psychedelic drugs are potent modulators of conscious states and therefore powerful tools for investigating their neurobiology. N,N, Dimethyltryptamine (DMT) can rapidly induce an extremely immersive state of consciousness characterized by vivid and elaborate visual imagery. Here, we investigated the electrophysiological correlates of the DMT-induced altered state from a pool of participants receiving DMT and (separately) placebo (saline) while instructed to keep their eyes closed. Consistent with our hypotheses, results revealed a spatio-temporal pattern of cortical activation (i.e. travelling waves) similar to that elicited by visual stimulation. Moreover, the typical top-down alpha-band rhythms of closed-eyes rest were significantly decreased, while the bottom-up forward wave was significantly increased. These results support a recent model proposing that psychedelics reduce the ‘precision-weighting of priors’, thus altering the balance of top-down versus bottom-up information passing. The robust hypothesis-confirming nature of these findings imply the discovery of an important mechanistic principle underpinning psychedelic-induced altered states.

Alamia, A., Timmermann, C., Nutt, D. J., VanRullen, R., & Carhart-Harris, R. L. (2020). DMT alters cortical travelling waves. eLife, 9, e59784. https://doi.org/10.7554/eLife.59784

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Positive effects of psychedelics on depression and wellbeing scores in individuals reporting an eating disorder

Abstract

Purpose: Psychedelic therapy is showing promise for a broad range of mental health conditions, indicative of a transdiagnostic action. While the efficacy of symptom-focused treatments for eating disorders (EDs) is limited, improved mental health and psychological wellbeing are thought to contribute to greater treatment outcomes. This study provides the first quantitative exploration of the psychological effects of psychedelics in those reporting an ED diagnosis.

Methods: Prospective, online data were collected from individuals planning to take a psychedelic drug. Twenty-eight participants reporting a lifetime ED diagnosis completed measures of depressive symptomology (Quick Inventory of Depressive Symptomology; QIDS-SR16) and psychological wellbeing (Warwick-Edinburgh Mental Wellbeing Scale; WEMWBS) 1-2 weeks before, and 2 weeks after a psychedelic experience. Twenty-seven of these participants also completed a measure of emotional breakthrough [Emotional Breakthrough Inventory (EBI)] in relation to the acute psychedelic experience.

Results: Bayesian t tests demonstrated overwhelming evidence for improvements in depression and wellbeing scores following the psychedelic experience. Marginal evidence was also found for a correlation between emotional breakthrough and the relevant mental health improvements.

Conclusion: These findings provide supportive evidence for positive psychological aftereffects of a psychedelic experience that are relevant to the treatment of EDs. It is hoped that this will encourage further research and will bolster initiatives to directly examine the safety and efficacy of psychedelic assisted therapy as a treatment of EDs in future clinical trials.

Level of evidence: Level III, cohort study.

Spriggs, M. J., Kettner, H., & Carhart-Harris, R. L. (2021). Positive effects of psychedelics on depression and wellbeing scores in individuals reporting an eating disorder. Eating and weight disorders : EWD, 26(4), 1265–1270. https://doi.org/10.1007/s40519-020-01000-8

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Post-Psychedelic Reductions in Experiential Avoidance Are Associated With Decreases in Depression Severity and Suicidal Ideation

Abstract

Psychedelic therapy shows promise as a novel intervention for a wide range of mental health concerns but its therapeutic action is incompletely understood. In line with acceptance and commitment therapy’s (ACT’s) transdiagnostic model, qualitative research has suggested that reductions in experiential avoidance are an important component of therapeutic outcomes associated with psychedelics. However, limited research has quantitatively explored the association between decreases in experiential avoidance and therapeutic outcomes associated with psychedelics. Therefore, in two prospective studies, using convenience samples of individuals with plans to use a psychedelic, we explored the impact of psychedelic use on experiential avoidance, depression severity, and suicidal ideation, as well as relationships between changes in these outcomes. Participants (Study 1, N=104; Study 2, N=254) completed self-report questionnaires of depression severity, suicidal ideation, and experiential avoidance: 1) before using a psychedelic (in ceremonial and non-ceremonial contexts), as well as 2) 2-weeks and 3) 4-weeks after psychedelic use. Across both studies, repeated measures ANOVAs indicated significant decreases in experiential avoidance, depression severity, and suicidal ideation after psychedelic use. Furthermore, decreases in experiential avoidance were significantly associated with decreases in depression severity and suicidal ideation. These results suggest that psychedelics may lead to significant decreases in experiential avoidance, depression severity, and suicidal ideation. Additionally, these findings imply that reduced experiential avoidance may be a transdiagnostic mechanism mediating treatment success within psychedelic therapy. We conclude that integrating psychedelics with psychotherapeutic interventions that target experiential avoidance (e.g. ACT) may enhance therapeutic outcomes.

Zeifman, R. J., Wagner, A. C., Watts, R., Kettner, H., Mertens, L. J., & Carhart-Harris, R. L. (2020). Post-Psychedelic Reductions in Experiential Avoidance Are Associated With Decreases in Depression Severity and Suicidal Ideation. Frontiers in psychiatry, 11, 782. https://doi.org/10.3389/fpsyt.2020.00782

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The Current Status of Psychedelics in Psychiatry

Abstract

In the 1950s, the Swiss pharmaceutical company Sandoz, which employed the chemist Albert Hofmann, who discovered lysergic acid diethylamide (LSD) and the similar serotonergic psychedelic psilocybin, made these drugs available to the psychiatric research community as the products Delysid and Indocybin, respectively. By the 1960s, these drugs had caused a revolution in brain science and psychiatry because of their widespread use by researchers and clinicians in many Western countries, especially the US. Before LSD was banned, the US National Institutes of Health funded more than 130 studies exploring its clinical utility, with positive results in a range of disorders but particularly anxiety, depression, and alcoholism. However, the displacement of LSD into recreational use and eventual association with the anti-Vietnam war movement led to all psychedelics being banned in the US. This ban became ratified globally under the 1971 UN Convention on narcotics. Since then, research funding, drug production, and the study of psychedelics as clinical agents has been virtually stopped. Until very recently, no companies would manufacture medical-grade psychedelics, which made getting regulatory approval for clinical research—especially clinical trials—very difficult and in some countries (eg, Germany) impossible.

Nutt, D., & Carhart-Harris, R. (2021). The current status of psychedelics in psychiatry. JAMA psychiatry78(2), 121-122.; 10.1001/jamapsychiatry.2020.2171
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Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatial and temporal domains

Abstract

Psychedelic drugs, such as psilocybin and LSD, represent unique tools for researchers investigating the neural origins of consciousness. Currently, the most compelling theories of how psychedelics exert their effects is by increasing the complexity of brain activity and moving the system towards a critical point between order and disorder, creating more dynamic and complex patterns of neural activity. While the concept of criticality is of central importance to this theory, few of the published studies on psychedelics investigate it directly, testing instead related measures such as algorithmic complexity or Shannon entropy. We propose using the fractal dimension of functional activity in the brain as a measure of complexity since findings from physics suggest that as a system organizes towards criticality, it tends to take on a fractal structure. We tested two different measures of fractal dimension, one spatial and one temporal, using fMRI data from volunteers under the influence of both LSD and psilocybin. The first was the fractal dimension of cortical functional connectivity networks and the second was the fractal dimension of BOLD time-series. In addition to the fractal measures, we used a well-established, non-fractal measure of signal complexity and show that they behave similarly. We were able to show that both psychedelic drugs significantly increased the fractal dimension of functional connectivity networks, and that LSD significantly increased the fractal dimension of BOLD signals, with psilocybin showing a non-significant trend in the same direction. With both LSD and psilocybin, we were able to localize changes in the fractal dimension of BOLD signals to brain areas assigned to the dorsal-attenion network. These results show that psychedelic drugs increase the fractal dimension of activity in the brain and we see this as an indicator that the changes in consciousness triggered by psychedelics are associated with evolution towards a critical zone.

Varley, T. F., Carhart-Harris, R., Roseman, L., Menon, D. K., & Stamatakis, E. A. (2020). Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatial and temporal domains. NeuroImage220, 117049; 10.1016/j.neuroimage.2020.117049
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Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatial and temporal domains

Abstract

Psychedelic drugs, such as psilocybin and LSD, represent unique tools for researchers investigating the neural origins of consciousness. Currently, the most compelling theories of how psychedelics exert their effects is by increasing the complexity of brain activity and moving the system towards a critical point between order and disorder, creating more dynamic and complex patterns of neural activity. While the concept of criticality is of central importance to this theory, few of the published studies on psychedelics investigate it directly, testing instead related measures such as algorithmic complexity or Shannon entropy. We propose using the fractal dimension of functional activity in the brain as a measure of complexity since findings from physics suggest that as a system organizes towards criticality, it tends to take on a fractal structure. We tested two different measures of fractal dimension, one spatial and one temporal, using fMRI data from volunteers under the influence of both LSD and psilocybin. The first was the fractal dimension of cortical functional connectivity networks and the second was the fractal dimension of BOLD time-series. In addition to the fractal measures, we used a well-established, non-fractal measure of signal complexity and show that they behave similarly. We were able to show that both psychedelic drugs significantly increased the fractal dimension of functional connectivity networks, and that LSD significantly increased the fractal dimension of BOLD signals, with psilocybin showing a non-significant trend in the same direction. With both LSD and psilocybin, we were able to localize changes in the fractal dimension of BOLD signals to brain areas assigned to the dorsal-attenion network. These results show that psychedelic drugs increase the fractal dimension of activity in the brain and we see this as an indicator that the changes in consciousness triggered by psychedelics are associated with evolution towards a critical zone.

Varley, T. F., Carhart-Harris, R., Roseman, L., Menon, D. K., & Stamatakis, E. A. (2020). Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatial and temporal domains. NeuroImage220, 117049; 10.1016/j.neuroimage.2020.117049
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Spotlight commentary: REBUS and the anarchic brain

Abstract

In ‘REBUS and the Anarchic Brain: Towards a Unified Model of the Brain Action of Psychedelics’, Carhart-Harris and Friston offer an important analysis of what the predictive processing framework has to offer our understanding of psychedelic experiences, providing an invaluable ground for psychedelic psychiatry. While applauding this, we encourage paying greater attention to contextual factors shaping extreme experiences and their sequalae, and suggest that the authors’ comparisons with certain non-psychedelic altered states may overlook more informative parallels that can be drawn elsewhere. Addressing both points will prove fruitful, ultimately, in identifying the mechanisms of action of greatest interest in psychedelic experiences.
Carhart-Harris, R. L., & Friston, K. J. (2019). REBUS and the anarchic brain: toward a unified model of the brain action of psychedelics. Pharmacological reviews71(3), 316-344., https://doi.org/10.1093/nc/niaa007
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Dynamic coupling of whole-brain neuronal and neurotransmitter systems

Abstract

Remarkable progress has come from whole-brain models linking anatomy and function. Paradoxically, it is not clear how a neuronal dynamical system running in the fixed human anatomical connectome can give rise to the rich changes in the functional repertoire associated with human brain function, which is impossible to explain through long-term plasticity. Neuromodulation evolved to allow for such flexibility by dynamically updating the effectivity of the fixed anatomical connectivity. Here, we introduce a theoretical framework modeling the dynamical mutual coupling between the neuronal and neurotransmitter systems. We demonstrate that this framework is crucial to advance our understanding of whole-brain dynamics by bidirectional coupling of the two systems through combining multimodal neuroimaging data (diffusion magnetic resonance imaging [dMRI], functional magnetic resonance imaging [fMRI], and positron electron tomography [PET]) to explain the functional effects of specific serotoninergic receptor (5-HT2AR) stimulation with psilocybin in healthy humans. This advance provides an understanding of why psilocybin is showing considerable promise as a therapeutic intervention for neuropsychiatric disorders including depression, anxiety, and addiction. Overall, these insights demonstrate that the whole-brain mutual coupling between the neuronal and the neurotransmission systems is essential for understanding the remarkable flexibility of human brain function despite having to rely on fixed anatomical connectivity.

 
Kringelbach, M. L., Cruzat, J., Cabral, J., Knudsen, G. M., Carhart-Harris, R., Whybrow, P. C., … & Deco, G. (2020). Dynamic coupling of whole-brain neuronal and neurotransmitter systems. Proceedings of the National Academy of Sciences117(17), 9566-9576., https://doi.org/10.1073/pnas.1921475117
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