Serotonergic psychedelics LSD & psilocybin increase the fractal dimension of cortical brain activity in spatial and temporal domains
Thomas F. Varley, Robin Carhart-Harris, Leor Roseman, David K. Menon, Emmanuel A. Stamatakis
Neuroimage June 30, 2020 DOI: 10.1016/j.neuroimage.2020.117049 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Experimental study Peer reviewed |
|---|---|
| Population | Volunteers under the influence of LSD and psilocybin |
| Interventions | LSD psilocybin |
| Topics | Psilocybin Serotonin LSD |
| Keywords | Fractal dimension Correlation dimension Consciousness Pattern recognition psychology Fractal analysis Artificial intelligence Hallucinogen Mathematical analysis |
| Citations | 91 |
| Key findings | Both LSD and psilocybin significantly increased the fractal dimension of functional connectivity networks, and LSD significantly increased the fractal dimension of BOLD signals, with psilocybin showing a non-significant trend in the same direction. |
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.
Comparable studies
Other experimental studies on LSD, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Neural correlates of the LSD experience revealed by multimodal neuroimaging. Human participants | 2016 | Experimental study | |
| Crystal structure of an LSD-bound human serotonin receptor | 2017 | Experimental study with structural biology and molecular dynamics simulations | |
| Lysergic Acid Diethylamide: Sensitive Neuronal Units in the Midbrain Raphe Midbrain neurons containing serotonin | 1968 | Experimental study | |
| Connectome-harmonic decomposition of human brain activity reveals dynamical repertoire re-organization under LSD. Human brain | 2017 | Experimental study | |
| LSD-Assisted Psychotherapy in Patients with Terminal Cancer Cancer patients | 1973 | Experimental study | n = 60 |
Citations in the library
Cited by 78
- REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics Pharmacological Reviews June 20, 2019
- Default Mode Network Modulation by Psychedelics: A Systematic Review The International Journal of Neuropsychopharmacology October 21, 2022
- LSD alters dynamic integration and segregation in the human brain. Neuroimage February 15, 2021
- Consciousness and complexity: a consilience of evidence Neuroscience of Consciousness 2021
- From Egoism to Ecoism: Psychedelics Increase Nature Relatedness in a State-Mediated and Context-Dependent Manner. International Journal of Environmental Research and Public Health December 16, 2019
and 73 more in the library
Cites 37
- Psilocybin can occasion mystical-type experiences having substantial and sustained personal meaning and spiritual significance Psychopharmacology July 7, 2006
- Consciousness as Integrated Information: a Provisional Manifesto Biological Bulletin December 1, 2008
- The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs Frontiers in Human Neuroscience 2014
- Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin Proceedings of the National Academy of Sciences January 23, 2012
- Neural correlates of the LSD experience revealed by multimodal neuroimaging. Proceedings of the National Academy of Sciences April 11, 2016
and 32 more in the library