Scientific Reports
April 19, 2017
Michael Schartner, Robin Carhart‐Harris, Adam B. Barrett et al.
450 citations
Measures of neural signal diversity, such as entropy and Lempel-Ziv complexity, are higher during wakeful rest than during anesthesia. In this study, these measures were computed for spontaneous magnetoencephalographic signals from humans under psilocybin, ketamine, and LSD. All three psychedelics produced reliably higher signal diversity, even after controlling for spectral changes, with the most pronounced increase in temporal (single-channel LZ complexity) rather than spatial diversity. Selective correlations emerged between changes in signal diversity and the intensity of psychedelic experience. This is the first time these measures have been applied to the psychedelic state and have yielded values exceeding normal waking consciousness, suggesting that psychedelic phenomenology constitutes an elevated level of consciousness.
Sci Rep
November 19, 2019
Christopher Timmermann, Leor Roseman, Michael Schartner et al.
325 citations
Intravenous DMT, a fast-acting psychedelic, markedly reduces alpha and beta brain wave power and increases spontaneous signal diversity in the human brain, as measured by EEG. The emergence of delta and theta oscillatory activity correlates with the peak of the subjective experience, especially its eyes-closed visual component. Relationships between changes in subjective experience and brain activity were observed across time, linking specific brain changes to specific aspects of the experience.
Neuroscience of Consciousness
January 27, 2017
Michael Schartner, Andrea Pigorini, Steve A. Gibbs et al.
158 citations
During non-rapid eye movement (NREM) sleep, neural dynamical complexity—measured by Lempel-Ziv complexity, amplitude coalition entropy, and synchrony coalition entropy—decreased substantially across broadly distributed brain regions in ten epilepsy patients. This decrease partially reversed during late-night NREM sleep and returned to wakeful rest levels during rapid eye movement (REM) sleep. Local brain regions mirrored this global pattern. The frontal lobe showed elevated signal complexity. These changes were not solely due to spectral power differences. The findings suggest that level of consciousness correlates with neural dynamical complexity.
bioRxiv (Cold Spring Harbor Laboratory)
January 4, 2019
David J. Schwartzman, Michael Schartner, Benjamin B. Ador et al.
31 citations
preprint
Stroboscopic stimulation—flashing light—can induce altered states of consciousness without drugs, increasing the intensity and range of subjective experiences, including simple and complex visual hallucinations. These experiences were accompanied by rises in EEG signal diversity, measured by Lempel-Ziv complexity, that exceeded levels seen during wakeful rest. The results align with previous findings from psychedelic studies and support the idea that neural signal diversity reflects the richness of subjective experience across different states of consciousness.
Neuroscience of Consciousness
January 1, 2020
Michael Schartner, Christopher Timmermann
17 citations
The serotonergic system regulates the balance between prior expectations and sensory information in shaping conscious visual perception. Psychedelic drugs like N,N-Dimethyltryptamine can perturb this system, altering how the brain gates internal and external inputs. Two generative deep neural networks are discussed as tools to both illustrate the visual effects of psychedelics and to model the biological mechanisms of sensory gating. This approach offers a new medium, alongside paintings and verbal reports, for understanding how the brain constructs conscious experience.
Frontiers in psychology
January 1, 2018
Michał Bola, Paweł Orłowski, Karolina Baranowska et al.
11 citations
Brain signal diversity is a marker of consciousness, being lower in unconscious states and higher during psychedelic states. This study tested whether increasing the information rate of speech would increase signal diversity, reflecting richer experience. Nineteen participants listened to an audiobook at five speeds (65–135% of original) and to backward (unintelligible) speech, plus a resting-state condition. EEG Lempel-Ziv diversity was measured. The main hypothesis was not supported: Bayes Factor showed evidence for no effect of speech speed on diversity. Resting-state diversity was greater than during any speech condition. Diversity also gradually declined over the experiment, possibly due to decreasing vigilance, suggesting that unconstrained rest allows more varied experiences like mind wandering.
bioRxiv
July 18, 2019
Christopher Timmermann, Leor Roseman, Michael Schartner et al.
4 citations
preprint
Intravenous DMT, a fast-acting psychedelic, markedly alters human brain activity. Compared with a placebo, DMT reduced oscillatory power in alpha and beta brainwaves and increased spontaneous signal diversity. Time-referenced analyses linked changes in subjective experience to changes in brain activity. Emergence of delta and theta frequency oscillations correlated with the peak of the experience, particularly its eyes-closed visual component. These findings advance understanding of the neurobiological underpinnings of immersive states of consciousness.