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.
PLoS Computational Biology
January 20, 2011
Adam B. Barrett, Anil K. Seth
243 citations
Two new measures of integrated information, Φ(E) and Φ(AR), overcome limitations of the earlier Φ(DM) measure, which could rarely be applied to biological systems because it required discrete Markov dynamics. The new measures are easy to apply to time-series data, as demonstrated through simulations. They offer new opportunities for studying information integration in real and model systems and have implications for understanding consciousness and other neurocognitive processes. However, the findings also challenge theories that assign physical meaning to these measured quantities.
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.
Trends in Cognitive Sciences
June 1, 2022
Pedro A. M. Mediano, Fernando E. Rosas, Daniel Bor et al.
109 citations
The integrated information theory of consciousness (IIT) proposes a universal mathematical formula derived from fundamental properties of conscious experience to describe the quality of consciousness. The theory is ambitious in that it aims to derive a mathematical measure of integrated information from consciousness itself, using properties of conscious experience to characterize the quality of consciousness. The text repeatedly states that IIT is a theory of consciousness that proposes a mathematical formula derived from fundamental properties of conscious experience to describe the quality of consciousness, but it does not provide specific findings, numbers, or empirical results.
Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences
May 23, 2022
Pedro A. M. Mediano, Fernando E. Rosas, Andrea I. Luppi et al.
73 citations
Emergence—how galaxies form or consciousness arises from neurons—lacks formal tools for rigorous study. This article summarizes, elaborates, and extends a recent formal theory of causal emergence based on information decomposition, which is quantifiable and empirically testable. The theory links emergence to information about a system's temporal evolution that cannot be obtained from its parts separately. The article provides an accessible but rigorous introduction to this framework, discussing its merits in various scenarios, interpretation issues, and potential misunderstandings, highlighting the distinctive benefits of this formalism.
bioRxiv (Cold Spring Harbor Laboratory)
November 2, 2020
Pedro A. M. Mediano, Fernando E. Rosas, Christopher Timmermann et al.
39 citations
preprint
Psychedelics reliably increase brain entropy (neural signal diversity), an effect linked to psychological changes and opposite to the decrease seen during loss of consciousness. This study investigated how context—specifically stimulus manipulation—modulates that entropy increase. Participants under LSD or placebo experienced eyes-closed versus eyes-open conditions, or no stimulus, music, or video. Brain entropy rose with LSD across all conditions but was largest with eyes closed. Entropy changes consistently matched subjective ratings of the psychedelic experience, except during video viewing, suggesting competition between external stimuli and internal LSD-induced imagery. The findings provide quantitative evidence that context shapes neural dynamics during psychedelic experiences, supporting the practice of eyes-closed psychedelic psychotherapy, and challenge simplistic views of brain entropy as a direct measure of conscious level.
Frontiers in Human Neuroscience
July 3, 2014
Cassandra Gould van Praag, Tom Froese, Adam B. Barrett et al.
29 citations
A detailed phenomenological investigation of sequence-space synesthesia in a single adult (AB) reveals that synesthetic experiences occur within a specific spatial reference frame, a 'mental room' that overlays perception of the physical world, and that AB can voluntarily switch attention between these two rooms. Using the Elicitation Interview method across 9 hours of transcripts, the study found that, contrary to AB's initial report, the synesthetic concurrents usually followed an internal verbalization of the inducer rather than visual presentation, indicating an auditory component. This suggests cross-modal interactions between auditory and visual systems in the development of this synesthetic form.
bioRxiv
December 7, 2023
Joseph Starkey, Robin L. Carhart-Harris, Andrea Pigorini et al.
preprint
A measure of 'statistical complexity' that calculates the diversity of statistical interactions in neural activity, removing randomness, was tested on human brain data from different sleep stages and from people under ketamine, LSD, and psilocybin. Statistical complexity differentiated sleep stages similarly to the standard Lempel-Ziv complexity measure and increased relative to placebo for all three psychedelic substances. The measure is a useful alternative for investigating neural activity complexity across states of consciousness.
arXiv Preprint Archive
April 13, 2026
Adam B. Barrett, Borjan Milinkovic, Pedro A. M. Mediano et al.
The integrated information theory of consciousness (IIT) proposes a mathematical formula, derived from fundamental properties of conscious experience, to describe the quantity and quality of consciousness for any physical system. This article clarifies common misunderstandings. A high value of the measure Φ does not mean 'more consciousness'; Φ might be replaced with a suite of quantities for a multidimensional characterization. IIT implies a distinct panpsychism where space and time are tiled with substrates of proto-consciousness, which the authors find unproblematic. Φ is not well-defined for real physical systems and has never been computed on one; only proxies have been computed, not approximations. For IIT to align with fundamental physics, a reformulation in continuous fields would be needed.
arXiv Preprint Archive
February 25, 2025
Romy Beauté, David J. Schwartzman, Guillaume Dumas et al.
Stroboscopic light stimulation on closed eyes typically induces simple visual hallucinations—vivid, geometric, and colorful patterns. An analysis of 862 open-ended reports from the Dreamachine immersive experience, using large language models and topic modeling, confirmed these simple hallucinations and also revealed altered states of consciousness and complex hallucinations. This computational approach enables systematic study of subjective experiences beyond standard questionnaires, capturing subtle patterns not readily identified through closed-form questions. The findings broaden understanding of stroboscopically induced phenomena and demonstrate the potential of natural language processing in computational neurophenomenology.
arXiv Preprint Archive
February 12, 2019
Adam B. Barrett, Pedro A. M. Mediano
Integrated Information Theory (IIT) defines consciousness as a fundamental property of physical systems, measured by the quantity Phi. For IIT to be credible, Phi must be uniquely defined and always well-defined. This article identifies three ways in which the current formulation of Phi fails these standards, making the measure ambiguous or ill-defined in certain cases, and discusses potential solutions to address these foundational issues.
arXiv Preprint Archive
July 3, 2014
Adam B. Barrett
Consciousness may arise from information intrinsic to fundamental electromagnetic fields, according to a hypothesis that unites fundamental physics with empirical neuroscience. The proposal extends Integrated Information Theory, which says consciousness comes from intrinsic information generated by dynamical systems, but which existing formulations cannot apply to standard physical models. By treating electromagnetic fields as fundamental, the hypothesis bypasses the need for quantum effects while aligning with known neural correlates of consciousness. This approach aims to eliminate dualistic 'ghosts' by describing consciousness as an aspect of the physical world.