Frontiers in Human Neuroscience
January 1, 2014
Robin Carhart‐Harris, Robert Leech, Peter J. Hellyer et al.
1,289 citations
Entropy, a measure of uncertainty or disorder, is applied to brain function and consciousness, focusing on the psychedelic state induced by psilocybin. The psychedelic state is considered a primary or primitive state of consciousness, characterized by elevated entropy in brain function, including a greater repertoire of functional connectivity motifs that form and fragment over time. This suggests primary states may exhibit criticality, a transition zone between order and disorder. Normal waking consciousness suppresses entropy, operating just below criticality, which constrains cognition and enables metacognitive functions like reality-testing and self-awareness. Entry into primary states involves collapse of default-mode network activity and decoupling from medial temporal lobes. These hypotheses can be tested by comparing brain activity in REM sleep, early psychosis, normal waking consciousness, and anesthesia.
Human Brain Mapping
July 3, 2014
Enzo Tagliazucchi, Robin Carhart‐Harris, Robert Leech et al.
423 citations
Psilocybin, the active compound in magic mushrooms, increases the variability and range of brain activity and connectivity. Using fMRI, fifteen healthy volunteers were scanned before, during, and after receiving psilocybin or a placebo. Psilocybin raised the variability of blood-oxygen-level-dependent signals in the hippocampi and anterior cingulate cortex. Changes in the spectral behavior of brain signals were limited to higher-order networks, including the default mode, executive control, and dorsal attention networks. The brain also explored a wider repertoire of connectivity states after psilocybin than under control conditions. These findings help explain the unconstrained, hyper-associative quality of consciousness in the psychedelic state.
Journal of The Royal Society Interface
January 1, 2016
Enzo Tagliazucchi, Dante R. Chialvo, Michael Siniatchkin et al.
210 citations
Loss of consciousness from propofol sedation reduces long-range temporal correlations in frontothalamic brain activity and weakens the link between functional connectivity and anatomical structure. A model based on phase transitions in complex systems reproduces these patterns and also explains the cortex's reduced sensitivity to external stimuli during unconsciousness. The findings suggest that these neural changes are universal across different causes of unconsciousness.
arXiv Preprint Archive
May 26, 2014
Enzo Tagliazucchi, Robin Carhart-Harris, Robert Leech et al.
Psilocybin, the active compound in magic mushrooms, dramatically expands the brain's repertoire of connectivity states, revealing how consciousness can be altered. Using advanced brain imaging, researchers tracked neural activity before and after psilocybin administration. Results showed increased signal variability in memory and emotion-processing regions, while higher brain networks displayed enhanced flexibility in their communication patterns.