Anesthesiology
May 22, 2013
UnCheol Lee, Seungwoo Ku, Gyu‐jeong Noh et al.
436 citations
Ketamine, like propofol and sevoflurane, inhibits feedback (anterior-to-posterior) connectivity between frontal and parietal brain regions after loss of consciousness, while preserving feedforward (posterior-to-anterior) connectivity. In 30 surgical patients given intravenous ketamine (2 mg/kg), electroencephalography showed that feedback connectivity gradually diminished and was significantly reduced after loss of consciousness (mean baseline 0.0074 vs. anesthesia 0.0055). Feedforward connectivity remained unchanged. Ketamine reduced alpha power and increased gamma power, unlike propofol and sevoflurane. Despite molecular and neurophysiologic differences, diverse anesthetics disrupt frontal-parietal communication, suggesting that directional connectivity analysis could provide a common metric for general anesthesia.
Frontiers in Human Neuroscience
March 18, 2021
Emma R. Huels, Hyoungkyu Kim, UnCheol Lee et al.
51 citations
Shamanic practitioners in trance show brain changes that overlap with but are distinct from those caused by psychedelic drugs. In 24 practitioners and 24 controls, EEG recordings during shamanic drumming revealed increased gamma power linked to visual changes, decreased low alpha and increased low beta connectivity, reduced gamma-band signal diversity tied to insightfulness, and increased criticality in beta and gamma bands correlating with complex imagery. Practitioners' altered-state scores matched or exceeded those of people on psychedelics. The findings indicate that shamanic trance and psychedelic states share some phenomenal features but produce unique neural signatures.
Frontiers in Systems Neuroscience
May 25, 2023
Charles Gervais, Louis-Philippe Boucher, Guillermo Martinez Villar et al.
25 citations
The healthy conscious brain is thought to operate near a critical state, balancing order and chaos for optimal information processing. This scoping review of 49 studies across seven altered states of consciousness (ASC)—including disorders of consciousness, sleep, anesthesia, epilepsy, psychedelics, delirium, and meditation—found that each category showed a deviation from this critical state. Most studies could identify a deviation but not its direction; however, a preliminary consensus indicates non-REM sleep reflects a subcritical state, epileptic seizures a supercritical state, and psychedelics are closer to criticality than normal waking consciousness. The evidence is limited and methodologically varied, but criticality may become an objective way to characterize ASC and guide treatments, such as using anesthesia or psychedelics to restore criticality in pathological brain states.
Translational Psychiatry
March 25, 2025
Brian H Silverstein, Nicholas Kolbman, Amanda Nelson et al.
8 citations
Psilocybin alters brain network organization in rats in a dose-dependent manner. Using electroencephalography from 27 cortical sites in 12 rats, the study found that psilocybin disrupted theta-gamma coupling, increased frontal high gamma connectivity and network density, and increased posterior theta connectivity and density. Medium gamma frontoparietal connectivity and behavioral activity showed an inverted-U relationship with dose. These results suggest that high-frequency network organization, decoupled from local theta-phase, may be a key signature of psilocybin-induced altered states of consciousness.
Anesthesiology
June 1, 2024
George A Mashour, UnCheol Lee, Dinesh Pal et al.
8 citations
Near-death experiences have been reported since antiquity and often involve perceptions of light, interactions with entities, and life recall. After in-hospital cardiac arrest, such experiences occur in 10 to 20% of cases. Recent neurophysiologic evidence suggests a surge of gamma oscillations and increased cortical connectivity following cardiac and respiratory arrest, offering a biological basis for this conscious experience.
bioRxiv (Cold Spring Harbor Laboratory)
February 12, 2024
Brian H Silverstein, Nicholas Kolbman, Amanda Nelson et al.
3 citations
preprint
Psilocybin disrupts the coupling between theta and gamma brain waves in rats and reorganizes brain networks in a dose-dependent manner. Using 27 electrodes across the cortex, the study found that psilocybin increased frontal high gamma connectivity and posterior theta connectivity, as well as network density in those regions. Medium gamma frontoparietal connectivity showed a nonlinear relationship with dose. Theta-gamma phase-amplitude coupling was disrupted. These changes suggest that high-frequency network organization, decoupled from local theta-phase, may be a signature of the altered state of consciousness induced by psilocybin.