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.
Anesthesiology
September 7, 2013
Heonsoo Lee, George A. Mashour, Gyu‐jeong Noh et al.
153 citations
General anesthesia with propofol reconfigures the brain's functional network hub structure and reverses the phase relationship between frontal and parietal regions. Using graph theoretical analysis of 21-channel electroencephalogram data from 10 volunteers, the study found that network topology—not connection strength—correlates with states of consciousness. After propofol administration, average path length, clustering coefficient, and modularity increased, long-range connections were disrupted, and hub node strength decreased. The primary hub shifted from parietal to frontal regions. The phase lead of frontal to parietal areas in the alpha frequency band (8-13 Hz) during wakefulness reversed direction after propofol and returned during recovery. Changes in network topology may be the primary mechanism for loss of frontal to parietal feedback during anesthesia.
PLoS Computational Biology
April 14, 2015
Joon-Young Moon, UnCheol Lee, Stefanie Blain‐moraes et al.
143 citations
Efficient brain networks balance global integration with functional specialization, but how global topology, local node dynamics, and information flow relate has been unclear. Using analytical solutions of oscillator models, computational simulations on model and anatomical brain networks, and high-density electroencephalography from conscious and anesthetized humans, the authors demonstrate that network nodes with more connections (higher degree) have larger amplitudes and are directional targets (phase lag) rather than sources (phase lead). This degree–directionality relationship appears to be a fundamental network property with direct applicability to brain function. Changes in directionality patterns across states of human consciousness are driven by alterations in brain network topology.
PLoS Computational Biology
August 30, 2018
Hyoungkyu Kim, Joon-Young Moon, George A. Mashour et al.
79 citations
Hysteresis—the difference between the forward and reverse paths of state transitions—occurs as people lose and regain consciousness. Analyzing high-density EEG from healthy volunteers given sevoflurane or ketamine, the authors found that functional brain networks exhibit hysteresis during these transitions. The principle of explosive synchronization, which governs abrupt state shifts in many complex networks, also explains hysteresis in the brain. More potent anesthetics produce larger hysteresis; a broader range of EEG frequencies hastens the loss of consciousness but delays its return; connectivity shows greater hysteresis than EEG power; and network structure and strength reconfigure differently during loss versus recovery. These results indicate that hysteresis in conscious state transitions is a generic network feature, potentially allowing prediction and modulation of such transitions.
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.
PLoS ONE
August 15, 2013
Jeongkyu Shin, George A. Mashour, Seungwoo Ku et al.
16 citations
General anesthesia rapidly alters brain network connectivity, and standard graph-theoretical methods that assume static networks are poorly suited to capture these changes. A new technique was introduced to track the temporal evolution of network modules. Multichannel EEG was recorded from 18 surgical patients anesthetized with propofol or sevoflurane. Networks were reconstructed by treating each EEG channel as a node and correlated activity between channels as a link. The frequency of subgraphs with a defined number of links was analyzed; subgraphs with high occurrence probability were called network "backbones." Constitutive, variable, and state-specific backbones were identified across consciousness, induction, maintenance, and recovery. This approach enables a granular, dynamic description of network evolution.
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.
Current biology : CB
July 2, 2026
Youngjai Park, Younghwa Cha, Hyoungkyu Kim et al.
The human brain's information flow alternates between two dominant modes roughly every 200 milliseconds: a top-down mode where anterior brain regions drive posterior activity, and a bottom-up mode with reverse directionality. These sub-second alternations are most prominent during wakefulness, gradually diminish under anesthesia, and show pathological imbalance in attention-deficit/hyperactivity disorder (ADHD). Simultaneous EEG-fMRI recordings reveal that top-down dynamics coincide with increased activity in higher-order cognitive networks, while bottom-up dynamics correspond to heightened sensory network activity. A connectome-based coupled-oscillator model reproduces these transitions, suggesting they emerge naturally from structural connectivity. Relative phase analysis (RPA) enables tracking these whole-brain dynamics with millisecond precision in real time from electroencephalography.
bioRxiv : the preprint server for biology
March 28, 2025
Youngjai Park, Younghwa Cha, Hyoungkyu Kim et al.
preprint
The human brain shifts between two directional modes on a sub-second timescale: a top-down mode where anterior regions drive posterior activity and a bottom-up mode with reverse directionality. These shifts are most distinct during full consciousness and become less pronounced as awareness fades. Simultaneous EEG-fMRI recordings show the top-down mode coincides with higher-order cognitive network activity, while the bottom-up mode aligns with sensory system activity. An inattentive ADHD cohort exhibited imbalances in these transition dynamics compared to typically developing individuals. A coupled-oscillator model of the structural brain network reproduced these patterns, suggesting they arise naturally from inter-regional neural interactions.
Frontiers in Systems Neuroscience
December 1, 2021
Minkyung Kim, Hyoungkyu Kim, Zirui Huang et al.
The brain's ability to switch between internal and external modes is crucial for generating models of self and world, and this switching may rely on a state near criticality—a balanced condition between order and disorder. Large synchronization fluctuations of brain networks near criticality create temporal windows that favor either integrating internal information or processing external stimuli. Using computational modeling, EEG, and fMRI analyses across altered states of consciousness, synchronized networks bias toward internal information while incoherent networks bias toward external information. These preferences are most prominent at criticality and in conscious states associated with 4–12 Hz bandwidth.
NeuroImage
March 1, 2019
Heonsoo Lee, D. Golkowski, D. Jordan et al.
Large-scale brain networks function near a critical state, and partial phase locking—a network science concept—shapes the characteristic functional connectivity and asymmetric anterior-posterior phase lag entropy (PLE) topography at this critical state, with low PLE for high-degree nodes and high PLE for low-degree nodes. Comparing PLE topography at criticality with electroencephalogram data from baseline consciousness, isoflurane anesthesia, ketamine anesthesia, vegetative state/unresponsive wakefulness syndrome, and minimally conscious state shows that topographical similarity and strength of PLE differentiate these pharmacologic and pathologic states of consciousness. This provides a theory-based metric to quantify how far a perturbed brain network deviates from criticality, rather than merely determining critical or non-critical state.
Frontiers in Human Neuroscience
February 16, 2018
Hyoungkyu Kim, A. Hudetz, Joseph Lee et al.
A practical method estimates integrated information (Φ), a measure proposed by integrated information theory to be related to consciousness, from 128-channel EEG. The method alone cannot distinguish certain anesthetic states, but combining Φ with four EEG connectivity parameters—power, frequency, functional connectivity, and modularity—differentiates all states of consciousness. The association of Φ with EEG connectivity during anesthesia offers a new approach to applying the theory, potentially useful for characterizing consciousness in sleep, anesthesia, and coma.