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.
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.
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.