Hyoungkyu Kim's research while affiliated with Korea University and other places
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Publications (15)
To the Editor—With great interest, we read the recent study by Tanabe et al. (1), which demonstrated reduced electroencephalographic (EEG) complexity, assessed via the Lempel-Ziv algorithm (2), during postoperative delirium. The study results also revealed a negative correlation between global Lempel-Ziv complexity and delirium severity in broadban...
Delirium is a major public health issue associated with considerable morbidity and mortality, particularly after surgery. While the neurobiology of delirium remains incompletely understood, emerging evidence suggests that cognition requires close proximity to a system state called criticality , which reflects a point of dynamic instability that all...
Continuous switching between internal and external modes in the brain appears important for generating models of the self and the world. However, how the brain transitions between these two modes remains unknown. We propose that a large synchronization fluctuation of brain networks, emerging only near criticality (i.e., a balanced state between ord...
Psychedelics have been recognized as model interventions for studying altered states of consciousness. However, few empirical studies of the shamanic state of consciousness, which is anecdotally similar to the psychedelic state, exist. We investigated the neural correlates of shamanic trance using high-density electroencephalography (EEG) in 24 sha...
Continuous switching between internal and external modes in the brain is a key process of constructing inner models of the outside world. However, how the brain continuously switches between two modes remains elusive. Here, we propose that a large synchronization fluctuation of the brain network emerging only near criticality (i.e., a balanced stat...
Despite the use of shamanism as a healing practice for several millennia, few empirical studies of the shamanic state of consciousness exist. We investigated the neural correlates of shamanic trance using high-density electroencephalography (EEG) in 24 shamanic practitioners and 24 healthy controls during rest, shamanic drumming, and classical musi...
Integrated information theory (IIT) postulates that consciousness arises from the cause-effect structure of a system but the optimal network conditions for this structure have not been elucidated. In the study, we test the hypothesis that network criticality, a dynamically balanced state between a large variation of functional network configuration...
The network thresholding and the number of isolated nodes.
We tested the number of isolated nodes with increase of threshold in the construction of binary network. The threshold (0.1) was chosen to avoid isolated nodes in the EEG network in the baseline states (red dotted line).
(TIF)
Hysteresis, the discrepancy in forward and reverse pathways of state transitions, is observed during changing levels of consciousness. Identifying the underlying mechanism of hysteresis phenomena in the brain will enhance the ability to understand, monitor, and control state transitions related to consciousness. We hypothesized that hysteresis in b...
The significance levels of trajectory areas among frequency bands in ketamine experiment.
The one-way ANOVA was applied and Tukey-Kramer correction was used for the multiple comparisons. (*P < 0.05, **P < 0.01, and ***P < 0.001).
(XLSX)
The analytic derivations and the descriptions about S1 Fig, S1 Table, and S2 Table.
We analytically derived the relationship between anesthetic pharmacodynamics and the oscillator models in section 1, and also derived the extended oscillator model for the network hysteresis in section 2 and 3. The descriptions of figure and tables are in section 4...
The significance levels of trajectory areas among frequency bands in sevoflurane experiment.
The one-way ANOVA was applied and Tukey-Kramer correction was used for the multiple comparisons. (*P < 0.05, **P < 0.01, and ***P < 0.001).
(XLSX)
The integrated information theory (IIT) proposes a quantitative measure, denoted as Φ, of the amount of integrated information in a physical system, which is postulated to have an identity relationship with consciousness. IIT predicts that the value of Φ estimated from brain activities represents the level of consciousness across phylogeny and func...
Background:
Previous studies have demonstrated inconsistent neurophysiologic effects of ketamine, although discrepant findings might relate to differences in doses studied, brain regions analyzed, coadministration of other anesthetic medications, and resolution of the electroencephalograph. The objective of this study was to characterize the dose-...
Citations
... Substudy analyses from this trial also revealed that caffeine improves cortical dynamics supporting cognition. 17 These findings have not yet been corroborated by other perioperative clinical trials, as prior trials have not focused on delirium as the primary outcome. ...
... These advantages include large computational capability with temporal correlation (memory) and long-range correlation (efficient brain integration), high flexibility to adapt to a changing environment from scale-invariance, and wide repertoires of brain states from large fluctuations. Therefore, recent studies have proposed brain criticality as a necessary condition for the emergence of consciousness, and deviations from the critical state (i.e., after a transition to one of the possible states in a sub-or supercritical state) are hypothesized to give rise to ASC (Kim and Lee, 2019;Lee et al., 2019;Kim M. et al., 2021). ...
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... We focused on this group to investigate aspects of the neural basis of this effect. A neutral hypnosis without semantic suggestions had no effect on thresholds but caused a reduction of phase-locking synchronization (PLV) of the beta (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) frequency band between left and right hemispheric medial frontal cortex (MFC) and the finger representation (CP3, CP4) in somatosensory cortex (SI), which remained reduced across all hypnotic conditions. Late SEP Figure 5. Correlation between changes of tactile discrimination and changes of paired-pulse ratios. ...
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... Additionally, we would like to thank Kate Durda and Stephanie Tighe, who offered invaluable insight as shamanic practitioners when designing our study. This manuscript has been released as a pre-print at bioRxiv (Huels et al., 2020). ...
... It remains an open question whether hysteresis effects as described in (Kim et al. 2018) for ketamine and sevo urane anesthesia can be found in EEG microstate data under propofol. Our statistical analysis between the sedation depths labeled by (Chennu et al. 2016) revealed no signi cant differences between baseline and recovery, that is induction of and emergence from anesthesia. ...
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... Applying the IIT formula to such a system yields Φ infinite which is unfeasible result. It also requires explosivecomputational for estimating the Φ value for a real system, this makes its application to be impractical for the brain [89], [101].The other criticismis the lack of empirical evidence for its formulation, non-functionalism, unclear quantification of consciousness, and definition of consciousness [90], [91], [102]. However, recently there has been an attempt to resolve the computational cost of IIT by the use of searching algorithms for minimum information partition and measuring Φ from high-density electroencephalography [101], [103].The successful of this attempt is expected to increase the applicability of the theory. ...
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... subanesthetic ketamine in humans generally includes an increase of gamma oscillation power and a decrease of delta, alpha, and beta oscillation power 7,[12][13][14] . Oscillatory power changes have also been reported in patients with depression and have been used to differentiate depressive from healthy subjects 15 . ...
