Won Sup Kim - Academia.edu (original) (raw)

Papers by Won Sup Kim

Journal of the Korean …, 2010

BACKGROUND: Cardiopulmonary resuscitation (CPR) can lead to various neurologic outcomes in patien... more BACKGROUND: Cardiopulmonary resuscitation (CPR) can lead to various neurologic outcomes in patients with hypoxicischemic encephalopathy (HIE). This study investigated the usefulness of clinical markers and electroencephalography (EEG) in predicting the neurologic ...

BMC Neuroscience, 2015

Figure 1 (A) A hierarchical modular network model 256-p-q-r, where p denotes the number of links ... more Figure 1 (A) A hierarchical modular network model 256-p-q-r, where p denotes the number of links of one node with nodes of its lower-level module, q links with nodes of the rest modules in its upper-level module, and r links with nodes of any modules from the rest of the network. Here we present an example of p = 13, q = 4 and r = 1. (B) Plot of the inverse phase synchronization index versus the number of links connecting two modules. The linear dependence between the inverse phase synchronization index and the number of links connecting two modules is shown when the local field potential is taken over m oscillators belonging to a subset of each module.

World Academy of Science, Engineering and Technology, International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering, 2012

We present on the method of inverse coherence matrix for the estimation of network connectivity f... more We present on the method of inverse coherence matrix for the estimation of network connectivity from multivariate time series of a complex system. In a model system of coupled chaotic oscillators, it is shown that the inverse coherence matrix defined as the inverse of cross coherence matrix is proportional to the network connectivity. Therefore the inverse coherence matrix could be used for the distinction between the directly connected links from indirectly connected links in a complex network. We compare the result of network estimation using the method of the inverse coherence matrix with the results obtained from the coherence matrix and the partial coherence matrix. Keywords—Chaotic oscillator, complex network, inverse coherence matrix, network estimation.

Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology, 2013

Spectral power analysis of VEPs in response to flash visual stimuli showed distinct spatiotempora... more Spectral power analysis of VEPs in response to flash visual stimuli showed distinct spatiotemporal characteristics recorded from visual cortices in epilepsy surgery patients with intracranial recordings.

Journal of clinical neurology (Seoul, Korea), 2013

Background and PurposezzRepetitive transcranial magnetic stimulation (rTMS) has potential as a no... more Background and PurposezzRepetitive transcranial magnetic stimulation (rTMS) has potential as a noninvasive neuromodulation treatment method for various neuropsychiatric disorders, and repeated sessions of rTMS are more likely to enhance the therapeutic efficacy. This study investigated neurophysiologic and spatiodynamic changes induced by repeated 1-Hz rTMS of the temporal cortex using transcranial magnetic stimulation (TMS) indices and fluorodeoxyglucose positron emission tomography (FDG-PET).

PloS one, 2013

Cortical physiology in human motor cortex is influenced by behavioral motor training (MT) as well... more Cortical physiology in human motor cortex is influenced by behavioral motor training (MT) as well as repetitive transcranial magnetic stimulation protocol such as intermittent theta burst stimulation (iTBS). This study aimed to test whether MT and iTBS can interact with each other to produce additive changes in motor cortical physiology. We hypothesized that potential interaction between MT and iTBS would be dependent on BDNF Val66Met polymorphism, which is known to affect neuroplasticity in the human motor cortex. Eighty two healthy volunteers were genotyped for BDNF polymorphism. Thirty subjects were assigned for MT alone, 23 for iTBS alone, and 29 for MT + iTBS paradigms. TMS indices for cortical excitability and motor map areas were measured prior to and after each paradigm. MT alone significantly increased the motor cortical excitability and expanded the motor map areas. The iTBS alone paradigm also enhanced excitability and increased the motor map areas to a slightly greater extent than MT alone. A combination of MT and iTBS resulted in the largest increases in the cortical excitability, and the representational motor map expansion of MT + iTBS was significantly greater than MT or iTBS alone only in Val/Val genotype. As a result, the additive interaction between MT and iTBS was highly dependent on BDNF Val66Met polymorphism. Our results may have clinical relevance in designing rehabilitative strategies that combine therapeutic cortical stimulation and physical exercise for patients with motor disabilities.

Europhysics Letters (epl), 2011

We investigated the possibility of estimating network link weights from the multivariate time ser... more We investigated the possibility of estimating network link weights from the multivariate time series of phase oscillators on a complex network. The inverse phase synchronization index of the coupled oscillator network is found to grow in proportion to the corresponding link weight, as network synchronization occurs for a strong coupling strength. This implies that the network link weights can be estimated from the measurement of the inverse phase synchronization indices. By adopting this estimation method, we successfully reconstructed the minimal spanning tree of the original network from the inverse phase synchronization indices. Even for the weak coupling case, the estimation of the network link weights could be improved significantly by taking the average of a sufficiently large number of configurations.

…, Jan 1, 2012

Electroencephalography amplitude, phase synchronization, and directionality of phase coupling wit... more Electroencephalography amplitude, phase synchronization, and directionality of phase coupling within and between hemispheres were compared for different frequency components in 27 healthy individuals before and after 5 days of daily 1 Hz repetitive transcranial magnetic stimulation (rTMS), and at 2 weeks after the last session. Instantaneous amplitudes of a (8-13 Hz) and b (13-30 Hz) frequency components were increased after daily rTMS, the effects of which were declining over time, suggesting an adapting response with repeated rTMS sessions. The phase synchronization of electroencephalography increased significantly in the a frequency, especially the upper-a band (11-13 Hz), in both the frontal and the temporal areas, predominantly in the ipsilateral hemisphere. Asymmetric directional interactions of the upper-a band were stronger from the stimulated area to the contralateral hemisphere. No significant differences were found at 2 weeks after rTMS in any of these values. Focal 1 Hz rTMS induces an enhancement in the ipsilateral dominant corticocortical interaction drastically by interhemispheric asymmetric coupling from the stimulated cortical area with an adapting response with repeated sessions. This kind of method can be valuable for possible clinical applications in various neuropsychiatric conditions to study the therapeutic mechanisms of 1 Hz rTMS. NeuroReport Patterns of PLV change (DPLV) after 1 Hz rTMS on the right temporal cortex. (a-d) d, y, a, and b bands. Top and middle panels: PLV changes for sham and active rTMS. DPLV values between all possible electrodes pairs are depicted by lines with different colors and widths. Black dots depict channel positions and the dashed black circle indicates the cortical location of rTMS application. Lower panels: 'Lt. Intra', 'Inter', and 'Rt. Intra' correspond to left intrahemispheric, interhemispheric, and right intrahemispheric connections. The asterisk (*) indicates significant differences at P less than 0.05. rTMS, repetitive transcranial magnetic stimulation.

Physical Review E, Jan 1, 1998

We propose a stochastic oscillator neural network model of the Hopfield-type memory for pattern s... more We propose a stochastic oscillator neural network model of the Hopfield-type memory for pattern segmentation tasks exploiting temporal dynamics of stochastic nonlinear oscillators. The nonlinear oscillators in the model are driven by subthreshold periodic force and noise. For an input pattern which is an overlapped superposition of several stored patterns, it is shown that the proposed model network is capable of segmenting out each pattern one after another as synchronous firings of a group of neurons. A systematic study of the dependence on the model parameters shows that the temporal segmentation attains its optimal performance at an intermediate noise intensity, which is reminiscent of the stochastic resonance observed in the coupled oscillator networks. It is also shown that the inhibitory coupling between oscillator groups representing different patterns plays an important role in that it enhances both the firing rate and the intergroup desynchrony that are essential requirements for the optimal performance of the temporal segmentation.

BMC Neuroscience, Jan 1, 2007

Recently the temporal coding based on spike timing is one of the hot issues in neuroscience. In t... more Recently the temporal coding based on spike timing is one of the hot issues in neuroscience. In the neural network, spike timing depends on the external stimulus and also on the internal network structure. In this study, we propose a method of inferring network connectivity from multiple spike trains. It is based on the phase model description of the spike trains. A continuous phase variable is introduced for each of the spike trains by assigning 2 pi phase for each of the spike intervals and by the linear interpolation. The relative strength of the mutual dependence allows us to estimate the relative strength of the coupling as well as the type of coupling. We report the results of our test on the coupled neural network model and also on the electronic circuit experiment. When compared with the conventional method based on the cross-correlogram, the proposed method is much more effective in estimating the network connectivity. At the same time, the measurement of the effective coupling allows us to estimate the type of coupling.

A stochastic oscillator neural network (STONN) model of the Hopfield-type memory is proposed for ... more A stochastic oscillator neural network (STONN) model of the Hopfield-type memory is proposed for the pattern segmentation tasks, that exploits temporal dynamics of the stochastic nonlinear oscillators. For an input pattern which is an overlapped superposition of several stored patterns the proposed model network is shown to be capable of segmenting out each pattern one after another as the network evolves its temporal dynamics. The temporal segmentation attains its optimal performance at an intermediate noise intensity and the performance becomes improved as the coupling strength between oscillators increases. A mechanism for the selective attention is also introduced in the STONN by controlling the level of noise applied to the most salient pattern and by adopting the inhibition-of-return into the patterns that have been segmented before

Neurocomputing, Jan 1, 2006

We perform phase analysis of the αα (8–13 Hz) and θθ (4–7 Hz) rhythmic components of the single-t... more We perform phase analysis of the αα (8–13 Hz) and θθ (4–7 Hz) rhythmic components of the single-trial electroencephalograms (EEGs), which comprise the most dominant contributions to the event-related potentials (ERPs). The oscillatory ERP patterns of two components are well described by the phase resetting and the inter-trial phase coherency. A method for the estimation of the nonlinear dynamic dependency between two components is proposed. According to the method, the coupling is asymmetric with the coupling from the θθ to the αα rhythms stronger than the reversed one.

International Journal of Bifurcation and Chaos, Jan 1, 2002

Decoding of a sequence of interspike intervals (ISIs) of a neuron model driven by a chaotic stimu... more Decoding of a sequence of interspike intervals (ISIs) of a neuron model driven by a chaotic stimulus is performed based on the attractor reconstruction method. As stimulus strength increases, both the stimulus estimation error and the prediction error in predicting stimulus crosswise by exploiting ISIs information tend to decrease with transitional drops at certain parameter values. It is analyzed that such behaviors are well explained in the context of synchronization between two chaotic patterns of stimulus and ISI sequence. The result implies that a new scheme of temporal coding at low firing rate regime can be achieved which exploits the preservation of nonlinear deterministic structures in stimulus.

Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society, Jan 1, 2010

The authors investigated the oscillatory changes induced by auditory language task to assess hemi... more The authors investigated the oscillatory changes induced by auditory language task to assess hemispheric dominance of language. Magnetoencephalography studies were conducted during word listening in 6 normal right-handed volunteers and 13 epilepsy patients who underwent Wada test. We carried out a time-frequency analysis of event-related desynchronization (ERD)/event-related synchronization (ERS) and intertrial coherence. We localized ERD/ERS on each subject's magnetic resonance images using beamformer. We compared ERD/ERS values between the left and right side of regions of interest in inferior frontal and superior temporal areas. We assessed the target frequency range that correlated best with the Wada test results. In all normal subjects, gamma ERD was lateralized to the left side in both the inferior frontal and superior temporal areas. In epilepsy patients, the concordance rate of gamma ERD and the Wada test results was 76.9% for the inferior frontal area and 69.2% for the superior temporal area. Gamma ERD can be considered as an indicator of language function, although it was not sufficient to replace the Wada test in the evaluation of epilepsy patients. The gamma ERD value of the inferior frontal area was more reliable for the assessment of language dominance compared with that obtained in the superior temporal area. FIGURE 3. Spatial mapping of gamma ERD/ERS of a sample case using the beamformer approach. Gamma ERD was prominent in the left inferior frontal area (crossmark). ERD, event-related desynchronization; ERS, event-related synchronization. Blue indicates ERD, and red indicates ERS. FIGURE 4. Gamma ERD/ERS of the inferior frontal and superior temporal ROIs of a sample case. We defined manually the ROIs (dotted lines) of the inferior frontal area (Brodmann areas 44 and 45) and of the posterior part of the superior temporal area (posterior part of Brodmann area 22)-areas that are homologous to the Broca and Wernicke areas-on individual brain surfaces. The gamma ERDs of the inferior frontal and posterior superior temporal areas were more prominent in the left hemisphere. ERD, event-related desynchronization; ERS, event-related synchronization; ROI, region of interest. Blue indicates ERD, and red indicates ERS.