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Search Results: 1 - 10 of 25279 matches for " Heekyung Lee "
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Targeting Neural Synchrony Deficits is Sufficient to Improve Cognition in a Schizophrenia-Related Neurodevelopmental Model
Heekyung Lee,Dino Dvorak,André A. Fenton
Frontiers in Psychiatry , 2014, DOI: 10.3389/fpsyt.2014.00015
Abstract: Cognitive symptoms are core features of mental disorders but procognitive treatments are limited. We have proposed a “discoordination” hypothesis that cognitive impairment results from aberrant coordination of neural activity. We reported that neonatal ventral hippocampus lesion (NVHL) rats, an established neurodevelopmental model of schizophrenia, have abnormal neural synchrony and cognitive deficits in the active place avoidance task. During stillness, we observed that cortical local field potentials sometimes resembled epileptiform spike-wave discharges with higher prevalence in NVHL rats, indicating abnormal neural synchrony due perhaps to imbalanced excitation–inhibition coupling. Here, within the context of the hypothesis, we investigated whether attenuating abnormal neural synchrony will improve cognition in NVHL rats. We report that: (1) inter-hippocampal synchrony in the theta and beta bands is correlated with active place avoidance performance; (2) the anticonvulsant ethosuximide attenuated the abnormal spike-wave activity, improved cognitive control, and reduced hyperlocomotion; (3) ethosuximide not only normalized the task-associated theta and beta synchrony between the two hippocampi but also increased synchrony between the medial prefrontal cortex and hippocampus above control levels; (4) the antipsychotic olanzapine was less effective at improving cognitive control and normalizing place avoidance-related inter-hippocampal neural synchrony, although it reduced hyperactivity; and (5) olanzapine caused an abnormal pattern of frequency-independent increases in neural synchrony, in both NVHL and control rats. These data suggest that normalizing aberrant neural synchrony can be beneficial and that drugs targeting the pathophysiology of abnormally coordinated neural activities may be a promising theoretical framework and strategy for developing treatments that improve cognition in neurodevelopmental disorders such as schizophrenia.
Emergence of Physiological Oscillation Frequencies in a Computer Model of Neocortex
Samuel A. Neymotin,Heekyung Lee,William W. Lytton
Frontiers in Computational Neuroscience , 2011, DOI: 10.3389/fncom.2011.00019
Abstract: Coordination of neocortical oscillations has been hypothesized to underlie the “binding” essential to cognitive function. However, the mechanisms that generate neocortical oscillations in physiological frequency bands remain unknown. We hypothesized that interlaminar relations in neocortex would provide multiple intermediate loops that would play particular roles in generating oscillations, adding different dynamics to the network. We simulated networks from sensory neocortex using nine columns of event-driven rule-based neurons wired according to anatomical data and driven with random white-noise synaptic inputs. We tuned the network to achieve realistic cell firing rates and to avoid population spikes. A physiological frequency spectrum appeared as an emergent property, displaying dominant frequencies that were not present in the inputs or in the intrinsic or activated frequencies of any of the cell groups. We monitored spectral changes while using minimal dynamical perturbation as a methodology through gradual introduction of hubs into individual layers. We found that hubs in layer 2/3 excitatory cells had the greatest influence on overall network activity, suggesting that this subpopulation was a primary generator of theta/beta strength in the network. Similarly, layer 2/3 interneurons appeared largely responsible for gamma activation through preferential attenuation of the rest of the spectrum. The network showed evidence of frequency homeostasis: increased activation of supragranular layers increased firing rates in the network without altering the spectral profile, and alteration in synaptic delays did not significantly shift spectral peaks. Direct comparison of the power spectra with experimentally recorded local field potentials from prefrontal cortex of awake rat showed substantial similarities, including comparable patterns of cross-frequency coupling.
Remote Gaze Tracking System on a Large Display
Hyeon Chang Lee,Won Oh Lee,Chul Woo Cho,Su Yeong Gwon,Kang Ryoung Park,Heekyung Lee,Jihun Cha
Sensors , 2013, DOI: 10.3390/s131013439
Abstract: We propose a new remote gaze tracking system as an intelligent TV interface. Our research is novel in the following three ways: first, because a user can sit at various positions in front of a large display, the capture volume of the gaze tracking system should be greater, so the proposed system includes two cameras which can be moved simultaneously by panning and tilting mechanisms, a wide view camera (WVC) for detecting eye position and an auto-focusing narrow view camera (NVC) for capturing enlarged eye images. Second, in order to remove the complicated calibration between the WVC and NVC and to enhance the capture speed of the NVC, these two cameras are combined in a parallel structure. Third, the auto-focusing of the NVC is achieved on the basis of both the user’s facial width in the WVC image and a focus score calculated on the eye image of the NVC. Experimental results showed that the proposed system can be operated with a gaze tracking accuracy of ±0.737°~±0.775° and a speed of 5~10 frames/s.
Differential Equation and Recursive Formulas of Sheffer Polynomial Sequences
Heekyung Youn,Yongzhi Yang
ISRN Discrete Mathematics , 2011, DOI: 10.5402/2011/476462
Decoherence Effects in Reactive Scattering
Heekyung Han,Paul Brumer
Physics , 2005, DOI: 10.1063/1.1879912
Abstract: Decoherence effects on quantum and classical dynamics in reactive scattering are examined using a Caldeira-Leggett type model. Through a study of dynamics of the collinear H+H2 reaction and the transmission over simple one-dimensional barrier potentials, we show that decoherence leads to improved agreement between quantum and classical reaction and transmission probabilities, primarily by increasing the energy dispersion in a well defined way. Increased potential nonlinearity is seen to require larger decoherence in order to attain comparable quantum-classical agreement.
Analytic solution to N vs. M photon phase control in an open two-level system
Heekyung Han,Paul Brumer
Physics , 2005, DOI: 10.1016/j.cplett.2005.02.094
Abstract: Decoherence effects on the traditional N vs. M photon coherent control of a two-level system are investigated, with 1 vs. 3 used as a specific example. The problem reduces to that of a two-level system interacting with a single mode field, but with an effective Rabi frequency that depends upon the fundamental and third harmonic fields. The resultant analytic control solution is explored for a variety of parameters, with emphasis on the dependence of control on the relative phase of the lasers. The generalization to off-resonant cases is noted.
Mutation Rates of TGFBR2 and ACVR2 Coding Microsatellites in Human Cells with Defective DNA Mismatch Repair
Heekyung Chung, Dennis J. Young, Claudia G. Lopez, Thuy-Anh T. Le, Jeffrey K. Lee, Deena Ream-Robinson, Sherry C. Huang, John M. Carethers
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003463
Abstract: Microsatellite instability promotes colonic tumorigenesis through generating frameshift mutations at coding microsatellites of tumor suppressor genes, such as TGFBR2 and ACVR2. As a consequence, signaling through these TGFβ family receptors is abrogated in DNA Mismatch repair (MMR)-deficient tumors. How these mutations occur in real time and mutational rates of these human coding sequences have not previously been studied. We utilized cell lines with different MMR deficiencies (hMLH1?/?, hMSH6?/?, hMSH3?/?, and MMR-proficient) to determine mutation rates. Plasmids were constructed in which exon 3 of TGFBR2 and exon 10 of ACVR2 were cloned +1 bp out of frame, immediately after the translation initiation codon of an enhanced GFP (EGFP) gene, allowing a ?1 bp frameshift mutation to drive EGFP expression. Mutation-resistant plasmids were constructed by interrupting the coding microsatellite sequences, preventing frameshift mutation. Stable cell lines were established containing portions of TGFBR2 and ACVR2, and nonfluorescent cells were sorted, cultured for 7–35 days, and harvested for flow cytometric mutation detection and DNA sequencing at specific time points. DNA sequencing revealed a ?1 bp frameshift mutation (A9 in TGFBR2 and A7 in ACVR2) in the fluorescent cells. Two distinct fluorescent populations, M1 (dim, representing heteroduplexes) and M2 (bright, representing full mutants) were identified, with the M2 fraction accumulating over time. hMLH1 deficiency revealed 11 (5.91×10?4) and 15 (2.18×10?4) times higher mutation rates for the TGFBR2 and ACVR2 microsatellites compared to hMSH6 deficiency, respectively. The mutation rate of the TGFBR2 microsatellite was ~3 times higher in both hMLH1 and hMSH6 deficiencies than the ACVR2 microsatellite. The ?1 bp frameshift mutation rates of TGFBR2 and ACVR2 microsatellite sequences are dependent upon the human MMR background.
Distinguishability and Chiral Stability: Effects of Decoherence and Intermolecular Interactions
Heekyung Han,David M. Wardlaw
Physics , 2010,
Abstract: We examine the effect of decoherence and intermolecular interactions (chiral discrimination energies) on the chiral stability and the distinguishability of initially pure versus mixed states in an open chiral system. Under a two-level approximation for a system, intermolecular interactions are introduced by a mean-field theory, and interaction between a system and an environment is modeled by a continuous measurement of a population difference between the two chiral states. The resultant equations are explored for various parameters, with emphasis on the combined effects of the initial condition of the system, the chiral discrimination energy and the decoherence. We focus on factors affecting the distinguishability as measured by population difference between the initially pure and mixed states and on the chiral stability as measured by the purity decay.
Effects of initial coherence on distinguishability of pure/mixed states and chiral stability in an open chiral system
Heekyung Han,David M. Wardlaw
Physics , 2010,
Abstract: We examine how initial coherences in open chiral systems affect distinguishability of pure versus mixed states and purity decay. Interaction between a system and an environment is modeled by a continuous position measurement and a two-level approximation is taken for the system. The resultant analytical solution is explored for various parameters, with emphasis on the interplay of initial coherences of the system and dephasing rate in determining the purity decay and differences in the time evolution of pure vs. mixed initial states. %the distinguishability and the decoherence process. Implications of the results on several fundamental problems are noted.
The impact of dose of the angiotensin-receptor blocker valsartan on the post-myocardial infarction ventricular remodeling: study protocol for a randomized controlled trial
Young-Rak Cho, Young-Dae Kim, Tae-Ho Park, Kyungil Park, Jong-Sung Park, Heekyung Baek, Sun-Young Choi, Kee-Sik Kim, Taek-Jong Hong, Tae-Hyun Yang, Jin-Yong Hwang, Jong-Seon Park, Seung-Ho Hur, Sang-Gon Lee
Trials , 2011, DOI: 10.1186/1745-6215-12-247
Abstract: Valsartan in post-MI remodeling (VALID) is a randomized, open-label, single-blinded multicenter study designed to compare the efficacy of different clinical dose of valsartan on the post-MI ventricular remodeling. This study also aims to assess neurohormone change and clinical parameters of patients during the post-infarct period. A total of 1116 patients with left ventricular dysfunction following the first episode of acute ST-elevation MI are to be enrolled and randomized to a maximal tolerable dose (up to 320 mg/day) or usual dose (80 mg/day) of valsartan for 12 months in 2:1 ratio. Echocardiographic analysis for quantifying post-MI ventricular remodeling is to be conducted in central core laboratory. Clinical assessment and laboratory test are performed at fixed times.VALID is a multicenter collaborative study to evaluate the impact of dose of valsartan on the post-MI ventricular remodeling. The results of the study provide information about optimal dosing of the drug in the management of patients after MI. The results will be available by 2012.NCT01340326Progressive enlargement of the heart chamber and deterioration of contractile function after myocardial infarction (MI), termed post-MI ventricular remodeling, is associated with development of heart failure and poor prognosis [1-3]. The magnitude of post-MI remodeling is influenced by several determinants, most notably infarct size [4], but also by ventricular wall stress [5], patency of infarct-related artery [6], and a number of neurohormonal factors [7]. Thus, the consequence of post-MI remodeling varies among patients with acute MI even in the era of reperfusion therapy [8]. Modification of neurohormonal acitivities, particularly the rennin-angiotensin-aldosterone system (RAAS), can significantly influence the process of ventricular remodeling after acute MI. Suppression of angiotensin activity either by inhibition of angiotensin-converting enzyme (ACE) [9-11] or by blockade of angiotensin II receptor [12]
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