Dalkwon Koh

Yonsei University, Seoul, Seoul, South Korea

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Publications (6)10.48 Total impact

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    ABSTRACT: We studied depth-dependent cerebral hemodynamic responses of rat brain following direct cortical electrical stimulation (DCES) in vivo with optical recording of intrinsic signal (ORIS) and near-infrared spectroscopy (NIRS). ORIS is used to visualize the immediate hemodynamic changes in cortical areas following the stimulation, whereas NIRS measures the hemodynamic changes originating from subcortical areas. We found strong hemodynamic changes in relation to DCES both in ORIS and NIRS data. In particular, the signals originating from cortical areas exhibited a tri-phasic response, whereas those originating from subcortical regions exhibited multi-phasic responses. In addition, NIRS signals from two different sets of source-detector separation were compared and analyzed to investigate the causality of perfusion, which demonstrated downstream propagation, indicating that the upper brain region reacted faster than the deep region.
    Optics Express 03/2012; 20(7):6932-43. · 3.55 Impact Factor
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    ABSTRACT: In this study, a custom-manufactured 8-channel continuous-wave near-infrared spectroscopy (CWNIRS) system was used in combination with a single-unit recording device to simultaneously measure hemodynamic and neuronal activities in the somatosensory cortex of rats. Since the single-unit recording reflects the neuronal activities from an extremely localized cortical region, it requires no complex analysis algorithms and, thus, is frequently employed in research including brain-machine interface (BMI) studies. However, the single-unit recording can be conducted only in an invasive way. To test if the NIRS technique has a potential to be utilized in noninvasive BMI studies, we carefully compared the results obtained by using the two techniques. The forepaws of rats were stimulated and the frequency of neuronal firing and the amplitude and slope of the oxy-hemoglobin increase were found to be proportional to the intensity of the peripheral stimulation. We believe that this result may provide some useful insights into the feasibility of using NIRS in noninvasive BMI studies.
    Journal- Korean Physical Society 06/2011; 58(6):1697-1702. · 0.51 Impact Factor
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    ABSTRACT: This study invesitigated the feasibility of measuring directional coupling between cortical areas with near-infrared spectroscopy (NIRS). Cerebral hemodynamic responses were recorded at the primary somatosensory cortex (S1), secondary somatosensory cortex (S2), and primary motor cortex (M1) regions of the rat barrel cortex during electrical stimulation of rat whiskers. Deoxyhemoglobin concentration changes were calculated from NIRS recordings and the Granger causality based on the multivariate autoregressive (MVAR) model was used to estimate the effective causal connectivity among S1, S2, and M1. The estimated causality patterns of seven rats showed consistent unidirectional coupling between the somatosensory areas and the motor areas (S1 and S2-->M1), which coincided well with our hypothesis because the rats' motor function was completely anesthetized. Our preliminary results suggest that cortico-cortical directional coupling can be successfully investigated with NIRS.
    Optics Express 03/2010; 18(6):5730-9. · 3.55 Impact Factor
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    ABSTRACT: We applied near-infrared spectroscopy (NIRS) and electroencephalography (EEG) simultaneously on the mouse brain and investigated the hemodynamic response to epileptic episodes under pharmacologically driven seizure. gamma-butyrolactone (GBL) and 4-aminopyridine (4-AP) were applied to induce absence and tonic-clonic seizures, respectively. The epileptic episodes were identified from the single-channel EEG, and the corresponding hemodynamic changes in different regions of the brain were characterized by multichannel frequency-domain NIRS. Our results are the following: (i) the oxyhemoglobin level increases in the case of GBL-treated mice but not 4-AP-treated mice compared to the predrug state; (ii) the dominant response to each absence seizure is a decrease in deoxyhemolobin; (iii) the phase shift between oxy- and deoxyhemoglobin reduces in GBL-treated mice but no 4-AP-treated mice; and (iv) the spatial correlation of hemodynamics increased significantly in 4-AP-treated mice but not in GBL-treated mice. Our results shows that spatiotemporal tracking of cerebral hemodynamics using NIRS can be successfully applied to the mouse brain in conjunction with electrophysiological recording, which will support the study of molecular, cellular, and network origin of neurovascular coupling in vivo.
    Journal of Biomedical Optics 01/2010; 15(3):037010. · 2.88 Impact Factor
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    ABSTRACT: We measured hemodynamic responses of seizure in the mouse brain using frequency-domain near infrared spectroscopy and electroencephalogram. Our results show that the cerebral oxygenation and hemodynamics in the mouse brain can be stably monitored.
    Biomedical Optics; 03/2008
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    ABSTRACT: Purpose Along with recent advances in neuroscience, near-infrared spectroscopy (NIRS) has been widely used to measure changes in cerebral oxygenation non-invasively. An NIRS system can be constructed to be portable unlike other imaging modalities, but its signals are often distorted by artifacts generated by arterial pulsation, vasomotion and head motion. To overcome these problems, we have developed a wireless NIRS system with a real time accelerometer that allows noise reduction. Methods Our wireless NIRS system includes a microcontroller, a Bluetooth communication, a fPCB (flexible printed circuit board), an accelerometer, batteries, LEDs (light emitting diode) and PDs (photodiode). Distorted signal caused by head motion was removed by active noise cancellation (ANC) algorithm. Results Two different tasks, arterial occlusion and brain hypoxia, were tested to validate the performance of our system. During arterial occlusion and breath holding, the NIRS signal showed corresponding hemodynamic changes such as increase in deoxy-hemoglobin (Hbr) and decrease in oxy-hemoglobin (HbO2) concentrations. Signal distortions generated by head motion were effectively removed. Conclusions Wireless NIRS system combined with real time noise cancellation algorithm has great potential to be utilized in brain-computer interface (BCI) for physically challenged people, dynamic exercise tasks and cognitive studies for children. Furthermore we expect the system will be highly applicable in neuroscience.
    Biomedical Engineering Letters. 1(4).