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Seung-Schik Yoo

Publications and source records attributed to Seung-Schik Yoo.

At least 19 recordsLinked to original sources
PubMed2005

Functional asymmetry in human primary auditory cortex: identified from longitudinal fMRI study.

The leftward hemispheric dominance in language processing may be associated with fundamental functional asymmetry in the primary auditory cortex (PAC). Based on repeated functional MRI (fMRI) measurements, we investigated the presence of functional asymmetry in the human PAC using binaural presentation of linguistic sounds (two-syllable nouns) and simple tonal stimulation. Eight right-handed volunteers underwent nine fMRI sessions, approximately eight weeks apart, spanning the duration of more than a year. The PAC from each hemisphere was manually segmented and the volume of activation, detected within the segmented region-of-interest, was measured across the subjects and sessions to generate functional laterality indices. Although variations existed in activation volume between sessions and subjects, we found predominant and consistent leftward functional asymmetry in PAC during both linguistic and non-linguistic sound stimulations.

Acoustic Stimulation↗
PubMed2005

The functional anatomy of sleep-dependent visual skill learning.

Learning of procedural skills develops gradually, with performance improving significantly with practice. But improvement on some tasks, including a visual texture discrimination task, continues in the absence of further practice, expressly during periods of sleep and not across equivalent waking episodes. Here we report that the brain activation revealed significantly different patterns of performance-related functional activity following a night of sleep relative to 1 h post-training without intervening sleep. When task activation patterns after a night of sleep were compared with activation patterns without intervening sleep (1 h post-training), significant regions of increased signal intensity were observed in the primary visual cortex, the occipital temporal junction, the medial temporal lobe and the inferior parietal lobe. In contrast, a region of decreased signal intensity was found in the right temporal pole. Corroborating these condition differences, correlations between behavioural performance and brain activation revealed significantly different patterns of performance-related functional activity following a night of sleep relative to those without intervening sleep. Together, these data provide evidence of overnight bi-directional changes in functional anatomy, differences that may form the neural basis of sleep-dependent learning expressed on this task.

Adult↗
PubMed2005

Head motion analysis during cognitive fMRI examination: application in patients with schizophrenia.

OBJECTIVES: Functional MRI (fMRI) has become an important imaging modality for analyzing the neural mechanisms underlying schizophrenia. Earlier studies indicate that patients with schizophrenia tend to generate involuntary and unnecessary head motion during visual tasks. Since head motion can deteriorate the quality of fMRI data, an investigation was needed to examine the type and extent of head motion from patients with schizophrenia undergoing fMRI. METHODS: Patients with schizophrenia and demographically-matched healthy comparison subjects underwent fMRI examination involving visual working memory tasks. We obtained head movement parameters (three translational and three rotational) through mathematical realignment of the volumetric image data, and transformed these parameters into head displacement indices to quantify the subject's head motion in space. RESULTS: We found no group difference in displacement indices between the two groups. Group comparison of movement parameters indicated that the patient group showed reduced head motion along the superior-inferior direction when compared to healthy individuals. CONCLUSION: These results suggest that cognitive fMRI examination in patients with schizophrenia can be successfully conducted without the deteriorative effects of head motion.

Adult↗
PubMed2005

Long-term reproducibility analysis of fMRI using hand motor task.

This article reports test-retest reproducibility of functional MRI (fMRI) measurement on brain activation elicited by auditory-cued sequential finger tapping. Eight right-handed volunteers participated in nine fMRI sessions, approximately eight weeks apart, for the duration of more than a year. The first scan session was repeated within a day to examine the intra-session reproducibility. The frequency of activation for neural substrates relevant to the task was constructed across the subjects and sessions. The spatial reproducibility was measured as the ratio of the size of the volume as well as its overlaps with respect to the first scan session from regions-of-interest in the selected motor circuitry. Consistent activation patterns between sessions and across subjects were observed in the sensorimotor areas such as the left primary, supplementary, and premotor areas, as well as in the right cerebellar areas without evidence of session-dependent trends. Quantitative analysis showed that the reproducibility measures varied within the range obtained from studies on fMRI reproducibility covering much shorter terms. Intra-session fMRI scans yielded slightly better reproducibility measures compared to the results obtained from other scan sessions. The findings suggest that the reproducible fMRI measurement can be obtained for long-term monitoring of brain function.

Acoustic Stimulation↗
PubMed2005

Working memory processing of facial images in schizophrenia: fMRI investigation.

Impaired processing of facial information is one of the broad ranges of cognitive deficits seen in patients with schizophrenia. This study aimed to elucidate the differences in brain activities involved in the process of facial working memory (images of neutral faces as mnemonic content) between schizophrenic patients and healthy comparison subjects using functional magnetic resonance imaging (fMRI). Group comparison analysis revealed aberrant activities from the patient group in several cortical areas, including the left fusiform gyrus, right superior frontal gyrus, bilateral middle frontal gyri/insula, and left middle temporal gyrus. A decreased level of activity in the left fusiform gyrus, along with performance reduction, implicates abnormal processing of facial information in schizophrenia.

Adult↗
PubMed2005

In vivo visualization of white matter fiber tracts of preterm- and term-infant brains with diffusion tensor magnetic resonance imaging.

OBJECTIVE: The goal of this study was to test the feasibility of visualizing a 3-dimensional structure of cerebral white matter fiber tracts in preterm infants, postconceptional age (PCA) 28 weeks to term, by using volumetric diffusion tensor magnetic resonance imaging (DTI) data. MATERIALS AND METHOD: We combined tractography algorithms and visualization methods, currently available for adult DTI data, to trace the pixelated principal direction of a diffusion tensor originating from regions-of-interest with high fractional anisotropy. Consequently, white matter fiber bundles from the genu and the splenium of corpus callosum, the corticospinal tracts, the inferior fronto-occipital fasciculi, and optic radiations were visualized. RESULTS: Our results suggest that major white matter tracts of preterm infant brains, with PCAs ranging from 28 weeks to term (40 weeks old), can be successfully visualized despite the small brain volume and low anisotropy. CONCLUSION: The feasibility of fiber tractography in preterm neonates with DTI may add a new dimension in detection and characterization of white matter injuries of preterm infants.

Algorithms↗
PubMed2004

Brain-computer interface using fMRI: spatial navigation by thoughts.

A brain-computer interface (BCI) is a way of conveying an individual's thoughts to control computer or electromechanical hardware. Capitalizing on the ability to characterize brain activity in a reproducible manner, we explored the possibility of using real-time fMRI to interpret the spatial distribution of brain function as BCI commands. Using a high-field (3T) MRI scanner, brain activities associated with four distinct covert functional tasks were detected and subsequently translated into predetermined computer commands for moving four directional cursors. The proposed fMRI-BCI method allowed volunteer subjects to navigate through a simple 2D maze solely through their thought processes.

Adult↗
PubMed2004

Evaluating requirements for spatial resolution of fMRI for neurosurgical planning.

The unambiguous localization of eloquent functional areas is necessary to decrease the neurological morbidity of neurosurgical procedures. We explored the minimum spatial resolution requirements for functional magnetic resonance imaging (fMRI) data acquisition when brain mapping is used in neurosurgical planning and navigation. Using a 1.5 Tesla clinical MRI scanner, eight patients with brain tumors underwent fMRI scans using spatial resolution of approximately 4 x 4 x 4 mm(3) to map the eloquent motor and language areas during the performance of cognitive/sensorimotor tasks. The fMRI results were then used intra-operatively in an open MRI system to delineate eloquent areas. Retrospectively, activation patterns were visually inspected by a neurosurgeon to determine qualitatively whether ambiguity with respect to the activation boundaries, due to low spatial resolution, could be of potential significance for surgical guidance. A significant degree of ambiguity in both the extent and shape of activation was judged to be present in data from six of the eight patients. Analysis of fMRI data at multiple resolutions from a normal volunteer showed that at 3 mm isotropic resolution, eloquent areas were better localized within the gray matter although there was still some potential for ambiguity caused by activations appearing to cross a sulcus. The data acquired with 2-mm isotropic voxels significantly enhanced the spatial localization of activation to within the gray matter. Thus, isotropic spatial resolution on the order of 2 x 2 x 2 mm(3), which is much higher than the resolutions used in typical fMRI examinations, may be needed for the unambiguous identification of cortical activation with respect to tumors and important anatomical landmarks.

Adult↗
PubMed2004

Functional MRI of auditory verbal working memory: long-term reproducibility analysis.

Although functional MRI (fMRI) has shown to be a tool with great potential to study the normal and diseased human brain, the large variability in the detected hemodynamic responses across sessions and across subjects hinders a wider application. To investigate the long-term reproducibility of fMRI activation of verbal working memory (WM), eight normal subjects performed an auditory version of the 2-back verbal WM task while fMRI images were acquired. The experiment was repeated nine times with the same settings for image acquisition and fMRI task. Data were analyzed using SPM99 program. Single-session activation maps and multi-subject session-specific activation maps were generated. Regions of interest (ROIs) associated to specific components of verbal WM were defined based on the voxels' coordinates in Talairach space. Visual observation of the multi-subject activation maps showed similar activation patterns, and quantitative analysis showed small coefficients of variance of activation within ROIs over time, suggesting small longitudinal variability of activation. Visual observation of the activation maps of individual sessions demonstrated striking variation of activation across sessions and across subjects, and quantitative analysis demonstrated larger contribution from between-subject variation to overall variation than that from within-subject variation. We concluded that by multi-subject analysis of data from a relatively small number of subjects, reasonably reproducible activation for the 2-back verbal WM paradigm can be achieved. The level of reproducibility encourages the application of this fMRI paradigm to the evaluation of cognitive changes in future investigations. The quantitative estimation of the proportions of within-subject and between-subject variabilities in the overall variability may be helpful for the design of future studies.

Acoustic Stimulation↗
PubMed2004

Modulation of cerebellar activities by acupuncture stimulation: evidence from fMRI study.

Recent neuroimaging studies have revealed that acupuncture stimulation modulates human central nervous system including cerebral limbic/paralimbic and subcortical structures. Due to the wide and intricate connections with cerebrum, we hypothesized that anatomically specific areas in human cerebellum are also modulated by acupuncture stimulation beyond classical involvement of cerebellum in motor coordination. Functional MRI (fMRI) was used to investigate neural substrates responding to the acupuncture stimulation of Pericardium 6 (PC6, Neiguan), an acupoint relevant for the management of nausea including vestibular-related motion sickness. Sham stimulation near the acupoint and tactile stimulation on the skin of the acupoint were given as separate conditions. Psychophysical scores as well as the heart and respiratory rates were measured during each condition. Acupuncture manipulation on PC6, in comparison to the sham acupuncture and tactile stimulation conditions, selectively activated left superior frontal gyrus, anterior cingulate gyrus, and dorsomedial nucleus of thalamus. Acupuncture-specific neural substrates in cerebellum were also evident in declive, nodulus, and uvula of vermis, quadrangular lobule, cerebellar tonsil, and superior semilunar lobule. Negative MR signal changes, often seen during the acupuncture of analgesic points, were not observed in the present study. Our data suggest that cerebellum serves as important activation loci during the acupuncture stimulation of PC6, and clinical efficacy of PC6 may be mediated by the cerebellar vestibular neuromatrix.

Acupuncture↗
PubMed2004

Neural substrates associated with the concurrent performance of dual working memory tasks.

The neural substrates of the dual working memory (WM) process were investigated using concurrent performance of auditory and visual n-back WM tasks. Based on the pre-fMRI behavioral testing, a lettered 1-back WM paradigm was implemented for an fMRI examination of healthy volunteers who performed (1) auditory, (2) visual, and (3) simultaneous visual and auditory WM tasks. The behavioral performance, as measured by the reaction time, was deteriorated in the dual task condition compared to the single task condition. Group analysis of the fMRI data revealed that the majority of activation identified during each component task was concurrently activated in the dual task condition. However, several neural substrates such as left middle frontal gyrus, left superior parietal lobule, posterior aspect of right inferior temporal gyrus, and bilateral parahippocampal gyri were selectively activated during the dual WM task. These data suggest that new neural networks come into play to assist in the greater load placed on the WM with the incongruent stimulation modality, which may also have implications in crossmodal integrative processes.

Acoustic Stimulation↗
PubMed2004

Neuronal dysfunction of the frontal lobe in schizophrenia.

Localized in vivo proton magnetic resonance spectroscopy (MRS) was performed to evaluate metabolic alterations in the right and left frontal lobe before and after antipsychotic treatment of schizophrenic patients (n=24) and a group of healthy normal subjects (n=20). Proton metabolic ratios obtained from the 8 cm3 voxels in the right and left frontal lobes were compared with the clinical assessment for each subject. There was no significant difference in the metabolic ratios between the right and the left frontal lobes in either the schizophrenic group or the control group, indicating no laterality. Compared with those of the normal control group, NAA/Cr ratio of the schizophrenic patients showed significantly lower value. The NAA/Cr ratio of the schizophrenic patients was not changed after antipsychotic treatment. The present study supports the 'hypofrontality' hypothesis of schizophrenia.

Adolescent↗
PubMed2003

Neural substrates of tactile imagery: a functional MRI study.

fMRI investigation on the neural substrates involved in tactile imagery is reported. Healthy subjects performed mental imagery of tactile stimulation on the dorsal aspect of the right hand. The results were compared with the regions of activation during the actual tactile stimulation. During imagery, contralateral primary and secondary somatosensory areas were activated along with activation in the left parietal lobe. Activations in left inferior frontal gyri (Brodmann's area 44), left dorsolateral prefrontal area, left precentral gyrus, left insula, and medial frontal gyrus were also observed. In the basal ganglia, activation in the left thalamus (ventral posteromedial nucleus) and putamen was found. Our results suggest that the primary and secondary somatosensory areas are recruited during tactile imagery, and have partially overlapping neural substrates for the perception of tactile stimulation.

Adult↗
PubMed2003

Tourniquet application to facilitate axillary venous access in percutaneous central venous catheterization.

The authors evaluated the location of peripheral venous lines and changes in opacification of cephalic and axillary veins at fluoroscopically guided venography after tourniquet application. Results suggested that tourniquet application effectively reduces the superficial venous flow and consequently enhances the opacification of the axillary veins. Tourniquet application is a simple and effective way of facilitating axillary venous puncture.

Angiography, Digital Subtraction↗
PubMed2003

Selection of voxel size and slice orientation for fMRI in the presence of susceptibility field gradients: application to imaging of the amygdala.

The impact of voxel geometry on the blood oxygenation level-dependent (BOLD) signal detectability in the presence of field inhomogeneity is assessed and a quantitative approach to selecting appropriate voxel geometry is developed in this report. Application of the developed technique to BOLD sensitivity improvement of the human amygdala is presented. Field inhomogeneity was measured experimentally at 1.5 T and 3 T and the dominant susceptibility field gradient in the human amygdala was observed approximately along the superior-inferior direction. Based on the field mapping studies, an optimal selection for the slice orientation would be an oblique pseudo-coronal plane with its frequency-encoding direction parallel to the field gradient measured from each subject. Experimentally this was confirmed by comparing the normalized standard deviation of time-series echo-planar imaging signals acquired with different slice orientations, in the absence of a functional stimulus. A further confirmation with a carefully designed functional magnetic resonance imaging study is needed. Although the BOLD sensitivity may generally be improved by a voxel size commensurable with the activation volume, our quantitative analysis shows that the optimal voxel size also depends on the susceptibility field gradient and is usually smaller than the activation volume. The predicted phenomenon is confirmed with a hybrid simulation, in which the functional activation was mathematically added to the experimentally acquired rest-period echo-planar imaging data.

Adult↗
PubMed2003

Added benefit of thoracic aortography after transarterial embolization in patients with hemoptysis.

OBJECTIVE: The purpose of this study was to examine the usefulness of thoracic aortography performed after transarterial embolization in identifying additional arteries responsible for causing hemoptysis. SUBJECTS AND METHODS: Between March 2000 and November 2001, we prospectively performed thoracic aortography after transarterial embolization in 76 patients with hemoptysis. Underlying diseases included tuberculosis (n = 34), bronchiectasis (n = 30), emphysema (n = 4), bronchitis (n = 4), aspergillosis (n = 3), and lung cancer (n = 1). Initially, angiography of bronchial and other systemic arteries possibly contributing to hemoptysis was performed with embolization. After completion of the embolization, thoracic aortography was performed, with the tip of the catheter located just distal to the origin of the left subclavian artery. RESULTS: A total of 200 arteries (52 right bronchial, 40 left bronchial, six common bronchial, 76 intercostal, 11 inferior phrenic, six thoracodorsal, eight internal mammary, and one thyrocervical) were identified either at the initial embolization or on thoracic aortography as being responsible for causing hemoptysis. Among them, 29 arteries (14.5%) that were not included on the initial selection for embolization were later identified on postembolization thoracic aortography. There were two right bronchial, three left bronchial, eight inferior phrenic, and 16 intercostal arteries. CONCLUSION: The inferior phrenic and intercostal arteries were often missed on routine transarterial embolization in patients with hemoptysis. Postembolization thoracic aortography is useful for monitoring the effectiveness of embolization and for improving the detection of arteries contributing to hemoptysis.

Adult↗