Biomedical subjects

Tak Youn

Publications and source records attributed to Tak Youn.

17 recordsLinked to original sources

PubMed2005

Functional imaging evidence of the relationship between recurrent psychotic episodes and neurodegenerative course in schizophrenia.

It remains controversial as to what determines the neurodegenerative course in schizophrenia. This study administered a modified version of the Stroop task and investigated the relationship between functional magnetic resonance imaging (fMRI) signal changes in dysfunctioned task-related regions and clinical course variables. Functional MRI data during task performance were acquired from 10 right-handed schizophrenic patients (mean+/-SD age=29.2+/-10.3 years, range of illness duration=0.8-14 years, number of episodes=1-5) and 10 healthy controls (mean+/-SD age=30.3+/-6.4). Imaging data were investigated on a voxel-by-voxel basis for single group analysis and for between-group analysis according to the random effect model using Statistical Parametric Mapping (SPM 99b). Correlation analysis with age as a covariate identified those brain regions whose fMRI signal changes were significantly related to clinical course variables in schizophrenia. The number of psychotic episodes was negatively correlated with the fMRI signal change in the right inferior frontal and the right frontal precentral gyri among the activated regions during the Stroop task in schizophrenia, whereas the length of illness was not so correlated. The number of psychotic episodes was also negatively correlated with the fMRI signal change in the left paracingulate in which functional activity was diminished in the patients relative to the controls. Our results indicate that recurrent psychotic episodes are related to the neurodegenerative course in some dysfunctional brain regions in schizophrenia.

Adolescent↗

PubMed2005

Decreased caudal anterior cingulate gyrus volume and positive symptoms in schizophrenia.

The anterior cingulate gyrus is a heterogeneous region that has specialized subdivisions with respect to its cytoarchitecture, function and connectivity. The aim of this study was to examine the morphological changes of the caudal subdivision of the anterior cingulate gyrus in the context of the cortico-striatal-thalamo-cortical circuitry of schizophrenia and their relationship to clinical symptoms. Accordingly, we measured the volumes of the caudal and rostral anterior cingulate gyrus, the orbitofrontal cortex, the caudate and the thalamus by magnetic resonance imaging in age- and sex-matched groups, which consisted of 22 patients with schizophrenia and 22 normal volunteers. The clinical symptoms of schizophrenia patients were obtained using the Positive and Negative Syndrome Scale. Volumetric reduction of the right caudal anterior cingulate gyrus was observed in patients with schizophrenia as compared with the normal controls. Furthermore, a smaller volume of the caudal anterior cingulate gyrus was significantly correlated with more severe positive symptoms of schizophrenia. Thus, these findings suggest that a volumetric abnormality of the caudal anterior cingulate gyrus in schizophrenia may be related to positive symptoms and possibly involved in the pathophysiology of schizophrenia.

Adult↗

PubMed2004

Gray matter abnormalities in paranoid schizophrenia and their clinical correlations.

Numerous imaging studies have shown structural brain abnormalities in schizophrenia. Recently, voxel-based morphometry enabled whole brain analysis beyond the regions of interest (ROI). Regional gray matter concentrations of magnetic resonance (MR) images from 35 patients with paranoid schizophrenia were compared with those from 35 age- and sex-matched controls, and their clinical correlations were explored using voxel-based morphometry. Gray matter concentrations in the patients were significantly reduced in the left insular and dorsolateral prefrontal regions, and bilaterally in the medial frontal, anterior cingulate, inferior frontal and superior temporal regions. On the other hand, gray matter concentrations in the bilateral cerebellum and right striatum were significantly increased in the patients compared with controls. A negative correlation between the score for the severity of 'lack of insight and judgment' and gray matter concentrations in the left posterior and right anterior cingulate and bilateral inferior temporal regions including the lateral fusiform gyri was found. These results suggest the important roles of the paralimbic structures in the pathophysiology of schizophrenia and the involvement of the perceptual and monitoring systems in the mechanism of insight.

Adult↗

PubMed2004

Impairment of recognition memory in schizophrenia: event-related potential study using a continuous recognition task.

Recognition memory and the dissociation of immediate and delayed repetition in schizophrenic patients were investigated using event-related potential (ERP) and a continuous word recognition task. In total, 14 schizophrenic patients and 14 age and gender-matched control subjects, were recruited. Among 240 stimulus words used, 40 words were not repeated, 100 were repeated immediately, and 100 were repeated after five intervening words. Both schizophrenic and control groups responded faster to words repeated immediately than to words repeated after a delay and to new words. However, schizophrenic patients responded less accurately to words repeated immediately and to words repeated after a delay than the controls. In terms of ERP, schizophrenic patients showed significantly reduced N200, late positive component (LPC), and N400 amplitudes, and a more frontally-distributed N200 topography than the controls. For controls, immediate repetition was associated with a large LPC amplitude and the absence of N400, while delayed repetition was associated with a small LPC amplitude and the presence of N400. However, this dissociation between immediate and delayed repetition was not observed in schizophrenic patients. All of these results suggest that schizophrenic patients have recognition memory impairment, the cause of which may range from early encoding, and memory search to late retrieval.

Adult↗

PubMed2004

Volumetric investigation of the frontal-subcortical circuitry in patients with obsessive-compulsive disorder.

The pathophysiology of obsessive-compulsive disorder (OCD) is thought to involve disturbance of the frontal-subcortical circuitry. To investigate the morphological characteristics of this circuitry, we examined the volume of the orbitofrontal cortex, anterior cingulate, thalamus, caudate, and the putamen in 36 age- and sex-matched OCD patients and normal control subjects using three-dimensional magnetic resonance (MR) brain imaging. The left orbitofrontal volumes were found to be significantly smaller in the OCD patients and showed significant negative correlations with obsessive-compulsive symptom severity. These findings suggest that a structural abnormality of this brain region is implicated in the pathophysiology of OCD.

Adult↗

PubMed2003

Neuropsychological correlates of P300 abnormalities in patients with schizophrenia and obsessive-compulsive disorder.

The cognitive significance of P300 abnormalities in schizophrenia and obsessive-compulsive disorder (OCD) was investigated. P300 was measured by an auditory oddball paradigm, in which a series of standard tones (1000 Hz) and target tones (1500 Hz) were presented. The subject's task was to count the number of the presented target tones. Cognitive functions were evaluated by neuropsychological tests, which were chosen to be sensitive to frontal and temporal dysfunction. Twenty-two schizophrenic patients, 19 OCD patients and 21 healthy controls participated. Event-related potentials measured at 15 electrode sites, which consisted of five levels on the left-right dimension and three levels on the anterior-posterior dimension, were included in the statistical analysis. P300 amplitudes on all 15 electrode sites were significantly smaller in schizophrenic and OCD patients than in the controls. Schizophrenic patients performed poorly on almost all neuropsychological tests, while OCD patients showed impaired performance on the Rey-Osterrieth Complex Figure Test and on a controlled oral word association test. In schizophrenic patients, P300 amplitude was associated with performance on verbal memory and learning by the Luria-Nebraska Neuropsychological Battery, while for OCD patients, P300 amplitude was related to the Trail Making Test, Part B response time. These results indicate that schizophrenic patients have generalized cognitive impairments, which are substrated by a wide range of cortical dysfunctions. The major cognitive deficits observed in OCD patients were impairments of controlled attention and self-guided, flexible behavior, which are mediated by the fronto-striatal system. The neurophysiological mechanisms underlying P300 abnormalities observed in schizophrenic and OCD patients are discussed.

Acoustic Stimulation↗

PubMed2003

Morphometric abnormality of the insula in schizophrenia: a comparison with obsessive-compulsive disorder and normal control using MRI.

The insula is increasingly the subject of great interest in psychiatric disorders of neurodevelopmental origin because of its anatomical location, wide interconnectivity, and variety of functions. This study explores the possible morphometric change of the insula in schizophrenia and obsessive-compulsive disorder (OCD), and its potential relationship to clinical symptoms. The insula was traced on all coronal slices of magnetic resonance images of three age- and sex-matched diagnostic groups, which consisted of 21 patients with schizophrenia, 21 patients with OCD and 21 normal volunteers. The volumetric measures of the insula were compared among the three groups, and their relationships to the symptom severity were investigated. Volumetric reduction of the left insula was observed in the schizophrenia group, but not in the OCD group. These results confirm the involvement of deficient insular function in the pathophysiology of schizophrenia.

Adult↗

PubMed2003

Altered hemispheric asymmetry and positive symptoms in schizophrenia: equivalent current dipole of auditory mismatch negativity.

The abnormality of mismatch negativity (MMN) in schizophrenia is thought to be associated with perceptional disturbance and cognitive dysfunction. The purpose of the present study was to investigate the change of the normal functional hemispheric lateralization in schizophrenia by employing the equivalent current dipole (ECD) model of auditory MMN with individual MRI and high-density electroencephalography (EEG). The MMNs resulting from auditory stimuli with passive oddball paradigm in a group of schizophrenics (n = 15), and also a group of age-, sex-, and handedness-matched normal controls, were recorded by 128 channel EEG. The location and power of ECD sources at the peak point were calculated. Individual 3-D brain magnetic resonance images (MRI) were used for realistic head modeling and for source localization. For both groups, the MMN source was determined to be located in the superior temporal gyrus (STG). However, the normal functional hemispheric asymmetry of ECD power was significantly altered in the schizophrenics (chi(2) test = 16.13, p < 0.001). Left MMN ECD power and the asymmetry coefficient (AC) were negatively correlated with the positive scores from Positive and Negative Syndrome Scale (PANSS) (r = -0.673, p = 0.008), especially with the hallucinatory behavior subscale (r = -0.677, p = 0.008). These findings support the deficits in preattentive automatic processing of auditory stimuli, especially in the left hemisphere, and indicate the correlation between positive symptoms, especially auditory hallucination, and left temporal lobe dysfunction in schizophrenia.

Adult↗

PubMed2003

Independent component model for cognitive functions of multiple subjects using [15O]H2O PET images.

An independent component model of multiple subjects' positron emission tomography (PET) images is proposed to explore the overall functional components involved in a task and to explain subject specific variations of metabolic activities under altered experimental conditions utilizing the Independent component analysis (ICA) concept. As PET images represent time-compressed activities of several cognitive components, we derived a mathematical model to decompose functional components from cross-sectional images based on two fundamental hypotheses: (1) all subjects share basic functional components that are common to subjects and spatially independent of each other in relation to the given experimental task, and (2) all subjects share common functional components throughout tasks which are also spatially independent. The variations of hemodynamic activities according to subjects or tasks can be explained by the variations in the usage weight of the functional components. We investigated the plausibility of the model using serial cognitive experiments of simple object perception, object recognition, two-back working memory, and divided attention of a syntactic process. We found that the independent component model satisfactorily explained the functional components involved in the task and discuss here the application of ICA in multiple subjects' PET images to explore the functional association of brain activations.

Adult↗

PubMed2003

LORETA imaging of P300 in schizophrenia with individual MRI and 128-channel EEG.

We investigated the characteristics of P300 generators in schizophrenics by using voxel-based statistical parametric mapping of current density images. P300 generators, produced by a rare target tone of 1500 Hz (15%) under a frequent nontarget tone of 1000 Hz (85%), were measured in 20 right-handed schizophrenics and 21 controls. Low-resolution electromagnetic tomography (LORETA), using a realistic head model of the boundary element method based on individual MRI, was applied to the 128-channel EEG. Three-dimensional current density images were reconstructed from the LORETA intensity maps that covered the whole cortical gray matter. Spatial normalization and intensity normalization of the smoothed current density images were used to reduce anatomical variance and subject-specific global activity and statistical parametric mapping (SPM) was applied for the statistical analysis. We found that the sources of P300 were consistently localized at the left superior parietal area in normal subjects, while those of schizophrenics were diversely distributed. Upon statistical comparison, schizophrenics, with globally reduced current densities, showed a significant P300 current density reduction in the left medial temporal area and in the left inferior parietal area, while both left prefrontal and right orbitofrontal areas were relatively activated. The left parietotemporal area was found to correlate negatively with Positive and Negative Syndrome Scale total scores of schizophrenic patients. In conclusion, the reduced and increased areas of current density in schizophrenic patients suggest that the medial temporal and frontal areas contribute to the pathophysiology of schizophrenia, the frontotemporal circuitry abnormality.

Adolescent↗

PubMed2003

N-methyl-D-aspartate receptor in working memory impairments in schizophrenia: event-related potential study of late stage of working memory process.

Working memory (WM) deficit in schizophrenic patients has been well established. Still, underlying biological substrate of the impairment is not clear. Among neurotransmitter hypotheses of schizophrenia, N-methyl-D-aspartate (NMDA) receptor model is mostly supported, considering that NMDA receptor antagonist can elicit both psychosis and cognitive impairment observed in schizophrenic patients. In current study, to test the neuropsychological and the electrophysiological effects of NMDA receptor in WM, event-related potentials (ERPs) of Sternberg's short-term memory scanning task (SMST) were analyzed in 10 healthy subjects under intravenous administration of a subanesthetic dose of ketamine (0.65 mg/kg/h) or placebo (normal saline). Late positive component (LPC) of ERP was hypothesized to reflect later stage of WM. Brief Psychiatric Rating Scale score was significantly increased (t=-5.75, df=9, P<.001) and correct response rate was significantly decreased (t=2.21, df=9, P=.054) after ketamine administration. Neither reaction time nor LPC latency, which reflect memory scanning time, was changed. Amplitude of LPC was significantly reduced after ketamine administration (z=-2.31, number of observations=120, P=.021). In conclusion, NMDA receptor antagonist administration elicited WM deficit both in behavioral and electrophysiological level. Electrophysiological component reflecting later stage of WM was impaired by NMDA antagonist.

Adult↗

PubMed2003

Optimized individual mismatch negativity source localization using a realistic head model and the Talairach coordinate system.

The purpose of this study is to evaluate the difference between anatomical locations of mismatch negativity (MMN) generators using a realistic head model and the Talairach coordinate system. This was performed by dipole source analysis by using a high density 128 channel electroencephalography (EEG) acquisition system and the subjects' individual 3D magnetic resonance images (MRI) for the realistic head model, in 24 healthy subjects. For dipole source localization, both the Talairach coordinate system and the individual MRI realistic head models were used and location results were compared. The MMN generators were clearly localized in the superior temporal gyri, especially in Heschl's gyrus, according to each individual's structural MRI. Only 37.5% of subjects showed the same anatomical locations of the MMN generator in both hemispheres in the realistic head model and in Talairach coordinate system, but fifteen subjects (62.5%) didn't. This result indicates that individually registered functional locations are desirable for the precise localization of activated areas in functional imaging studies and that a brain coordinate system is needed which adequately accounts for ethnic differences.

Acoustic Stimulation↗

PubMed2003

Classification of frequency distributions of diagnostic criteria scores in twelve personality disorders by the curve fitting method.

The purpose of the present study was to investigate whether each personality disorder (PD) has a different frequency distribution of diagnostic criteria, and to classify the distribution of each PD on the basis of shape by the curve fitting method. A total of 4740 male subjects in early adulthood completed the Korean version of the Personality Diagnostic Questionnaire (4th revision; PDQ-4+). The frequency distribution of scores in each PD was specified to the best fitted model by the curve estimation procedure. Twelve distributions of PD criteria were fitted to three types of curve models (quadratic, cubic, and logistic). The quadratic model included obsessive-compulsive and histrionic PD. The cubic model included borderline, narcissistic, avoidant, passive-aggressive, paranoid, and schizotypal PD. The logistic model contained dependent, depressive, schizoid, and antisocial PD. The results suggest that each PD has a different type of distribution and each distribution of PD might be classified to a specific curve model. Also, the results suggest that the issue of continuities between PD and the normal group could not be generalized to all PD, but should be considered individually for each PD.

Adult↗

PubMed2003

Functional disconnection between the prefrontal and parietal cortices during working memory processing in schizophrenia: a[15(O)]H2O PET study.

OBJECTIVE: The prefrontal-parietal circuits have been reported to play an important role in working memory. The purpose of this study was to use direct neuroimaging to address whether interregional correlation in the prefrontal-parietal circuits is impaired in schizophrenia. METHOD: [(15)O]H(2)O positron emission tomography was used to compare regional blood flow changes in 12 schizophrenic and 12 healthy comparison subjects during the n-back sequential-picture working memory task. Interregional correlation was assessed by correlating the regional activation of the lateral prefrontal area with that of other activated areas in each subject group. RESULTS: Dorsolateral prefrontal activation was observed around the right superior frontal sulcus in the healthy subjects, and ventrolateral prefrontal activation below the right inferior frontal sulcus was observed in the schizophrenic patients. Activation in the right lateral prefrontal cortex was significantly correlated with activation in the bilateral inferior parietal region in the healthy subjects but was not correlated with any regional activation in the patients. CONCLUSIONS: The findings suggest prefrontal-parietal functional disconnection, particularly prefrontal dissociation and abnormal prefrontal-parietal interaction, during working memory processing in schizophrenia.

Adult↗

PubMed2002

Statistical parametric mapping of LORETA using high density EEG and individual MRI: application to mismatch negativities in schizophrenia.

We describe a method for the statistical parametric mapping of low resolution electromagnetic tomography (LORETA) using high-density electroencephalography (EEG) and individual magnetic resonance images (MRI) to investigate the characteristics of the mismatch negativity (MMN) generators in schizophrenia. LORETA, using a realistic head model of the boundary element method derived from the individual anatomy, estimated the current density maps from the scalp topography of the 128-channel EEG. From the current density maps that covered the whole cortical gray matter (up to 20,000 points), volumetric current density images were reconstructed. Intensity normalization of the smoothed current density images was used to reduce the confounding effect of subject specific global activity. After transforming each image into a standard stereotaxic space, we carried out statistical parametric mapping of the normalized current density images. We applied this method to the source localization of MMN in schizophrenia. The MMN generators, produced by a deviant tone of 1,200 Hz (5% of 1,600 trials) under the standard tone of 1,000 Hz, 80 dB binaural stimuli with 300 msec of inter-stimulus interval, were measured in 14 right-handed schizophrenic subjects and 14 age-, gender-, and handedness-matched controls. We found that the schizophrenic group exhibited significant current density reductions of MMN in the left superior temporal gyrus and the left inferior parietal gyrus (P < 0. 0005). This study is the first voxel-by-voxel statistical mapping of current density using individual MRI and high-density EEG.

Adolescent↗

PubMed2002

Relationship between personality trait and regional cerebral glucose metabolism assessed with positron emission tomography.

There have been no studies systematically investigating relationships between biogenetic temperament dimensions and patterns of brain glucose metabolism. Nineteen healthy subjects were evaluated regarding the biogenetic temperament using Cloninger's Temperament and Character Inventory (TCI). In addition, [18F] fluorodeoxyglucose (FDG) positron emission tomography (PET) was used to measure regional brain glucose metabolism. Voxel-based correlation analysis was used to test correlations between regional brain glucose metabolism and scores on the TCI. We identified that each temperament dimension, such as Novelty Seeking, Harm Avoidance, and Reward Dependence, was significantly correlated with specific brain regions. The majority of correlations were observed in the areas of paralimbic regions and temporal lobes. The current study provides evidence linking each biogenetic temperament dimension with specific brain areas and provides a promising base for future personality research.

Adolescent↗

PubMedDate not supplied

Left anterior subregion of orbitofrontal cortex volume reduction and impaired organizational strategies in obsessive-compulsive disorder.

The orbitofrontal cortex (OFC) may be involved in the clinical and cognitive expressions of obsessive-compulsive disorder (OCD) and is a heterogenous region with respect to its cytoarchitecture, function and connectivity. This study was designed to examine the morphological abnormality of the anterior subregion of OFC and its relationship to clinical symptoms and cognitive performance in patients with OCD. We divided the OFC into anterior and posterior subregions using an external landmark and measured the gray matter volumes of each by three-dimensional magnetic resonance imaging in age- and sex-matched groups, which consisted of 34 OCD and 34 normal volunteers. Clinical and cognitive evaluations were completed using Yale-Brown Obsessive Compulsive Scale (YBOCS) and four sets of neuropsychological tests that assessed executive functions and visual memory. Volume reduction of the left anterior OFC was observed in patients with OCD versus normal controls. Also, a significant positive correlation was found between left anterior OFC gray matter volume and the copy score of the Rey-Osterrieth Complex Figure Test in patients with OCD. These results suggest that left anterior subregion volume reduction of the OFC may be related to impaired organizational strategies in patients with OCD.

Adult↗