1,720,985 research outputs found
Spatiotemporal brain activation pattern during word/picture perception by native Koreans
No full textThe purpose of this study is to explore spatiotemporal brain activation patterns during perception of words from three different languages (Korean, English, Chinese) and pictures. Using 64 channel event-related potential (ERP) recording and source localization using distributed source model, we investigated, with high temporal resolution, whether similar or different spatiotemporal patterns of brain activation are involved in the perception of words of different languages and/or pictures. Experimental results seem to corroborate left hemispheric dominance in language processing, and temporal/spatial characteristics in word perception revealed by previous ERP and neuroimaging studies. Observed differences in spatial pattern of activation at specific time periods between English and Korean, and Korean and Chinese, could be explained in terms of required visual pattern analysis due to the orthographic characteristics of each language
Improved ballistocardiac artifact removal from the electroencephalogram recorded in fMRI
No full textThe simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance image (fMRI) is a promising tool that is capable of providing hi.-h spatiotemporal brain mapping, with each modality supplying complementary information. One of the major barriers to obtain high-quality simultaneous EEG/fMR1 data is that pulsatile activity due to the heartbeat induces significant artifacts in the EEG. The purpose of this study was to develop a novel algorithm for removing heartbeat artifact, thus overcoming problems associated with previous methods. Our method consists of a mean artifact wave form subtraction, the selective removal of wavelet coefficients, and a recursive least-square adaptive filtering. The recursive least-square adaptive filtering operates without dedicated sensor for the reference signal, and only when the mean subtraction and wavelet-based noise removal is not satisfactory. The performance of our system has been assessed using simulated data based on experimental data of various spectral characteristics, and actual experimental data of alpha-wave-dominant normal EEG and epileptic EEG. (C) 2004 Elsevier B.V. All rights reserved
Brain activation of reading Korean words and recognizing pictures by korean native speakers: A functional magnetic resonance imaging study
No full textEven though the Korean words are characterized as phonemes like other alphabetic languages, their shape resembles much more morphemes like Chinese characters. The main purpose of the study is to explore neural mechanisms of reading Korean words and recognizing pictures by Korean native speakers using functional magnetic resonance imaging technique. In the experimental results, the authors Could see commonly activated areas in occipito-temporal region bilaterally, whereas frontal and temporal region was activated only while reading Korean words. Left middle frontal activation of Korean words was regarded to be involved in the phonological and semantic processing. Right anterior cingulate (BA 32) activation seems to be related with language and sound organization and superior temporal (BA 29) activation might be involved in the processing of phonological system to which tonal information is attached. Right medial frontal (BA 8) activation was reported in the results. The authors suggest the activation of this area is related with nonverbal visual higher order control or visuospatial analysis of Korean words in their experimental tasks
Neural mechanisms of Korean word reading: a functional magnetic resonance imaging study
Full text linkThe use of functional magnetic resonance imaging permits the collection of brain activation patterns when native Korean speakers (12 persons as subjects) read Korean words and Chinese characters. The Korean language uses both alphabetic Korean words and logographic Chinese characters in its writing system. Our experimental results show that the activation patterns obtained for reading Chinese characters by Korean native speakers involve neural mechanisms that are similar to Chinese native speakers; i.e. strong left-lateralized middle frontal cortex activation. For the case of Korean word reading, the activation pattern in the bilateral fusiform gyrus, left middle frontal gyrus, left superior temporal gyrus, right mid temporal gyrus, precentral gyrus, and insula was observed. This suggests that the activation pattern for Korean word reading appears to corroborate with that of alphabetic words at the general level. A further noteworthy finding of our study is the strong activation of the posterior part of the right dorsolateral prefrontal cortex (BA 8). The right hemispheric BA 8 belongs to the visual higher order control area and we propose that this area should be responsible for processing of visuospatial (surface form) information of Korean words. (C) 2004 Elsevier Ireland Ltd. All rights reserved
Analysis of functional MRI data based on an estimation of the hemodynamic response in the human brain
No full textFunctional magnetic resonance imaging (fMRI) data is usually analyzed using hemodynamic response data formulated with the aid of a gamma function. An fMRI response to stimuli can be mathematically modeled by convolution of the hemodynamic response and the presented stimulus. This approach is based on a linear system analysis. However, it is known that most biological systems are nonlinear and the nature of the hemodynamic response depends on both the subjects and brain regions under study. In this work, we estimated the hemodynamic responses of the fusiform face area (FFA) and the primary visual area (VI) using 1st- and 2nd-order Volterra kernels. The estimated hemodynamic responses were used to analyze fMRI data obtained from the corresponding regions. The results of the analysis of fMRI data using the estimated hemodynamic responses show a more significant activation than is obtained by conventional analysis using the hemodynamic response modeled by gamma function. (C) 2004 Published by Elsevier B.V
Neural correlates of eye blinking; improved by simultaneous fMRI and EOG measurement
No full textNeural correlates of eye blink in healthy human subjects can be investigated using functional magnetic resonance imaging. However, the focus of most previous studies has been on intentional eye blinking. The goal of the present study was to examine the neural correlates of spontaneous eye blinking with the help of EOG measurements during data acquisition of fMRI. After the removal of the pulse artifact in the EOG signal, EOG waveform clearly indicates eye blinking, which was equivalent to those measured outside of the MRI scanner. On the basis of this detection, each blinking event can be used as a temporal cue for the event-related fMRI. In a comparison, we also investigated the neural correlates of blink inhibition. Based on the brain activation pattern, the activation of the bilateral parahippocampal, the visual cortex was commonly observed for both conditions. The additional activation of the precentral gyrus, corresponding to blink inhibition, and the right medial frontal gyrus, corresponding to spontaneous blinking were observed. Based on these results, we conclude that the medial frontal gyrus is responsible for spontaneous eye blinking, whereas precentral activation appears to be related to blink inhibition. (c) 2005 Elsevier Ireland Ltd. All rights reserved
An fMRI study of Chinese character reading and picture naming by native Korean speakers
Full text linkChinese characters appear in the currently used Korean language, and the system used for writing system the Korean language consists of a mixture of the Korean alphabet and Chinese characters. In the present study, neural mechanisms involved in reading a single Chinese character words and naming pictures by Korean native speakers were investigated using a functional magnetic resonance imaging technique. The findings show a right hemispheric dominance within the occipito-temporal and the left middle/medial frontal area for both reading Chinese characters and naming pictures. This should reflect the specific visual processing of reading Chinese characters. Additional activations in inferior frontal and cingulage gyrus were also observed. The activations of inferior parietal region and thalamus are of interest, since we assume that these activations are strongly related to the phonological status of single Chinese character words rather than two character words that are typically used by Korean native speakers. (C) 2005 Elsevier Ireland Ltd. All rights reserved
Susceptibility Compensated fMRI Study Using a Tailored RF Echo Planar Imaging Sequence
No full textPurpose: To implement a method using a tailored radiofrequency (TRF) pulse with a quadratic phase profile to recover susceptibility-induced signal losses in gradient-recalled echo-planar images (EPI). Materials and Methods: A functional magnetic resonance imaging (fMRI) experiment for compensation of susceptibility artifacts. known as the TRIF pulse EPI sequence (TRF-EPI), was used. TRF pulse compensates the susceptibility effect with a reduced signal-to-noise ratio (SNR) to one-half when the maximum phase distribution is 2 pi. We demonstrate theoretically that the maximum phase distribution can also be reduced to 7 rather than 2 pi. improving the SNR accordingly. An analysis was conducted comparing this newly proposed strategy using a standard RF excitation with a linear phase distribution and a quadratic TRF excitation with a pi phase distribution. Results: Thorough experimental comparisons were also made between the TRF quadratic excitation with a pi phase profile and conventional EPI with a standard excitation in human subjects during ventral brain activation. Conclusion: With reduced maximum phase distribution in the TRF pulse. signals in the susceptibility-affected areas, such as the orbitofrontal and interior temporal cortex. were increased. suggesting that the technique Could be a useful adjunct to fMRI.MOST(Korean Ministry of Science and Tech-nology); Contract grant numbers; M10530010001-06N3001-00110 and M1053001002-06N3001-00210
Neural mechanism of reading Chinese characters and pictures by Korean native speakers
No full textInternational Society for Magnetic Resonance in Medicine, Paper #1145, Kyot
Event related fMRI studies of voluntary and inhibited eye blinking using a time marker of EOG
Full text linkElectrooculogram (EOG) measurements, along with infrared measurements, are commonly used to record eye blinking during functional magnetic resonance imaging (fMRI). We report herein, on the use of EOG in measuring voluntary and inhibited eye blinking during echo planar imaging (EPI) in an MR scanner. The inhibited eye blinking occurred during the period, in which subjects were requested not to blink their eyes. After the removal of gradient-field induced artifacts from the EOG signal, the waveform of the EOG clearly showed both voluntary and inhibited eye blinking. Using these data, each voluntary or inhibited eye-blinking event was used as the temporal cue for all event related fMRI. Activation of the bilateral parahippocampal, precentral gyrus and left supplementary motor area was observed for voluntary eye blinking, whereas the medial/superior frontal, precentral, cingulate, precuneus, and superior temporal gyrus appears to be involved in inhibited eye blinking. Based on these experimental results, we propose that the precentral gyrus is responsible for both voluntary and inhibited eye blinking. The parietal area (precuneus and superior temporal gyrus) appears to be exclusively related to inhibited eye blinking. (c) 2005 Elsevier Ireland Ltd. All rights reserved
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