Biomedical subjects

Jen-Chuen Hsieh

Publications and source records attributed to Jen-Chuen Hsieh.

34 records · Page 2Linked to original sources

PubMed2004

Orthographic and phonological processing of Chinese characters: an fMRI study.

The present study used functional magnetic resonance imaging (fMRI) to investigate the neural mechanisms underlying the orthographic and phonological processing of Chinese characters. Four tasks were devised, including one homophone judgment and three physical judgments of characters, pseudo-characters, and Korean-like nonsense figures. While the left occipitotemporal region, left dorsal processing stream, and right middle frontal gyrus constitute a network for orthographic processing, the left premotor gyrus, left middle/inferior frontal gyrus, supplementary motor area (SMA), and the left temporoparietal region work in concert for phonological processing. The ventral part of the left inferior frontal cortex responds specifically to the character stimuli, suggesting a general lexical processing role for this region for linguistic material. The stronger activation of the dorsal visual stream by Chinese homophone judgment pinpoints a tight coupling between phonological representation of Chinese characters and corresponding orthographic percepts. The concomitant engagement of sets of regions for different levels of Chinese orthographic and phonological processing is consistent with the notion of distributed parallel processing.

Adult↗

PubMed2004

Neuronal correlates of consistency and frequency effects on Chinese character naming: an event-related fMRI study.

This event-related functional magnetic resonance imaging (efMRI) study aims to investigate the central representations of Chinese orthography-to-phonology transformation (OPT) by simultaneously manipulating character frequency and consistency. Bilateral inferior frontal cortices (including Broca's area and insula), the left temporoparietal region (superior parietal gyrus and supramarginal gyrus), and the left temporal-occipital junction showed greater activation, especially in low-frequency conditions, when naming inconsistent characters as compared to consistent ones. These findings suggest that these regions are involved in the sublexical conversion of orthographic input into phonological codes in naming Chinese. The similar activation pattern found in these three regions suggests a distributed process, rather than separate neural routes, for lexical and sublexical OPT. In addition, the regions involved in Chinese OPT are congruent with the findings for reading alphabetic scripts and indicate that the neuronal mechanisms for orthography-to-phonology transformation is domain universal across different writing systems.

Adult↗

PubMed2003

Healthy-side dominance of cortical neuromagnetic responses in sudden hearing loss.

Previous brain imaging and mapping studies have reported findings indicating functional reorganization in the central auditory pathways of patients with profound unilateral hearing loss. This study reports for the first time to our knowledge, using a whole-head neuromagnetometer with monaural stimulation of both intact and affected ears, a pattern of healthy-side dominance for cortical neuromagnetic responses in adult patients in the early stage of idiopathic sudden sensorineural hearing loss, and a pattern of contralateral dominance is verified in controls.

Adult↗

PubMed2003

Hemodynamic segmentation of MR brain perfusion images using independent component analysis, thresholding, and Bayesian estimation.

Dynamic-susceptibility-contrast MR perfusion imaging is a widely used imaging tool for in vivo study of cerebral blood perfusion. However, visualization of different hemodynamic compartments is less investigated. In this work, independent component analysis, thresholding, and Bayesian estimation were used to concurrently segment different tissues, i.e., artery, gray matter, white matter, vein and sinus, choroid plexus, and cerebral spinal fluid, with corresponding signal-time curves on perfusion images of five normal volunteers. Based on the spatiotemporal hemodynamics, sequential passages and microcirculation of contrast-agent particles in these tissues were decomposed and analyzed. Late and multiphasic perfusion, indicating the presence of contrast agents, was observed in the choroid plexus and the cerebral spinal fluid. An arterial input function was modeled using the concentration-time curve of the arterial area on the same slice, rather than remote slices, for the deconvolution calculation of relative cerebral blood flow.

Adolescent↗

PubMed2003

ICA-based spatiotemporal approach for single-trial analysis of postmovement MEG beta synchronization.

The extraction of event-related oscillatory neuromagnetic activities from single-trial measurement is challenging due to the non-phase-locked nature and variability from trial to trial. The present study presents a method based on independent component analysis (ICA) and the use of a template-based correlation approach to extract Rolandic beta rhythm from magnetoencephalographic (MEG) measurements of right finger lifting. A single trial recording was decomposed into a set of coupled temporal independent components and corresponding spatial maps using ICA and the reactive beta frequency band for each trial identified using a two-spectrum comparison between the postmovement interval and a reference period. Task-related components survived dual criteria of high correlation with both the temporal and the spatial templates with an acceptance rate of about 80%. Phase and amplitude information for noise-free MEG beta activities were preserved not only for optimal calculation of beta rebound (event-related synchronization) but also for profound penetration into subtle dynamics across trials. Given the high signal-to-noise ratio (SNR) of this method, various methods of source estimation were used on reconstructed single-trial data and the source loci coherently anchored in the vicinity of the primary motor area. This method promises the possibility of a window into the intricate brain dynamics of motor control mechanisms and the cortical pathophysiology of movement disorder on a trial-by-trial basis.

Adult↗

PubMed2003

Frequency effects of Chinese character processing in the brain: an event-related fMRI study.

Knowing how the brain processes Chinese characters of different frequencies of occurrence may shed light on the extent to which orthographic variations of different languages can influence reading processes in the brain. In the present study, event-related fMRI was used to investigate frequency effects on Chinese character processing. Reading low-frequency characters invoked higher activation in several brain regions including the left premotor/inferior frontal gyrus, supplementary motor area, left anterior insula, left posterior inferior temporal gyrus, left superior parietal cortex, and lingual cortex, while reading high-frequency characters resulted in higher activation in the left supramarginal/angular gyrus and left precuneus. The activation pattern of reading infrequently encountered characters reflects a more demanding processing procedure of retrieving, formulating, and coordinating the phonological output. Access to the lexical route may benefit the reading of high-frequency characters. By uncovering the differential brain responses in reading Chinese characters of different occurrence frequencies, not only has a substantial overlap between functional neuroanatomy of reading Chinese and alphabetical languages been demonstrated, but also features permitting the separation of language-specific content from universal mechanisms.

Adult↗

PubMed2003

Differential effects of stimulus intensity on peripheral and neuromagnetic cortical responses to median nerve stimulation.

To study the differential effects of tactile stimulus intensity on cortical and peripheral responses, we measured neuromagnetic cortical responses, compound muscle action potentials (CMAP), sensory nerve action potentials (SNAP), and the subjective estimation of tactile magnitude to electric median nerve stimulation at the wrist in 13 male healthy adults. The sensory perception threshold (ST) for electric pulses at wrist skin was determined and then various levels of stimulus intensity (1 approximately 6 ST) were given to each subject. At 1 ST, only the P50m components of the primary somatosensory (SI) cortical responses were recorded. The second somatosensory (SII) cortical responses were saturated at 2 ST, while the SI responses reached maximum at 3 ST equivalent to the subjective threshold intensity for "strong" tactility. The CMAP and SNAP were maximum at 4-5 ST. At 2 ST, >70% of maximum SI responses were produced, whereas only <40% of maximum CMAP or SNAP responses were obtained. We concluded that the stimulus intensities for activating or saturating somatosensory cortical responses were lower than those for CMAP and SNAP. The differential intensity effects on cortical and peripheral responses suggest a polysynaptic organization underlying the central amplification for somatosensory cortical activation. The optimal intensity levels for producing maximum SI and SII responses were 3 and 2 ST, respectively. Compared with the SII, the SI plays a crucial role in the coding of the tactile stimulus intensity.

Action Potentials↗

PubMed2003

Magnetoencephalographic analysis of bilaterally synchronous discharges in benign rolandic epilepsy of childhood.

The purpose of this study was to examine the spatial and temporal relationship between bilateral foci of bilaterally synchronous discharges in benign rolandic epilepsy of childhood (BREC) using a whole-scalp neuromagnetometer. We simultaneously recorded interictal magnetoencephalographic (MEG) and electroencephalographic (EEG) signals in six children with BREC. Interictal spikes were classified into three groups: bilaterally synchronous discharges (BSDs), unilateral discharges on right side (UD-R), and unilateral discharges on left side (UD-L). We used equivalent current dipole (ECD) modelling to analyse the cortical sources of interictal spikes. Both BSDs and UDs were found in Patients 1-4, whereas only UDs were identified in Patients 5 and 6. The ECDs of interictal spikes were located in rolandic regions, 10-20mm anterior and lateral to hand somatosensory cortices. Multi-dipole analysis of BSDs showed two ECDs in homotopic motor areas of the hemispheres. During BSDs, the right-sided activation preceded the left-sided activation by 15-21 milliseconds in Patients 1 and 2. In Patients 3 and 4, the activation occurred 17-20 milliseconds earlier in the left than the right hemisphere. Within the same hemisphere, the sources of BSDs and UDs were located in similar areas. In conclusion, our results imply the cortical epileptogenicity in bilateral perirolandic areas in BREC. The sequential activation during BSDs in both hemispheres suggest the existence of synaptic connections, possibly via the corpus callosum, between bilateral irritative foci.

Brain Mapping↗

PubMed2003

Different central manifestations in response to electroacupuncture at analgesic and nonanalgesic acupoints in rats: a manganese-enhanced functional magnetic resonance imaging study.

Acupuncture analgesia is an important issue in veterinary medicine. This study was designed to elucidate central modulation effects in response to electroacupuncture (EA) at different acupoints. Manganese-enhanced functional magnetic resonance imaging was performed in Sprague-Dawley rats after sham acupuncture, sham EA, or true EA at somatic acupoints. The acupoints were divided into 3 groups: group 1, analgesic acupoints commonly used for pain relief, such as Hegu (LI 4); group 2, nonanalgesic acupoints rarely used for analgesic effect such as Neiguan (PC 6); and group 3, acupoints occasionally used for analgesia, such as Zusanli (ST 36). Image acquisition was performed on a 1.5-T superconductive clinical scanner with a circular polarized extremity coil. The results showed that there was no neural activation caused by EA at a true acupoint with shallow needling and no electric current (sham acupuncture). When EA at a true acupoint was applied with true needling but no electric current (sham EA), there was only a slight increase in brain activity at the hypothalamus; when EA was applied at a true acupoint with true needling and an electric current (true EA), the primary response at the hypothalamus was enhanced. Also, there was a tendency for the early activation of pain-modulation areas to be prominent after EA at analgesic acupoints as compared with nonanalgesic acupoints. In conclusion, understanding the linkage between peripheral acupoint stimulation and central neural pathways provides not only an evidence-based approach for veterinary acupuncture but also a useful guide for clinical applications of acupuncture.

Acupuncture Analgesia↗

PubMed2002

Loss of interhemispheric inhibition on the ipsilateral primary sensorimotor cortex in patients with brachial plexus injury: fMRI study.

This functional magnetic resonance imaging study verified an antagonistic pattern in which a concomitant deactivation of ipsilateral primary sensorimotor (SM1) was coupled to the contralateral SM1 activation in healthy controls during unimanual hand grasping. Of note, dramatic reduction of ipsilateral SM1 deactivation (loss of antagonistic pattern) was observed during movement of intact hands by patients with unilateral brachial plexus injury. We propose that the disappearance of the antagonistic pattern of SM1 activities in the patients with brachial plexus injury reflects a reduction of interhemispheric inhibition, which may mirror an adaptive mechanism to functional status.

Adult↗

PubMed2002

Single-trial variability in event-related BOLD signals.

Most current analysis methods for fMRI data assume a priori knowledge of the time course of the hemodynamic response (HR) to experimental stimuli or events in brain areas of interest. In addition, they typically assume homogeneity of both the HR and the non-HR "noise" signals, both across brain regions and across similar experimental events. When HRs vary unpredictably, from area to area or from trial to trial, an alternative approach is needed. Here, we use Infomax independent component analysis (ICA) to detect and visualize variations in single-trial HRs in event-related fMRI data. Six subjects participated in four fMRI sessions each in which ten bursts of 8-Hz flickering-checkerboard stimulation were presented for 0.5-s (short) or 3-s (long) durations at 30-s intervals. Five axial slices were acquired by a Bruker 3-T magnetic resonance imager at interscan intervals of 500 ms (TR). ICA decomposition of the resulting blood oxygenation level-dependent (BOLD) data from each session produced an independent component active in primary visual cortex (V1) and, in several sessions, another active in medial temporal cortex (MT/V5). Visualizing sets of BOLD response epochs with novel BOLD-image plots demonstrated that component HRs varied substantially and often systematically across trials as well as across sessions, subjects, and brain areas. Contrary to expectation, in four of the six subjects the V1 component HR contained two positive peaks in response to short-stimulus bursts, while components with nearly identical regions of activity in long-stimulus sessions from the same subjects were associated with single-peaked HRs. Thus, ICA combined with BOLD-image visualization can reveal dramatic and unforeseen HR variations not apparent to researchers analyzing their data with event-related response averaging and fixed HR templates.

Adult↗

PubMed2002

Event-related functional MRI study on central representation of acute muscle pain induced by electrical stimulation.

Although pathological muscle pain involves a significantly larger population than any other pain condition, the central mechanisms are less explored than those of cutaneous pain. The aims of the study were to establish the pain matrix for muscle pain in the full head volume and, further, to explore the possibility of a functional segregation to nonpainful and painful stimuli within the area of the parasylvian cortex corresponding to the secondary somatosensory area. Additionally, we speculate that a randomization of nonpainful and painful stimuli may target specific structures related to stimulus salience. We used event-related functional magnetic resonance imaging (MRI) and the high sensitivity of the 3-T MRI scanner to study the central processing of acute muscle pain induced by intramuscular electrostimulation. Brief nonpainful and painful stimuli (1-ms duration, interstimulus interval = 12 s) were randomly applied to the left abductor pollicis brevis of 10 subjects. The data disclose a pain matrix for muscle pain similar to that for cutaneous pain. Individual analysis suggests separate representations within the area bounded by the upper bank of the Sylvian fissure (SF) and the circular sulcus of insula (CSI). Nonpainful stimulation activated the superficial parietal operculum adjoining the SF, while the painful condition additionally targeted the deeper parietal operculum bordering the CSI. Randomization of stimuli of different intensities likely introduces cognitive components that engage neural substrates servicing the appreciation of stimulus salience in the context of affect-laden pain imposition.

Acute Disease↗

PubMed1996

Traumatic nociceptive pain activates the hypothalamus and the periaqueductal gray: a positron emission tomography study.

The study was conducted to investigate which areas of the brain respond to a painful encounter of minor dermal injury (a model of clinical pain) elicited by intracutaneous injection of a minute amount of ethanol. Four healthy volunteers (27-46 years) were subjected to positron emission tomographic (PET) investigation of regional cerebral blood flow (rCBF), using [15O]butanol as tracer. The ethanol (20 microliters, 70%) and saline (20 microliters, 0.9%) were injected intracutaneously 3 times in a single-blinded, semi-randomised manner for the pain experiment. All the injections were performed, adjacent to each other, at the lateral aspect of the right upper arm. Subjective sensory intensity of pain, unpleasantness and anxiety were rated with separate 100-mm visual analogue scales together with the Spielberger's State Anxiety Inventory (Spielberger et al. 1970) and heart rate. Paired-subtraction (pixel-by-pixel) between ethanol and saline was performed. Traumatic pain significantly caused higher ratings of intensity and affect scales, i.e., pain intensity, unpleasantness and increased sympathetic activity (evidenced by tachycardia). In contrast the anxiety rating remained unchanged. Acute traumatic nociceptive pain prominently activated the hypothalamus and periaqueductal gray (PAG). In addition, activations of the prefrontal cortex (PFC), insular, anterior cingulate cortex (ACC), posterior parietal cortex (PPC), primary motor/somatosensory areas (MI/SI: face, upper arm), supplementary motor area (SMA), and cerebellum were also demonstrated. The central processing of the pain-relevant/anticipatory arousal also engaged the PAG. This study demonstrates the involvement of the human cerebral cortex in perception, arousal, cognitive evaluative processes, and, hence, affective reactions (somatic/ autonomic outflow) associated with pain. The pain stimulus of traumatic character may, by its very nature, evoke the central processing to involve both the hypothalamus and the PAG.

Adult↗

PubMed1996

Right-lateralised central processing for pain of nitroglycerin-induced cluster headache.

Recent functional brain imaging studies with positron emission tomography (PET) suggest a preference of the right hemisphere, especially the anterior cingulate cortex (ACC), in affective processing of the clinical pain syndromes. We have investigated the central processing of cluster headache (CH) attacks provoked by sublingual nitroglycerin (NTG). In the cerebrum, provoked CH activated the ACC and the temporopolar region of the right hemisphere in addition to other regions. The regions activated in the ACC (Brodmann area (BA) 24 and 32) are involved in affective/cognitive processing of pain and willed attention. Our study discloses the preferential role of the right hemisphere in attributing emotional valence and attention to the suffering of pain. The findings support the theory of a right hemispheric specialisation in the mediation of withdrawal-related negative affect. The divergence of the distributed central processing between provoked cluster headache attack and experimentally induced acute pain indicates different central mechanisms for different types of pain.

Adult↗

PubMed1995

Central representation of chronic ongoing neuropathic pain studied by positron emission tomography.

This study was undertaken to explore whether the neural substrates demonstrated in brain imaging studies on experimentally induced pain are involved in the perception of chronic neuropathic pain. We investigated the cerebral representation of chronic lateralised ongoing pain in patients with painful mononeuropathy (PMN, i.e., pain in the distribution of a nerve, neuralgia) with positron emission tomography (PET), using regional cerebral blood flow (rCBF) as an index for neuronal activity. Eight patients (29-53 years) with PMN in the lower extremity (4 in the right, 4 in the left) were recruited. Paired comparisons of rCBF were made between the patient's habitual pain (HP) state and the pain alleviated (PA) state following a successful regional nerve block (RNB) with lidocaine. The ongoing neuropathic pain resulted in activation of bilateral anterior insula, posterior parietal, lateral inferior prefrontal, and posterior cingulate cortices as well as the posterior sector of the right anterior cingulate cortex (ACC), Brodmann area (BA) 24, regardless of the side of PMN. In addition, a reduction in rCBF was noted in the contralateral posterior thalamus. No significant change of rCBF was detected in the somatosensory areas, i.e., SI and SII. The cerebral activation pattern, while addressing the differences between the HP and PA states, emphasises the affective-motivational dimension in chronic ongoing neuropathic pain. The striking preferential activation of the right ACC (BA 24), regardless of the side of the PMN, not only confirms that the ACC participates in the sensorial/affectional aspect of the pain experience but also suggests a possible right hemispheric lateralisation of the ACC for affective processing in chronic ongoing neuropathic pain. Our data suggests that the brain employs different central mechanisms for chronic neuropathic pain and experimentally induced acute pain, respectively.

Adult↗

PubMedDate not supplied

Toward normal perfusion after radiosurgery: perfusion MR Imaging with independent component analysis of brain arteriovenous malformations.

BACKGROUND AND PURPOSE: Brain perfusion is disturbed by cerebral arteriovenous malformations (AVMs). Our study was conducted to determine the radiosurgical effects on this disturbed perfusion. METHODS: MR perfusion imaging with independent component analysis was performed in five healthy subjects and 19 patients with AVM before and after radiosurgery (every 6 months up to 2 years). Perfusion map relative cerebral blood volume (rCBV), cerebral blood flow (rCBF), and mean transient time (rMTT) were assessed. Regions of interest (ROIs) on AVM target sections were defined as follows: N, AVM nidus; H, the rest of the ipsilateral hemisphere; P, immediately posterior to the nidus; A, immediately anterior to the nidus; Ar, anterior remote; Pr, posterior remote. Similar ROIs in the contralateral hemisphere (N1, H1, P1, A1, Pr1, and Ar1) served as internal references. Perfusion ratios of ROI-ROI1 were defined. Nonparameteric Mann-Whitney U tests and generalized linear models were used for statistical analysis. RESULTS: Before radiosurgery, patients' H/H1 rCBV and rCBF ratios were significantly higher than those of healthy subjects (P < .005), indicating AVM steal. Three types of perilesional perfusion disturbance were observed. From the first postradiosurgical follow-up at 6 months, N/N1 rCBV and rCBF ratios gradually decreased to 1.0 (both P < .001), whereas rMTT ratios gradually increased to 1.0 (P < .015); H/H1, A/A1, and P/P1 rCBV and rCBF ratios decreased after radiosurgery (P < .005), indicating reversal of steal toward normal perfusion. CONCLUSION: Initial high transnidal flow and perinidal perfusion disturbances were demonstrated. They gradually changed toward normal perfusion after radiosurgery. This explains, in part, the pathophysiologic factors of AVM and therapeutic effects.

Adult↗