Biomedical subjects

Chikako Kato

Publications and source records attributed to Chikako Kato.

14 recordsLinked to original sources

PubMed2006

Dynamic monitoring of brain activation under visual stimulation using fMRI--the advantage of real-time fMRI with sliding window GLM analysis.

An fMRI technique based on real-time analysis was applied to evaluate the advantages of dynamic monitoring of the t-statistics based on a general linear model. The temporal change of the t-statistics in V1 and V4 under four conditions of visual stimuli covering different visual fields with or without coloring was estimated using an incremental analysis and a sliding window analysis (SWA). The SWA not only visualized the dynamic change of the activation in response to the task conditions and switching, but also enabled us to evaluate the temporal correlation of the t-statistics among the four visual areas. It was suggested that the activity in the V4 was bilaterally organized, and the altering color stimuli gave stronger stimulation to the V1 than did the black and white stimuli. Although the activation map at each time point represents the brain activity during several task and rest blocks, a SWA will be useful to evaluate the transition of neuronal activation in response to several sequential task conditions. An incremental analysis will be useful to monitor the ongoing activation in real-time during the scan, since it gives a higher t-value according to the accumulation of volume data. These two methods will be complementary.

Adult↗

PubMed2005

Temporal relationship between action and visual outcome modulates brain activation: an fMRI study.

Monitoring the visual outcome of our actions is critical to our visuo-motor behavior. To investigate the neural basis of monitoring visual change produced by self-movement, we examined the temporal relationship between manual depression of a button and visual feedback on activation of the brain. Six neurologically normal subjects participated in 3 experiments (synchronous, delayed, and visual [control]). Magnetic resonance (MR) images of their brains were acquired during the experiments using a scanner operating at 3T. In the synchronous experiment, subjects pressed a button at self-paced intervals and received synchronous visual stimuli in response. In the delayed experiment, visual stimuli were presented with a delay after subjects pressed a button at self-paced intervals. In the control experiment (visual experiment), subjects did not press the button, but viewed visual stimuli generated by a computer at random intervals. In the synchronous experiment, activation in the cerebellum and right parietal lobe was stronger than in the delayed experiment, whereas activation in the primary visual cortex was weaker than in the delayed and visual experiments. These results suggest that visual outcomes produced synchronously with action are processed in the cerebellum and the parietal area for the organization of optimal motor behavior, rather than in the primary visual area that is known to process the visual properties of external objects. The cerebellar signal related to visuo-motor contingency may modulate the cortical processing of visual input that is synchronous with action.

Adult↗

PubMed2005

An FMRI study to investigate auditory attention: a model of the cocktail party phenomenon.

In human life, discrimination of a target voice from other voices or sounds is indispensable, and inability for such discrimination results in sensory aphasia. To investigate the neuronal basis of the attentional system for human voices, we evaluated brain activity during listening comprehension tasks using functional magnetic resonance imaging (fMRI) at 3T. Diotic listening comprehension tasks, in which a narration was superimposed by another given by the same speaker (SV experiment) or by a different speaker (DV experiment), were presented to normal volunteers. The story indicated in the baseline task blocks, in which only one narration was presented, was intensively followed during the superimposed task blocks. In each experiment, 6 task blocks, 3 blocks for each condition, and 7 rest blocks were alternatively repeated, and the contrast of the superimposed condition to the baseline condition in each session was obtained. In the DV experiment, compared with the control condition, activation in Wernicke's area (BA22) was increased. In the SV experiment, activation in the frontal association cortex (BA6, BA9/ 46, BA32, BA13/47) was additionally increased. These results suggested that difficulty in phonological processing to discriminate human voices calls for further semantic, syntactic, and prosodic processing, as well as augmented selective attention.

Acoustic Stimulation↗

PubMed2004

Quantitative analysis of cellular fetal hemoglobin gamma chain messenger RNA (HbF-gamma mRNA) in maternal peripheral blood.

OBJECTIVE: Fetal cells cross the feto-maternal barrier and circulate in maternal peripheral blood; thus, this study aimed to show the relationship between clinical evidence in pregnancy and qualitative feto-maternal barrier changes. METHODS: The expression of fetal hemoglobin gamma chain messenger RNA (HbF-gamma mRNA) was measured by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in maternal peripheral blood. RESULTS: HbF-gamma mRNA was detected in all pregnant women after 5 weeks of gestation. In normal pregnancy, there were two peaks at 10 and 40 weeks, and a significant increase 4 weeks prior to the onset of labor. In intrauterine growth restriction (IUGR), preterm delivery and placenta previa, the HbF-gamma mRNA expression was significantly higher than in normal pregnancies. CONCLUSION: The expression of HbF-gamma mRNA relative to that of beta-actin mRNA is thought to reflect the real-time leakage of fetal cells into maternal blood.

Case-Control Studies↗

PubMed2004

Application of independent component analysis to magnetic resonance imaging for enhancing the contrast of gray and white matter.

An application of independent component analysis (ICA) was attempted to develop a method of processing magnetic resonance (MR) images to extract physiologically independent components representing tissue relaxation times and achieve improved visualization of normal and pathologic structures. Anatomical T1-weighted, T2-weighted and proton density images were obtained from 10 normal subjects, 3 patients with brain tumors and 1 patient with multiple sclerosis. The data sets were analyzed using ICA based on the learning rule of Bell and Sejnowski after prewhitening operations. The three independent components obtained from the three original data sets corresponded to (1) short T1 components representing myelin of white matter and lipids, (2) relatively short T1 components representing gray matter and (3) long T2 components representing free water. The involvement of gray or white matter in brain tumor cases and the demyelination in the case of multiple sclerosis were enhanced and visualized in independent component images. ICA can potentially achieve separation of tissues with different relaxation characteristics and generate new contrast images of gray and white matter. With the proper choice of contrast for the original images, ICA may be useful not only for extracting subtle or hidden changes but also for preprocessing transformation before clustering and segmenting the structure of the human brain.

Adolescent↗

PubMed2004

Expression of IL-4, IL-8 and IL-18 messenger RNAs in maternal peripheral blood and relationships with the HbF-gamma chain mRNA in it.

PROBLEM: This study was designed to examine immunological changes in maternal peripheral blood and the relationship of these changes with the amount of fetal cells in the blood. METHOD OF STUDY: The expression of interleukin-4 (IL-4), IL-8, IL-18 and fetal hemoglobin gamma chain (HbF-gamma chain) messenger RNAs (mRNAs) in maternal peripheral blood was measured by a quantitative reverse transcription-polymerase chain reaction method. RESULTS: In maternal peripheral blood, the expression of IL-4 mRNA was up-regulated from the second gestational month (GM) to delivery. The expression of IL-8 and IL-18 mRNAs was down-regulated from the third or fourth GM until the eighth or ninth GM, respectively, and both increased before the onset of labor, though IL-4 mRNA decreased. The expression of IL-8 and IL-18, but not IL-4, mRNAs was correlated with that of HbF-gamma chain mRNA. CONCLUSIONS: Immunological interactions between maternal peripheral immune cells and fetal cells appear to be related to the onset of labor.

Female↗

PubMed2004

MFB-1, an F-box-type ubiquitin ligase, regulates TGF-beta signalling.

TGF-beta signalling regulates cell growth, differentiation, morphogenesis and apoptosis. MAFbx/Atrogin-1 has been identified as a regulator for skeletal muscle atrophy and encodes an F-box-type E3 ubiquitin ligase. However, little is known about how MAFbx/Atrogin-1 regulates cellular signalling. Here, we identify and genetically characterize MFB-1, a MAFbx/Atrogin-1 homologue from Caenorhabditis elegans. The mfb-1 deletion mutant significantly enhanced the dauer constitutive (Daf-c) phenotype caused by mutations in the DAF-7/TGF-beta-like signalling pathway, but not the DAF-2/insulin receptor-like signalling pathway. Conversely, the Daf-c phenotypes of DAF-7 pathway mutants were partially suppressed by mfb-1 cDNA transgenes. Therefore, MFB-1 acts genetically downstream in the DAF-7 pathway. A mfb-1::GFP fusion was found to be expressed in the nervous system, hypodermis and intestine and overlapped expression of many DAF-7 pathway genes. We propose that MFB-1 is a novel F-box protein that negatively regulates dauer formation in concert with the DAF-7 signalling pathway in C. elegans.

Amino Acid Sequence↗

PubMed2003

A functional magnetic resonance imaging study of internal modulation of an external visual cue for motor execution.

The strategy to perform a task differs according to how a cue is interpreted. In order to investigate the basic mechanisms of temporal regulation in the higher motor areas, the interaction between two different types of internal modulations of an external visual cue was evaluated using functional magnetic resonance imaging (fMRI). An opposing finger movement task guided by dot prompting was employed. In the intermittent tapping experiment, two taps per second and a rest for one second were alternatively repeated in the task blocks. In the constant tapping experiments, the volunteers performed finger movements at 0.5, 1 or 2 Hz. The activation in the primary sensory motor area correlated with the amount of movement. Activities in the supplementary motor area, left dorsal pre-motor area, left superior parietal lobule and right cerebellum depended on the demand for internal modulation. Activation in these areas was maximum for the intermittent task which was a combination of two different internal modulations, and minimum for the 1 Hz movement that did not require internal modulation. It was suggested that these four areas are directly involved in the generation of a complex movement sequence driven by a visual cue, and they are organized for performance. The translation of external pacing and initiation for self-pacing may share the same neuronal basis. Activation in the left supramarginal gyrus, bilateral frontal operticula and basal ganglia did not depend on the combination of the two internal modulations.

Adult↗

PubMed2003

Discrimination of Exner's area and the frontal eye field in humans--functional magnetic resonance imaging during language and saccade tasks.

In the left frontal lobe, Exner's area (EXA), which is responsible for writing and reading, is located close to the frontal eye field (FEF), which is responsible for eye movements. To discriminate EXA from FEF anatomically and functionally, functional magnetic resonance imaging was conducted in 12 healthy volunteers. The saccadic eye movement experiment activated a region defined as the FEF, whereas three language experiments that included translation between grapheme and phoneme activated another region defined as EXA. EXA was found to be located only 1.5 cm apart from the FEF in the Talairach brain template. By conducting the saccade and language experiments in the same individuals, this study was able to successfully separate EXA from FEF.

Adult↗

PubMed2003

Orthography effect on brain activities in the working memory process for phonologically ambiguous syllables: a functional magnetic resonance imaging study using Japanese speakers.

English /l/ and /r/ sounds are not distinctive for Japanese speakers and they are loosely associated with corresponding graphemes. The purpose of this study was to investigate the brain activities in the memory process for the graphemes containing 'l' and 'r' in Japanese speakers. Two functional magnetic resonance imaging (at 1.5 T) experiments was conducted using syllable working memory tasks. The task using 'l' and 'r' syllables was coupled with either task using 'b' and 'n' syllables (l/r versus b/n block-designed experiment), or 'd' and 'n' syllables (l/r versus d/n block-designed experiment). The results revealed that the l/r working memory tasks induced augmented activation specifically in the right middle frontal gyrus (BA9, 46) and the right superior parietal lobule (BA7), compared with the b/n or d/n tasks. The results indicate that a visually-biased memory process (i.e. excessive visual rehearsal or monitoring) was executed for phonologically ambiguous syllables. Significant activation in the left inferior frontal gyrus was not observed only in the b/n task, probably because articulatory contrast between /b/ and /n/ sounds was highly clear for Japanese speakers.

Adult↗

PubMed2003

The effect of task block arrangement on the detectability of activation in fMRI.

The effect of task block arrangements on the detection of brain activation was investigated. Sessions of functional magnetic resonance imaging (fMRI) including the same number of two different task conditions but with different arrangements were compared. The two task conditions were, A) Ellipse-shaped black and white checkerboard flicker stimulation at 4.2 Hz covering the bilateral visual field, and B) the same flicker stimuli covering only the left visual field. In the rest blocks (0), the subjects looked at a fixation point. Four different task block arrangements were compared, 1) A0 (0A0A0A0) and B0 (0B0B0B0), 2) A0B0 (0A0B0A0B0A0B0), 3) AB0 (0AB0AB0AB0) and 4) AB (0ABABAB). Bilateral V1, V2, V3 and the left V5 were activated by condition A, and the right V1 and V2 by B. The activation in the left visual field by A0 was larger than in the other three conditions. In a differential analysis between conditions A and B, activation in the left V3 and V5 was declined by AB0 or AB. When rest blocks were located in the post-stimulus undershoot phase, the % signal change of the BOLD signal was emphasized, which caused augmented significance in the detection of the activity. It was indicated that the outcome of the activation map was influenced by the arrangement of task blocks, even though the same number of task blocks were repeated within the sessions. In fMRI studies, task conditions should be carefully compared within or across sessions considering the characteristics of hemodynamic response functions.

Adult↗

PubMed2003

Finger movements lighten neural loads in the recognition of ideographic characters.

The role of finger writing movements in recognizing Japanese ideographic characters (Kanji) was investigated using functional magnetic resonance imaging at 3 T. A total of 12 healthy native Japanese-speaking volunteers were studied while counting the number of strokes in ideographic characters. In experiment 1, a representation of the pronunciation of an ideographic character was displayed using Japanese syllabic characters. Volunteers were required to count the strokes of the ideographic character corresponding to the displayed phonogram. This procedure included retrieval and generation of ideographic characters. In experiment 2, the ideographic character itself was displayed and the volunteers counted its strokes. This procedure focused on visuospatial imagery processes. Each experiment was conducted under two different motor conditions. One condition allowed the subject to use finger movements to count the strokes, while the other disallowed any finger movements. In both experiments, movement-allowed conditions duly activated the primary motor area. The phonogram-displayed and movement-disallowed condition induced an augmented activation in a part of the left premotor area, which was assumed to be Exner's area. This area might have been activated by a demand for sequential generation of character graphemes that corresponded to the phonogram displayed. The ideographic-character-displayed and movement-disallowed condition activated the dorsal occipitoparietal areas and the primary visual area, which might be involved in the visuospatial mental imagery processes. These results suggest that execution of finger movements during stroke counting of ideographic characters lightens the neural loads for grapheme generation on Exner's area and for the visuospatial imagery processes on the dorsal pathway.

Adult↗

PubMed2002

Generation, characterization, and heterologous expression of wild-type and up-regulated forms of Arabidopsis thaliana leaf ADP-glucose pyrophosphorylase.

ADP-glucose pyrophosphorylase (AGPase), a key enzyme in starch biosynthesis of higher plants, consists of a pair of regulatory large (LS) and catalytically small (SS) subunits. In plants, these subunits are coded by multiple genes resulting in the formation of tissue-specific enzyme forms, which are differentially regulated during plant growth and development. Some AGPase isoforms differ in catalytic and regulatory properties as well as intracellular location. In an effort to gain a better understanding of the role of the leaf AGPase in carbon partitioning and its effect on plant productivity, the Arabidopsis leaf AGPase containing the mature forms of the SS and LS was expressed in a heterologous expression system and characterized enzymatically. The Arabidopsis recombinant AGPase had kinetic values for 3-phosphoglyceric acid, glucose-1-phosphate and Mg(2+) similar to those of the native enzyme. As the N-terminus of the LS has been suggested to be involved in enzyme function, the length of the N-terminal region was extended or shortened. Of the five modified LSs analyzed, only the T5 form lacking six residues of the mature N-terminus was able to form detectable levels of enzyme activity, indicating that the N-terminal region is critical for enzyme function. Two up-regulatory LS mutations that allosterically activate the potato enzyme, a stem isoform, were introduced into the corresponding Arabidopsis LS sequences and co-expressed with wild-type SS. Both modified enzymes showed up-regulatory properties, indicating that these specific residue changes were also operational in the leaf isoform.

Amino Acid Sequence↗

PubMed2002

Manipulo-spatial processing of ideographic characters in left-handers: observation in fMRI.

It has been suggested that left-handers have a cerebral ambilaterality for language representation. Specifically, the use of the right hand for writing may have a specific effect on the cerebral organization in left-handers. In an investigation of the relationship between motor and visual language procedures, functional magnetic resonance imaging at three tesla was conducted during stroke counting of kanji (Japanese ideographic characters) in six left-handers who usually write with their right hand. Two types of stimulus presentation, phonography-displayed and kanji-displayed, were employed to examine the different neural pathways used for processing kanji. Each stimulus presentation involved two motor conditions: one allowed finger movements for tracing the characters, while the other disallowed finger movements. The tasks induced activation in the primary motor area, the premotor area, the supplementary motor area, and the anterior cingulate gyrus as well as the parietal and occipital lobes (Brodmann's area 7/39/19). The activated areas in both the movement-allowed and movement-disallowed conditions were almost identical except for the primary motor area. These results clearly contrasted with those of a previous study of right-handers which showed that right-handed volunteers demonstrated decreased activation in the premotor area and the dorsal pathway during the movement-allowed condition. This discrepancy may be attributable to a difference in cerebral organization for language processing. Specifically, in left-handers, the visuospatial procedure for kanji and the motor procedure for tracing the kanji may be ambilaterally distributed in both hemispheres, whereas in right-handers these procedures may be predominantly lateralized in the left hemisphere.

Acoustic Stimulation↗