Biomedical subjects

I Shimoyama

Publications and source records attributed to I Shimoyama.

At least 19 recordsLinked to original sources

PubMed2006

Synaptic origin of the respiratory-modulated activity of laryngeal motoneurons.

To determine the synaptic source of the respiratory-related activity of laryngeal motoneurons, spike-triggered averaging of the membrane potentials of laryngeal motoneurons was conducted using spikes of respiratory neurons located between the Bötzinger complex and the rostral ventral respiratory group as triggers in decerebrate, paralyzed cats. We identified one excitatory and two inhibitory sources for inspiratory laryngeal motoneurons, and two inhibitory sources for expiratory laryngeal motoneurons. In inspiratory laryngeal motoneurons, monosynaptic excitatory postsynaptic potentials were evoked by spikes of inspiratory neurons with augmenting firing patterns, and monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked by spikes of expiratory neurons with decrementing firing patterns and by spikes of inspiratory neurons with decrementing firing patterns. In expiratory laryngeal motoneurons, monosynaptic IPSPs were evoked by spikes of inspiratory neurons with decrementing firing patterns and by spikes of expiratory neurons with augmenting firing patterns. We conclude that various synaptic inputs from respiratory neurons contribute to shaping the respiratory-related trajectory of membrane potential of laryngeal motoneurons.

Action Potentials↗

PubMed2002

A dual-channel FM transmitter for acquisition of flight muscle activities from the freely flying hawkmoth, Agrius convolvuli.

Moths can perform various flight maneuvers by the contraction of some direct and indirect flight muscles. Multi-channel recording from these flight muscles and analysis of their interaction is very important for understanding insect flight motor system. In this study, we developed a dual-channel FM transmitter for acquisition of muscle potentials, with which a male hawkmoth (Agrius convolvuli) could fly freely and perform pheromone triggered zigzag flight in a wind tunnel. The transmitter weighs only 0.25 g including single battery, has a 5 m receivable range and works for more than 30 min. Doubling channels was achieved by providing two oscillators (the carrier frequencies were 82 and 85 MHz), and interference between them was overcome by buffer amplifiers and independent reference electrodes for each channel. With this transmitter, we could acquire muscle potentials from some direct and indirect muscles during free flight. Combined with simultaneous high-speed video analysis, we observed distinct changes of motor patterns during takeoff. Our radio-telemetric system allows acquisition of actual information from freely flying moths; such information will lead to further progress in the study of insect flight.

Animals↗

PubMed2001

Photon-stimulated ion desorption from molybdenum oxides following Mo 2p3/2 excitation.

Photon-stimulated ion desorption from solid MoO3 following the Mo 2p3/2 resonant transition has been investigated. In the XANES spectrum, Mo 2p3/2 peak is split into two components corresponding to the excitations from Mo 2p3/2 into the t2g and e(g) orbitals. It was observed that the desorption yield of O+ ions at the Mo 2p3/2-->e(g) resonance is higher than that at the Mo 2p3/2-->t2g resonance. The Auger decay spectra reveal that there exist two kinds of spectator Auger decays. The high desorption yield at the 2p3/2-->e(g) resonance is interpreted by the fast breaking of the Mo-O bond due to the localization of the electrons in the highly antibonding e(g).

Journal Article↗

PubMed2000

Pseudogap formation in the intermetallic compounds (Fe1-xVx)3Al

Optical conductivity data of the intermetallic compounds (Fe1-xVx)3Al ( 0</=x</=0.33) reveal that their density of states around the Fermi energy ( E(F)) is strongly reduced as x is increased. In particular, Fe2VAl ( x = 0.33) has a deep, well-developed pseudogap of 0.1-0.2 eV at E(F) and a small density ( approximately 5x10(20) cm(-3)) of carriers, which is highly unusual for intermetallic compounds. It is shown that the pseudogap results from the band structure of Fe2VAl, rather than from temperature-dependent correlation effects. Based on the present results, we propose a simple model that consistently explains both the semiconductorlike transport and the metallic photoemission results previously observed for Fe2VAl.

Journal Article↗

PubMed2000

Gastric and non-gastric signals in electrogastrography.

Electrogastrography (EGG) is the cutaneous recording of gastric myoelectrical activity, and the dominant frequency reflects the rhythm of the gastric slow wave. Ambulatory EGG is contaminated with a large amount of motion artifacts, and it is unclear how much of the signals comprising the dominant frequency originates from non-gastric sources. The aim of the present study was to evaluate the pattern of gastric and non-gastric signals in the dominant frequency histogram (DFH) obtained from long-term ambulatory EGG recordings. Ten normal controls and five post-gastrectomy patients participated in the present study. Twenty-four hour ambulatory EGG was recorded under normal daily conditions. The DFH of normal controls showed two distinctive peaks, and that of the post-gastrectomy patients, a single peak. The common peak at approximately 1.5 cpm was seen in both DFHs, and the peak at 3 cpm was seen only in the DFH of normal controls. Thus, the common peak was thought to be a product of non-gastric origin. In conclusion, the dominant frequency consists of gastric and non-gastric components which have a specific distribution pattern in the DFH. These findings quantified the contribution of gastric and non-gastric signals to the dominant frequencies in long-term ambulatory EGG.

Adult↗

PubMed2000

Flash-related synchronization and desynchronization revealed by a multiple band frequency analysis.

The fast Fourier transform (FFT) is a good method to estimate power spectral density (PSD), but the frequency resolution is limited to the sampling window, and thus the precise characteristics of PSD for short signals are not clear. To relax the limitation, a multiple band-pass filter was introduced to estimate the precise course of PSDs for flash visual evoked potentials (VEPs). Signals were recorded during -200 and 600 ms using balanced noncephalic electrodes, and sampled at 1,000 Hz in 12 bits. With 1 Hz and 10 ms resolutions, PSDs were estimated between 10 and 100 Hz. Background powers at the alpha- and beta-bands were high over the posterior scalp, and powers around 200 ms were evoked at the same bands over the same region, corresponding to P110 and N165 of VEPs. Normalized PSDs showed evoked powers around 200 ms and suppressed powers following the evoked powers over the posterior scalp. The evoked powers above the 20 Hz band were not statistically significant, however, the gamma band was significantly evoked intra-individually; details in the gamma bands were varied among the subjects. Details of PSDs were complicated even for a simple task such as watching flashes; both synchronization and desynchronization occurred with different distributions and different time courses.

Adult↗

PubMed1999

Attention changes the peak latency of the visual gamma-band oscillation of the EEG.

To investigate the physiological role of visual gamma-band oscillation (GBO), we calculated the event-related dynamics of the EEG power-spectrum for paired visual stimuli (S1 and S2) with or without attention in 12 subjects. The visual stimuli elicited transient increases in the GBO power (around 40 Hz), which were maximal over the parietal area. The peak GBO increase appeared around 300 ms after stimulus onset, but its latency was shorter after S1 and longer after S2 under the 'with attention' than under the 'without attention' condition. This transient increase in the visual GBO is thought to reflect attention and to reset the activity of the visual system in preparation for a new stimulus.

Adult↗

PubMed1999

Event-related dynamics of the gamma-band oscillation in the human brain: information processing during a GO/NOGO hand movement task.

To investigate the gamma band activity relating to the discrimination process and motor behavior in the human brain, the event-related dynamics of the EEG spectrum was calculated during the visual GO/NOGO hand movement task and a control task (the visual element of the GO/NOGO task only) in eight subjects. The subjects were instructed to push (GO) or not to push (NOGO) a microswitch according to different visual stimuli and 21-channel scalp EEGs were recorded. The time courses of the power spectra after the stimuli were calculated using the fast Fourier transform for each condition (GO, NOGO and the control task), and were compared statistically between the conditions. The results suggested that a high gamma band oscillation, occurring at the frontal and left parieto-occipital areas at around 90 ms after the stimuli, relates to the discrimination process. Under the GO condition, this oscillation continued until 140 ms, and a subsequent oscillation occurred over the motor areas at around 200 ms, which seemed to be related to the motor action. On the other hand, under the NOGO condition, a low gamma band oscillation occurred in the central area at around 230 ms, which seemed to be related to the inhibition process.

Adult↗

PubMed1998

X-ray absorption of bromonaphthalene dissolved in supercritical fluid xenon.

The results of Br K-edge X-ray absorption measurements of 1-bromonaphthalene dissolved in supercritical fluid Xe are reported. As the pressure of Xe confined in a high-pressure cell is increased, the absorption spectrum of bromonaphthalene gradually appears, showing that Xe in the supercritical fluid state solvates the bromonaphthalene molecule. The spectrum of the dissolved sample shows a remarkable difference from that of the pure liquid sample in the near-edge region of the X-ray absorption spectrum, reflecting the interaction of the solute material with solvent Xe. Ab initio full multiple-scattering calculations can reproduce the spectral features qualitatively. A large value of the Debye-Waller factor must be introduced to give the best fit, corresponding to a large degree of spatial disorder and violent thermal vibration of the Xe atoms around the Br atom.

Journal Article↗

PubMed1998

Reconstruction of BL7B for UV, VIS and IR spectroscopy with a 3 m normal-incidence monochromator.

The beamline BL7B at the UVSOR facility for solid-state spectroscopy is currently under reconstruction. This reconstruction mainly involves the replacement of the 1 m Seya-Namioka-type monochromator (50-600 nm) with a 3 m NIM (modified version of McPherson model 2253), which covers the 50-1000 nm range with three gratings. The deviation angle of the gratings is 15 degrees. For linear and circular polarization experiments, the beamline optics consist of a two-grazing-incidence (87.5 degrees ) pre-mirror system and a normal-incidence (15 degrees ) post-mirror.

Journal Article↗

PubMed1998

Functional magnetic resonance imaging during recognition of written words: Chinese characters for concrete objects versus abstract concepts.

An attempt was made to apply functional magnetic resonance imaging (fMRI) to reveal cortical areas activated upon presentation of two groups of Chinese characters in six normal right-handed, male, Japanese subjects. Presentation of the characters representing 'abstract concepts' activated the bilateral occipital region without a significant difference between the bilateral occipital and temporal regions. Presentation of the characters representing 'concrete objects' resulted in significantly stronger activation in the left occipital and temporal regions. These results suggest that recognition of concrete characters involves a stronger initial process in the left occipital temporal cortices than recognition of abstract characters.

Adult↗

PubMed1998

Functional magnetic resonance imaging during recognition of written words: Chinese characters for concrete objects versus abstract concepts.

Adult↗

PubMed1998

The synchronization between brain areas under motor inhibition process in humans estimated by event-related EEG coherence.

To investigate the functional connection of brain areas under motor inhibition, the event-related coherence (ERCoh) of the electroencephalogram (EEG) was calculated for 10 subjects who were asked to perform a visual discrimination (GO/NO-GO) task. The subjects were instructed to push (GO) or not to push (NO-GO) a micro-switch according to different visual stimuli. Twenty-one-channel scalp EEGs were recorded and the surface Laplacians were calculated at F3, F4, C3, C4, P3 and P4 using the source derivation method. The time-courses of the inter- and intra-hemispheric coherence were calculated using the fast Fourier transform for each condition (GO or NO-GO), and were compared statistically between the two conditions. The results suggest that the ERCoh under the NO-GO condition consisted of two components; alpha band synchronization between bilateral frontal areas and theta band synchronization among bilateral frontal, central and parietal areas. It is likely that the former is related directly to the decision not to move, and the latter is related to the motor inhibition process.

Adult↗

PubMed1998

Hemispheric laterality in contextual recognition.

Hemispheric dominance in contextual recognition is now under discussion. Auditory event-related potentials (ERPs) with a contextual decision task were recorded to study hemispheric dominance by using the wave energy and amplitudes of N400 for eight native volunteers. Two types of 80 sentences with four clauses were used as the structure: [subject] + [object or complement] + [object] + [two-syllable verb]. One type was congruent and the other deviated at the terminal clause as an incongruent sentence. Twenty-one channel ERPs were triggered at the verbs and recorded during -200 and 1,000 ms, with a noncephalic reference from 0.05 to 30 Hz. The wave energy was calculated as mean square potentials and was normalized with the background activity (pretrigger 200 ms). The amplitudes of N400 showed significant differences between the incongruent and congruent sentences, but the hemispheric dominance for the amplitudes of N400 was not significant between the incongruent and congruent sentences. Reaction times with the index finger to respond to the deviated verbs were 470.0 (mean) +/- 42.5 (SD) ms. The maximum normalized wave energy within the mean reaction time showed significant differences between the incongruent and congruent sentences, and the left hemispheric energy was shown to be significantly higher than the right one.

Adult↗

PubMed1998

Differences in auditory scalp potentials evoked by meaningful words and nonlinguistic stimuli.

Differences in auditory evoked potentials with meaningful words and their reverse playback may reflect different neural processes in recognizing auditory stimuli. Auditory evoked potentials with the words and their reverse playback were analyzed for eight volunteers, and a maximal difference was observed at a latency around 400 msec. over the left middle temporal central area.

Cerebral Cortex↗

PubMed1997

The time course of interhemispheric EEG coherence during a GO/NO-GO task in humans.

Event-related coherence of the EEG was calculated for 10 subjects performing a visual discrimination GO/NO-GO task. The subjects were instructed to push (GO) or not to push (NO-GO) a button according to visual stimuli. Twenty-one-channel scalp EEGs were recorded and the surface Laplacian was calculated using the source derivation method. The time courses of the coherence between F3 and F4, C3 and C4, and P3 and P4 were calculated using the fast Fourier transform for each task and were compared between conditions. Statistical analysis showed that coherence in the NO-GO condition became significantly higher than that in the GO condition between F3 and F4. The synchronization between bilateral dorsolateral frontal areas might therefore play an important role in the motor inhibition process.

Adult↗

PubMed1997

Visual evoked potentials relating to imagery: words for concrete objects versus absolute concepts.

We recorded visual evoked potentials (VEPs) elicited with high or low imaginable Chinese characters (HIC or LIC), representing concrete objects or absolute concepts, respectively. A closed circle (CC) acts as control stimulus. These were displayed (at 1.6 degrees visual angle) for 35 ms on a TV monitor. Twenty-one channel VEPs (band-pas filter: 0.05-60 Hz), using balanced non-cephalic electrodes, were recorded from -100 to 924 ms for 11 right-handed male volunteers. The VEPs were analyzed by multivariate analysis of variance (MANOVA) and comparison of topographies at four remarkable peaks (P110, N160, P230 and N320). MANOVA showed significant differences (p < 0.001) for both conditions of channel and stimuli (HIC, LIC or CC). P100 for the CC-VEPs, N160 for the HIC- and LIC-VEPs, P230 for the CC-VEPs, and N320 for the HIC-VEPs were remarkable in the posterior scalp regions. Topographies at P100 and N160 showed no difference between the HIC- and LIC-stimuli. However, those at N320 showed difference between the HIC- and LIC-stimuli over the occipital and posterior temporal areas. Those results suggest that the responses at P100 and N160 might segregate Chinese characters from non Chinese characters. N320 suggested certain processes in imagery on recognizing Chinese characters over the occipital and posterior temporal areas.

Adult↗

PubMed1996

Visual evoked potentials to a faint light: signal propagation analyzed with peak latency and topographic mapping.

Accurate localization for the process of recognition of a light stimulus is yet to be determined. We studied 19-channel VEP from nine healthy volunteers, evoked by physiologically faint light less than 200 Cd/m2, using a light emitting diode (5 mm phi, 0.3 degrees, energized for 5 msec). VEP was bandpass filtered from 0.16 to 120 Hz, and analyzed from 20 msec pre-stimulus to 184.2 msec post-stimulus. The grand average VEP suggested an initial positive peak at 115.8 msec at the frontal poles and at 136 msec over the occipital areas. An initial negative peak was noted at 156 msec at the frontal poles and at 179.2 msec over the occipital areas. This might suggest that the potentials evoked had propagated from the frontal poles to the occipital areas, taking about 20 msec. However, the topographic maps contained little evidence for such a propagation, but rather indicated the waxing and waning of positive or negative extremes.

Adult↗