Biomedical subjects

Satoru Miyauchi

Publications and source records attributed to Satoru Miyauchi.

18 recordsLinked to original sources

PubMed2005

Application of artificial neural network to fMRI regression analysis.

We used an artificial neural network (ANN) to detect correlations between event sequences and fMRI (functional magnetic resonance imaging) signals. The layered feed-forward neural network, given a series of events as inputs and the fMRI signal as a supervised signal, performed a non-linear regression analysis. This type of ANN is capable of approximating any continuous function, and thus this analysis method can detect any fMRI signals that correlated with corresponding events. Because of the flexible nature of ANNs, fitting to autocorrelation noise is a problem in fMRI analyses. We avoided this problem by using cross-validation and an early stopping procedure. The results showed that the ANN could detect various responses with different time courses. The simulation analysis also indicated an additional advantage of ANN over non-parametric methods in detecting parametrically modulated responses, i.e., it can detect various types of parametric modulations without a priori assumptions. The ANN regression analysis is therefore beneficial for exploratory fMRI analyses in detecting continuous changes in responses modulated by changes in input values.

Adult↗

PubMed2005

Maintaining coherence of dynamic objects requires coordination of neural systems extended from anterior frontal to posterior parietal brain cortices.

Object representation in visual working memory enables humans to perceive a consistent visual world and must satisfy two attributes: coherence and dynamic updating. The present study measured brain activity using functional magnetic resonance imaging (fMRI) during the multiple object permanence tracking (MOPT) task, which requires observers to process simultaneously both coherence maintenance and dynamic updating of objects. Whole brain analysis revealed anterior and ventral parts of frontal area and dorsal frontoparietal activation during both object-moving and object-stationary conditions. Subsequent region-of-interest analyses in the anterior/ventral frontal and the dorsal frontoparietal regions revealed that these two systems engage the two different cognitive processes involved in the MOPT task, with coherency maintenance processed in the anterior/ventral frontal areas and spatial processing in the dorsal frontoparietal network. These results suggest that cooperation between these two systems underpins object representations in visual working memory.

Frontal Lobe↗

PubMed2004

The sensorimotor transformation of cross-modal spatial information in the anterior intraparietal sulcus as revealed by functional MRI.

The parietal cortex in monkeys and humans has been shown to play an important role in the transformation of sensory information to motor commands. However, it is still unclear whether in humans, these areas are divided functionally into subregions based on different combinations of sensory and motor modalities. To identify subregions in the parietal cortex involved in the sensorimotor information transformation between different modalities, functional MRI was used to examine brain areas activated during tasks requiring different sensorimotor transformations--i.e., various combinations of eye (saccade) or finger movements triggered by visual or somatosensory cues. We then compared the activations between cross-modal conditions (eye movements triggered by somatosensory cues and finger movements triggered by visual cues) and intramodal (eye movements triggered by visual cues and finger movements triggered by somatosensory cues) conditions. Although the parietal cortex was involved in all tasks regardless of sensorimotor combinations, the only region activated to a greater degree in the cross-modal conditions compared to the intramodal conditions was the anterior portion of the intraparietal sulcus (a-IPS). The results suggest that the a-IPS plays an important role in the sensorimotor transformation of cross-modal spatial information.

Adult↗

PubMed2004

Neural mechanisms of spatial stimulus-response compatibility: the effect of crossed-hand position.

Previous psychological experiments have indicated the existence of a visual-proprioceptive interaction in spatial stimulus-response compatibility (SSRC) tasks, but there is little specific information on the neural basis of such interaction in humans. Using functional magnetic resonance imaging (fMRI), we compared the neural activity associated with two different aspects of spatial coding: the coding of the "internal" spatial position of motor-response effectors (i.e., the position of body parts) as obtained through proprioception, and the coding of "external" positions, i.e., the positions of visual stimuli. A 2 x 2 factorial design was used to investigate the spatial compatibility (incompatible versus compatible) between a visual stimulus and hand position (crossed versus uncrossed). The subjects were instructed to respond to stimuli presented to the right or left visual field with either the ipsilateral (compatible condition) or the contralateral hand (incompatible condition). The incompatible condition produced stronger activation in the bilateral superior parietal lobule, inferior parietal lobule, and bilateral superior frontal gyrus than the compatible condition. The crossed-hand condition produced stronger activation in the bilateral precentral gyrus, superior frontal gyrus, superior parietal lobule, and superior temporal gyrus than the uncrossed-hand condition. These results suggest that activity in the frontal-parietal regions is related to two functions: (1) representation of the visual stimulus-motor response spatial configuration in an SSRC task, and (2) integration between external visual and internal proprioceptive sensory information. The activation in the superior temporal gyrus was not affected by the visual stimulus-motor response spatial configuration in an SSRC task; rather, it was affected by the crossed-hand posture. Thus, it seems to be related to representing internal proprioceptive sensory information necessary to carry out motor actions.

Adult↗

PubMed2004

Circulatory basis of fMRI signals: relationship between changes in the hemodynamic parameters and BOLD signal intensity.

Blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) is widely used as a tool for functional brain mapping. During brain activation, increases in the regional blood flow lead to an increase in blood oxygenation and a decrease in paramagnetic deoxygenated hemoglobin (deoxy-Hb), causing an increase in the MR signal intensity at the site of brain activation. However, not a few studies using fMRI have failed to detect activation of areas that ought to have been activated. We assigned BOLD-positive (an increase in the signal intensity), BOLD-negative (a decrease in the signal intensity), and BOLD-silent (no change) brain activation to respective circulatory conditions through a description of fMRI signals as a function of the concentration of oxygenated Hb (oxy-Hb) and deoxy-Hb obtained with near-infrared optical imaging (NIOI). Using this model, we explain the sensory motor paradox in terms of BOLD-positive, BOLD-negative, and BOLD-silent brain activation.

Adult↗

PubMed2004

Asymmetric activation to the context-dependent right in the right inferior frontal region.

In human spatial recognition, right and left are not recognized symmetrically. Although there have been many studies on the hemispheric asymmetry of the human brain, asymmetries in high-level recognition (such as independence from input or output hemisphere) have not been studied extensively. We found that the human brain recognizes right and left asymmetrically in high-level recognition. Experiments were performed in which participants crossed their hands and were required to judge the side of a tactile stimulus on the index finger in two different contexts: 'which hand was touched' or 'on which side of the space the touched hand was located'. The right inferior frontal region was significantly more activated by the 'contextually defined right' stimulus (right-hand stimulation in the 'which hand' context and right-space stimulation in the 'which space' context) than by the 'contextually defined left' stimulus. However, no activation that was more activated by the 'contextually defined left' than by the 'contextually defined right' was found. This asymmetric activation suggests that 'right' is the more outstanding side for human spatial recognition.

Adult↗

PubMed2003

Discrete stochastic process underlying perceptual rivalry.

In perceptual rivalry such as ambiguous figure perception and binocular rivalry, the conscious percept spontaneously alternates between two stable interpretations of an unchanging stimulus. It is well known that the time intervals of the perceptual alternation follow a gamma distribution (GD), but its implication for the alternation mechanism has not been clarified. We examined quantitatively GDs fitted to alternation intervals, and found that the shape-determining parameter alpha of the GDs took natural numbers. Because a GD determined by a natural number alpha is mathematically obtained from a discrete stochastic process (Poisson process), our result indicates that such a stochastic process underlies perceptual rivalry and that the alpha-time accumulation of the discrete events causes a perceptual alternation.

Adult↗

PubMed2003

Modular organization of internal models of tools in the human cerebellum.

Human capabilities in manipulating many different tools with dexterity suggest modular neural organization at functional levels, but anatomical modularity underlying the capabilities has yet to be demonstrated. Although modularity in phylogenetically older parts of the cerebellum is well known, comparable modularity in the lateral cerebellum for cognitive functions remains unknown. We investigated these issues by functional MRI (fMRI) based on our previous findings of a cerebellar internal model of a tool. After subjects intensively learned to manipulate two novel tools (the rotated mouse whose cursor appeared at a rotated position, and the velocity mouse whose cursor velocity was proportional to the mouse position), they could easily switch between the two. The lateral and posterior cerebellar activities for the two different tools were spatially segregated, and their overlaps were <10%, even at low statistical thresholds. Activities of the rotated mouse were more anterior and lateral than the velocity mouse activities. These results were consistent with predictions by the MOdular Selection And Identification Controller (MOSAIC) model that multiple internal models compete to partition sensory-motor experiences and their outputs are linearly combined for a particular context.

Adult↗

PubMed2003

Synthesis and structure-activity relationships of 5-amino-6-fluoro-1-[(1R,2S)-2-fluorocyclopropan-1-yl]-8-methylquinolonecarboxylic acid antibacterials having fluorinated 7-[(3R)-3-(1-aminocyclopropan-1-yl)pyrrolidin-1-yl] substituents.

A series of novel 5-amino-6-fluoro-1-[(1R,2S)-2-fluorocyclopropan-1-yl]-8-methylquinolones bearing fluorinated (3R)-3-(1-aminocyclopropan-1-yl)pyrrolidin-1-yl substituents at the C-7 position (2-4) was synthesized to obtain potent drugs for infections caused by Gram-positive pathogens, which include resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae (PRSP), and vancomycin-resistant enterococci (VRE). These fluorinated compounds 2-4 exhibited potent antibacterial activity comparable with that of a compound bearing a non-fluorinated (3R)-3-(1-aminocyclopropan-1-yl)pyrrolidine moiety at the C-7 position (1) and had at least 4 times more potent activity against representative Gram-positive bacteria than ciprofloxacin (CPFX), gatifloxacin (GFLX), or moxifloxacin (MFLX). Among them, the 7-[(3S,4R)-4-(1-aminocyclopropan-1-yl)-3-fluoropyrrolidin-1-yl] derivative 3 (=DQ-113), which showed favorable profiles in preliminary toxicological and nonclinical pharmcokinetic studies, exhibited potent antibacterial activity against clinically isolated resistant Gram-positive pathogens.

Anti-Bacterial Agents↗

PubMed2003

Internal forward models in the cerebellum: fMRI study on grip force and load force coupling.

Internal models are neural mechanisms that can mimic the input-output or output-input properties of the motor apparatus and external objects. Forward internal models predict sensory consequences from efference copies of motor commands. There is growing acceptance of the idea that forward models are important in sensorimotor integration as well as in higher cognitive function, but their anatomical loci and neural mechanisms are still largely unknown. Some of the most convincing evidence that the central nervous system (CNS) makes use of forward models in sensory motor control comes from studies on grip force-load force coupling. We first present a brief review of recent computational and behavioral studies that provide decisive evidence for the utilization of forward models in grip force-load force coupling tasks. Then, we used functional magnetic resonance imaging (fMRI) to measure the brain activity related to this coupling and demonstrate that the cerebellum is the most likely site for forward models to be stored.

Adult↗

PubMed2003

Information flow related to visual search assessed using magnetoencephalography.

The sequence of neural activation during a visual search task was investigated using magnetoencephalography and the source locations for the activations were analyzed using a single-dipole algorithm. Five components (M1-5) were detected at mean latencies of 110, 146, 196, 250 and 333 ms in both of two different stimulus conditions; a target popped out in one stimulus condition (pop-out), while it did not in the other condition (non-pop-out). Statistical analysis showed that the M3 amplitude was larger and the M5 latency was shorter in the pop-out condition than in the non-pop-out condition, while there was no difference in the other components between the conditions. Neural sources were localized in the calcarine sulcus (M1) and the posterior fusiform gyrus (M2) of the hemisphere contralateral to the stimuli, the intraparietal sulcus and the posterior superior temporal sulcus (M3) in either of the hemispheres, and the calcarine sulcus (M4) of the same hemisphere in which the early processing (M1 and M2) occurred. The criteria for source localization were not satisfied for M5. The results suggest that the processing for pop-out and non-pop-out stimuli share a common mechanism; after early feature processing in the occipital cortex (M1 and M2), visual information is processed in the parietal and temporal regions (M3) and then some of this information is fed back to the occipital cortex (M4).

Adult↗

PubMed2003

Attentional set for external information activates the right intraparietal area.

Visual attention can be allocated to a location or an object by using two different types of information: internal information and external information. The results of recent psychological studies [Bagon and Egeth, Percept. Psychophys. 55 (1994) 485] suggest that an observer's attentional set determines how these two kinds of information are used in visual tasks. In this study, we measured brain activities during two modes of visual search; one is the feature search mode, in which an attentional set for knowledge of a target item (internal information) is used, and the other is the singleton detection mode, in which an attentional set for oddness in the visual scene (external information) is used. We found extended activation in the frontal and parietal areas for both search modes. In addition, a direct comparison of brain activity during the singleton detection mode and the feature search mode revealed that the areas around the right intraparietal sulcus were more involved in the attentional set for oddness. These results suggest that the human right intraparietal cortex is related to the attentional set for external information.

Adult↗

PubMed2003

Functional MRI of brain activation evoked by intentional eye blinking.

Eye blinking is not only a reflexive action to protect the ocular surface from injury and desiccation; it can also be done intentionally. However, only a few studies have investigated the brain mechanism controlling intentional blinking, and there are still inconsistencies among the reported activation patterns in the human brain evoked by intentional blinking. In monkeys, some areas where blinking is evoked by electrical microstimulation have been found in the premotor areas and in the posterior parietal cortex. But there have been no reports about neuronal activity related to blinking in the cerebral cortex. In the present study, the brain activation evoked by intentional blinking was examined in humans by using fMRI, and the activations were found in the middle precentral gyrus, but not in the posterior parietal cortex, suggesting that the premotor areas, rather than the posterior parietal cortex, are important for controlling intentional blinking.

Adult↗

PubMed2003

Human precentral cortical activation patterns during saccade tasks: an fMRI comparison with activation during intentional eyeblink tasks.

Some fMRI studies in humans have located the frontal eye field (FEF) in two distinct regions along the precentral sulcus (PCS): one localized more medically, in the superior precentral sulcus (supPCR) at the junction with the superior frontal sulcus, and the other localized more laterally, along the medial part of the inferior precentral sulcus (infPCR). However, there has been no evidence of any different task activations between the regions. In the present study using fMRI, we have compared activation patterns in the regions near the PCS during saccade, fixation, and eyeblink tasks. We found that only the supPCR was activated specifically by the saccade task, while the infPCR was activated by both the saccade and eyeblink tasks. This result provides evidence that the supPCR is the human FEF homologous to the monkey FEF and that the infPCR may be homologous to the monkey premotor area.

Adult↗

PubMed2002

Dorsal visual cortex activity elicited by posture change in a visuo-tactile matching task.

To investigate the process of crossmodal spatial recognition, we examined the effect of posture change on the recognition of a tactile stimulus position. The task was to judge whether a visual and a tactile stimulus, presented to the left or right, were on the same or different sides while subjects crossed or uncrossed their hands. Under a condition which removed the effect of response bias to the left and right, the dorsal visual cortex (area 18/19) and the precuneus were more activated in the crossed hands condition. The dorsal visual cortex activation suggests that the activity of brain areas classically considered to be visual cortex is affected by posture change, and reflects the reciprocal process across different modalities in spatial recognition.

Adult↗

PubMed2002

An fMRI-constrained MEG source analysis with procedures for dividing and grouping activation.

To analyze neural activity using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI), we developed a method for fixing equivalent current dipoles of MEG in activation areas of fMRI. It includes a procedure for dividing large fMRI activation volumes into subvolumes in each of which a dipole is placed and another procedure for grouping neighboring dipoles whose temporal changes are inseparable based on MEG data. To optimize the procedures' parameters, we carried out simulations and found that (1) any single dipole within 10 mm from a true source can explain MEG data with a correlation of 94% on average for the low signal-to-noise ratio of 3 and (2) a neighboring dipole within a few tens of millimeters from the dipole nearest to the true source tends to be highly incorporated in explaining MEG data. We applied the method to data measured in a language experiment and detected 13 significant sources. The results show that the present method is promising for detecting neural activity originating from a number of separate neural sources.

Algorithms↗

PubMed2002

[Functional MRI activation in area V4 alpha during a hue arrangement test].

BACKGROUND: Recent studies of cerebral information processing have shown that area V4 alpha, the area anterior to area V4, which is known as the human color center, is also associated with color. However, our clinical study has shown that lesions associated with hue arrangement test failures are more anterior than those associated with pseudoisochromatic plate test failure. PURPOSE AND METHODS: We studied area V4 alpha, and planned two functional magnetic resonance experiments for V4 alpha activity during the hue arrangement test. The task in the first experiment was virtual simulation of the hue arrangement test. The second experiment involved a task more specific to color information processing. RESULTS: We found significant activity in area V4 alpha in healthy subjects. CONCLUSIONS: We have reported that one of our patients with a more anterior lesion excluding area V4 had dyschromatopsia, as revealed by a panel D-15 test. Our experimental data and the clinical findings suggest that area V4 alpha plays an important role in processing during the hue arrangement test.

Cerebral Cortex↗

PubMedDate not supplied

Adaptation to left-right reversed vision rapidly activates ipsilateral visual cortex in humans.

The brain mechanisms of adaptation to visual transposition are of increasing interest, not only for research on sensory-motor coordination, but also for neuropsychological rehabilitation. Sugita [Nature 380 (1996) 523] found that after adaptation to left-right reversed vision for one and a half months, monkey V1 neurons responded to stimuli presented not only in the contralateral visual field, but also in the ipsilateral visual field. To identify the underlying neuronal mechanisms of adaptation to visual transposition, we conducted fMRI and behavioral experiments for which four adult human subjects wore left-right reversing goggles for 35/39 days, and investigated: (1) whether ipsilateral V1 activation can be induced in human adult subjects; (2) if yes, when the ipsilateral activity starts, and what kind of behavioral/psychological changes occur accompanying the ipsilateral activity; (3) whether other visual cortices also show an ipsilateral activity change. The results of behavioral experiments showed that visuomotor coordinative function and internal representation of peripersonal space rapidly adapted to the left-right reversed vision within the first or second week. Accompanying these behavioral changes, we found that both primary (V1) and extrastriate (MT/MST) visual cortex in human adults responded to visual stimuli presented in the ipsilateral visual field. In addition, the ipsilateral activity started much sooner than the one and a half months, which had been expected from the monkey neurophysiological study. The results of the present study serve as physiological evidence of large-scale, cross-hemisphere, cerebral plasticity that exists even in adult human brain.

Adaptation, Physiological↗