Biomedical subjects

Maki Suzuki

Publications and source records attributed to Maki Suzuki.

15 recordsLinked to original sources

PubMed2006

Reactivation of medial temporal lobe and occipital lobe during the retrieval of color information: A positron emission tomography study.

It is widely accepted that memory traces of an event include various types of information about the content of the event and about the circumstances in which the individual experienced it. However, how these various types of information are stored and later retrieved is poorly understood. One hypothesis postulates that the retrieval of specific event information reactivates regions that were active during the encoding of this information, with the aid of binding functions of the medial temporal lobe (MTL) structures. We used positron emission tomography to identify the brain regions related to the encoding and retrieval of color information. Specifically, we assessed whether overlapping activity was found in both the MTL structures and color-related cortical regions during the encoding and retrieval of color information attached with meaningless shapes. During the study, subjects were asked to encode colored (red or green) and achromatic random shapes. At subsequent testing, subjects were presented with only achromatic shapes, which had been presented with or without colors during encoding, and were engaged in retrieval tasks of shapes and colors. Overlapping activity was found in the MTL and occipital lobe (the lingual and inferior occipital gyri) in the right hemisphere during the encoding and retrieval of meaningless shapes with color information compared with those without color information. Although there are some limitations to be considered, the present findings seem to support the view that the retrieval of specific event information is associated with reactivation of both the MTL structures and the regions involved during encoding of the information.

Adult↗

PubMed2006

Comparison of the physiology, morphology, and leaf demography of tropical saplings with different crown shapes.

Branch architecture, leaf photosynthetic traits, and leaf demography were investigated in saplings of two woody species, Homolanthus caloneurus and Macaranga rostulata, co-occurring in the understory of a tropical mountain forest. M. rostulata saplings have cylindrical crowns, whereas H. caloneurus saplings have flat crowns. Saplings of the two species were found not to differ in area-based photosynthetic traits and in average light conditions in the understory of the studied site, but they do differ in internode length, leaf emergence rate, leaf lifespan, and total leaf area. Displayed leaf area of H. caloneurus saplings, which have the more rapid leaf emergence, was smaller than that of M. rostulata saplings, which have a longer leaf lifespan and larger total leaf area, although M. rostulata saplings showed a higher degree of leaf overlap. Short leaf lifespan and consequent small total leaf area would be linked to leaf overlap avoidance in the densely packed flat H. caloneurus crown. In contrast, M. rostulata saplings maintained a large total leaf area by producing leaves with a long leaf lifespan. In these understory saplings with a different crown architecture, we observed two contrasting adaptation strategies to shade which are achieved by adjusting a suite of morphological and leaf demographic characters. Each understory species has a suite of morphological traits and leaf demography specific to its architecture, thus attaining leaf overlap avoidance or large total leaf area.

Euphorbiaceae↗

PubMed2005

Dissociable roles of prefrontal and anterior cingulate cortices in deception.

Recent neuroimaging studies have shown the importance of the prefrontal and anterior cingulate cortices in deception. However, little is known about the role of each of these regions during deception. Using positron emission tomography (PET), we measured brain activation while participants told truths or lies about two types of real-world events: experienced and unexperienced. The imaging data revealed that activity of the dorsolateral, ventrolateral and medial prefrontal cortices was commonly associated with both types of deception (pretending to know and pretending not to know), whereas activity of the anterior cingulate cortex (ACC) was only associated with pretending not to know. Regional cerebral blood flow (rCBF) increase in the ACC was positively correlated with that in the dorsolateral prefrontal cortex only during pretending not to know. These results suggest that the lateral and medial prefrontal cortices have general roles in deception, whereas the ACC contributes specifically to pretending not to know.

Adolescent↗

PubMed2005

Recruitment of fusiform face area associated with listening to degraded speech sounds in auditory-visual speech perception: a PET study.

For the fast and accurate cognition of external information, the human brain seems to integrate information from multi-sensory modalities. We used positron emission tomography (PET) to identify the brain areas related to auditory-visual speech perception. We measured the regional cerebral blood flow (rCBF) of young, normal volunteers during the presentation of dynamic facial movement at vocalization and during a visual control condition (visual noise), both under the two different auditory conditions of normal and degraded speech sounds. The subjects were instructed to listen carefully to the presented speech sound while keeping their eyes open and to say what they heard. The PET data showed that elevation of rCBF in the right fusiform gyrus (known as the "face area") was not significant when the subjects listened to normal speech sound accompanied by a dynamic image of the speaker's face, but was significant when degraded speech sound (filtered with a 500 Hz low-pass filter) was presented with the facial image. The results of the present study confirm the possible involvement of the fusiform face area (FFA) in auditory-visual speech perception, especially when auditory information is degraded, and suggest that visual information is interactively recruited to make up for insufficient auditory information.

Acoustic Stimulation↗

PubMed2005

Dissociable brain activations during the retrieval of different kinds of spatial context memory.

Although memory for spatial information has often been regarded as unitary, it may be divided into two distinct types: memory for the place where an individual experienced an event and memory for the location of an experienced event within a specific reference object. We used functional magnetic resonance imaging (fMRI) to elucidate the distinctions between the retrieval of these two types of spatial context memory. During scanning, subjects judged the room (Place task) in which a photograph had been presented or the location of the photograph on the computer display (R-L task) during the encoding phase. In a control task, subjects were asked to judge whether the photograph had been presented or not. The left middle frontal gyrus, lateral parietal and occipital regions, and bilateral precunei were found to be active during both the Place task and the R-L task compared with the control task. Critically, the place task, compared with the R-L task, was associated with activations in the right lateral prefrontal gyri, the posterior part of the left parahippocampal gyrus, bilateral retrosplenial and lateral parieto-occipital areas, whereas the R-L task, relative to the place task, with activation only in the right lateral parietal cortex. These findings indicate that the retrieval processes of spatial context memory are not associated with a single network, but may vary and recruit different neural networks depending on the type of spatial information to be retrieved.

Adult↗

PubMed2004

Changes in brain activation associated with use of a memory strategy: a functional MRI study.

It has been confirmed that some kinds of what are called memory strategies dramatically improve the performance of memory recall. However, there has been no direct research to examine changes in brain activity associated with the use of the method of loci within individuals. In the present study, using fMRI, we compared brain activations before and after instruction in the method of loci during both the encoding and recall phases. The resulting behavioral data showed that the use of the method of loci significantly increased scores for memory recall. The imaging data showed that encoding after instruction in the method of loci, relative to encoding before it, was associated with signal increases in the right inferior frontal gyrus, bilateral middle frontal gyrus, left fusiform gyrus, and bilateral lingual gyrus/posterior cingulate gyrus. Comparison of recall after instruction in the method of loci with that before it showed significant activation in the left parahippocampal gyrus/retrosplenial cortex/cingulate gyrus/lingual gyrus, left precuneus, left fusiform gyrus, and right lingual gyrus/cingulate gyrus. The present study demonstrated the changes in brain activation pattern associated with the use of the method of loci; left fusiform and lingual activity was associated with both the encoding and recall phases, bilateral prefrontal activity with the encoding phase, and activity of the posterior part of the parahippocampal gyrus, retrosplenial cortex, and precuneus with the recall phase. These findings suggest that brain networks mediating episodic encoding and retrieval vary with how individuals encode the same stimuli.

Adult↗

PubMed2004

Neural correlates of context memory with real-world events.

There has been little evidence for the difference in the retrieval processes of when and where something happened, one of the important factors in understanding episodic memory. We used positron emission tomography (PET) to identify the neural networks associated with temporal and spatial context memory of events experienced under experimental conditions similar to those of everyday life. Before PET, subjects experienced 36 events. The events were divided into four groups of nine each. The subjects experienced the first two groups of events before a 15-min recess and the other two after the recess; they experienced the first and last groups of events in one room, took a recess in another room, and experienced the second and third groups in a different room. During PET, the subjects were scanned under three different retrieval tasks: a time-retrieval task, a place-retrieval task, and a simple recognition task. The results showed that the retrieval of time and space, compared with the simple recognition, was associated with activity in substantially different regions as well as a common region: time retrieval with the posterior part of the right orbitofrontal cortex and left inferior parietal lobule, place retrieval with two regions in right parietal association cortex, right posterior cingulate gyrus, left precentral gyrus, and right cerebellum, and both with the right inferior frontal gyrus. These findings indicate that there are unique areas, in addition to a common area, for retrieving temporal and spatial context.

Adult↗

PubMed2004

Phospholipase C involvement in activation of the muscarinic receptor-operated cationic current in Guinea pig ileal smooth muscle cells.

In guinea pig single ileal smooth muscle cells held under voltage-clamp, the role of phospholipase C (PLC) in activation of the muscarinic receptor-operated cationic current (I(cat)) was studied. U73122, a PLC inhibitor, prevented the generation of I(cat) by the muscarinic agonist carbachol. The effect did not involve muscarinic receptor block since it also blocked I(cat) which was evoked by GTPgammaS applied intracellularly to activate G proteins bypassing muscarinic receptors. Also, neither cationic channel block nor other possible nonspecific actions seemed to be involved since its analogue (U73343), structurally close but deficient of the PLC-inhibiting activity, did not significantly affect carbachol- or GTPgammaS-evoked I(cat). Antibodies against the alpha subunits of G(q)/G(11) proteins (Galpha(q)/Galpha(11)-antibody) blocked only the small component of carbachol-evoked I(cat), which was associated with an increase in [Ca(2+)](i) linked to an increase in G(q/11) protein-regulated PLC activity. 1-Oleoyl-2-acetyl-sn-glycerol (OAG), an analogue of diacylglycerol (DAG) produced via PLC-catalyzed metabolism, produced no or only a small current by itself, with the carbachol-evoked I(cat) remaining unchanged. These results provide evidence for the importance of PLC in I(cat) generation, and they also strongly suggest that the activity of PLC involved in the primary activation of I(cat) is neither under regulation by G(q/11) proteins nor dependent on the action of DAG.

Animals↗

PubMed2003

Size structure of current-year shoots in mature crowns.

Characteristics of current-year shoot populations were examined for three mature trees of each of three deciduous broad-leaved species. For first-order branches (branches emerging from the vertical trunk) of the trees examined, lengths or diameters of all current-year shoots were measured. Total leaf mass and total current-year stem mass of first-order branches were estimated using an allometric relationship between leaf or stem mass and length or diameter of current-year stems. For each tree, the number of current-year shoots on a first-order branch was proportional to the basal stem cross-sectional area of the branch. On the other hand, first-order branches had shoot populations with size structures similar to each other. As a result, the leaf mass of a first-order branch was proportional to the basal stem cross-sectional area of the branch, being compatible with the pipe-model relationship. All current-year shoot populations had positively skewed size structures. Because small shoots have a larger ratio of leaf mass to stem mass than large shoots, first-order branches had an extremely large ratio of leaf mass to current-year stem mass. This biased mass allocation will reduce costs for current stem production, respiration and future radial growth, and is beneficial to mature trees with a huge accumulation of non- photosynthetic organs. The allometric relationships between leaf mass and basal stem diameter and that between leaf mass and current-year stem mass of first-order branches were each similar across the trees examined. Characteristics of shoot populations tended to offset inter-species diversity of shoot allometry so that branch allometry shows inter-species convergence.

Acer↗

PubMed2003

Changes in brain activation patterns associated with learning of Korean words by Japanese: an fMRI study.

We used functional magnetic resonance imaging (fMRI) to explore the change in brain activation associated with the learning of Korean words written in Han-gul characters (K-words) by young Japanese at two stages. Subjects were 12 right-handed native Japanese without previous knowledge of Korean words and characters. On the first day they were taught the pronunciation and meaning of 20 K-words. Then, after the first fMRI session (on day 2), they were given a set of 20 cards with the words and corresponding photographs. They also received a tape and were instructed to memorize the 20 K-words by studying them every day until the day of the second fMRI session (day 16). During the fMRI sessions, 20 Japanese words written in kana syllabograms (J-words) and the 20 previously presented K-words, as well as 20 new K-words (Kn-words) were presented visually for silent reading. The first J-word reading, relative to the first K-word reading, showed activation in the left angular gyrus. K-word reading relative to J-word reading during both sessions showed activation in occipital regions. Within these activated areas, session by condition interaction was found only in the left angular gyrus. The interaction between session and condition resulted from the fact that the differences in blood oxygenation-level-dependent signals between K-words and J-words and between Kn-words and J-words were significantly greater in the first session than in the second session. From the results, we concluded that patterns of brain activation changed as the memory of the 20 K-words became fixed through daily practice and that reading of both Korean words and Japanese syllabograms engaged the left angular gyrus.

Adult↗

PubMed2002

Neural basis of temporal context memory: a functional MRI study.

Temporal context information is crucial to understanding human episodic memory. Human lesion and neuroimaging data indicate that prefrontal regions are important for retrieving temporal context memory, although the exact nature of their involvement is still unclear. We employed functional magnetic resonance imaging (fMRI) to elucidate the neural basis of two kinds of temporal context memory: the temporal order of items between lists and within a list. On the day of the fMRI experiment, subjects memorized a list of 30 pictures in the morning and another list of 30 pictures in the afternoon. During the scanning session, the subjects performed three tasks. In a between-lists task, they were asked to judge the temporal order between two items that had been presented in different lists. In a within-list task, they were asked to judge the temporal order between two items that had been presented in a single list. We found bilateral prefrontal activities during these two temporal context memory tasks compared with a simple item-recognition task. Furthermore, in direct comparison between these two tasks, we found differential prefrontal activities. Thus, right prefrontal activity was associated with temporal order judgment of items between lists, whereas left prefrontal activity was related to temporal order judgment of items within a list. These results indicate that retrieval processes of two kinds of temporal context memory are supported by different, but overlapping, sets of cerebral regions. We speculate that this reflects different cognitive processes for retrieving temporal context memory between separate episodes and within a single episode.

Adult↗

PubMed2002

Encoding-related brain activity during deep processing of verbal materials: a PET study.

The recent advent of neuroimaging techniques provides an opportunity to examine brain regions related to a specific memory process such as episodic memory encoding. There is, however, a possibility that areas active during an assumed episodic memory encoding task, compared with a control task, involve not only areas directly relevant to episodic memory encoding processes but also areas associated with other cognitive processes for on-line information. We used positron emission tomography (PET) to differentiate these two kinds of regions. Normal volunteers were engaged in deep (semantic) or shallow (phonological) processing of new or repeated words during PET. Results showed that deep processing, compared with shallow processing, resulted in significantly better recognition performance and that this effect was associated with activation of various brain areas. Further analyses revealed that there were regions directly relevant to episodic memory encoding in the anterior part of the parahippocampal gyrus, inferior frontal gyrus, supramarginal gyrus, anterior cingulate gyrus, and medial frontal lobe in the left hemisphere. Our results demonstrated that several regions, including the medial temporal lobe, play a role in episodic memory encoding.

Adult↗

PubMed2002

MBLR, a new RING finger protein resembling mammalian Polycomb gene products, is regulated by cell cycle-dependent phosphorylation.

BACKGROUND: The RING finger proteins function in a variety of fundamental cellular processes. The products of some members of the Polycomb group (PcG) bear ring finger domains and are defined as a subclass of RING finger proteins. Among them are Drosophila posterior sex combs and suppressor 2 of zeste, whose RING fingers are conserved in vertebrate PcG proteins Mel18 and Bmi1. RESULTS: We have identified a new mammalian RING finger protein, termed MBLR due to its structural similarity to Mel18 and Bmi1 (Mel18 and Bmi1-like RING finger protein). MBLR interacts with some PcG proteins: in vitro biochemical data support the idea of a direct interaction of MBLR's RING finger domain with Ring1B, which is highly homologous to one of the mammalian PcG genes, Ring1A. We also show that MBLR acts as a transcriptional repressor in transiently transfected cells, as is the case for other PcG proteins. Immunocytochemical analysis reveals that MBLR protein is localized in a fine-grained distribution throughout the nucleoplasm in interphase cultured cells and in a fainter diffuse cytoplasmic distribution in mitotic cells. In addition, we find that serine 32 of MBLR is specifically phosphorylated during mitosis, most likely by CDK7, a component of the basal transcriptional machinery. CONCLUSION: Similarities to previously defined PcG proteins suggest that MBLR should be included in the same subclass of RING finger proteins as Mel18 and Bmi1. Although the biological relevance of the cell cycle-related phosphorylation remains to be demonstrated, serine 32 phosphorylation could nevertheless be functionally important.

Amino Acid Sequence↗

PubMed2002

Involvement of the Polycomb-group gene Ring1B in the specification of the anterior-posterior axis in mice.

The products of the Polycomb group of genes form complexes that maintain the state of transcriptional repression of several genes with relevance to development and in cell proliferation. We have identified Ring1B, the product of the Ring1B gene (Rnf2 - Mouse Genome Informatics), by means of its interaction with the Polycomb group protein Mel18. We describe biochemical and genetic studies directed to understand the biological role of Ring1B. Immunoprecipitation studies indicate that Ring1B form part of protein complexes containing the products of other Polycomb group genes, such as Rae28/Mph1 and M33, and that this complexes associate to chromosomal DNA. We have generated a mouse line bearing a hypomorphic Ring1B allele, which shows posterior homeotic transformations of the axial skeleton and a mild derepression of some Hox genes (Hoxb4, Hoxb6 and Hoxb8) in cells anterior to their normal boundaries of expression in the mesodermal compartment. By contrast, the overexpression of Ring1B in chick embryos results in the repression of Hoxb9 expression in the neural tube. These results, together with the genetic interactions observed in compound Ring1B/Mel18 mutant mice, are consistent with a role for Ring1B in the regulation of Hox gene expression by Polycomb group complexes.

Alleles↗

PubMed2000

Allometric differences between current-year shoots and large branches of deciduous broad-leaved tree species.

Current-year shoots are mostly made of primary tissues, whereas first-order branches comprise mainly secondary tissues. Differences in tissue composition of these units reflect differences in functional design. We compared the allometry of current-year shoots and first-order branches in eight deciduous broad-leaved tree species and examined the functional differences underlying the design of current-year shoots and first-order branches. Allometric relationships of first-order branches tended to be compatible with predictions of the pipe model and elastic similarity model. That is, allometric constants of the relationships between leaf mass and stem diameter at the branch base and between stem diameter and stem mass were 2.0 and 0.33-0.38, respectively, indicating that the functional regulation of stem form of first-order branches can be predicted by the two models. However, allometric relationships of current-year shoots were not compatible with the predictions of the pipe and elastic similarity models. Thus, the allometric constant of the relationship between leaf mass and stem diameter at the base of current-year shoots was larger than 2.0, and the allometric constant of the relationship between stem length and stem diameter of shoots was larger than 1.0 in all species examined. However, current-year shoots had an allometric constant of leaf mass against stem length that was less than 1.0, suggesting a functional demand on shoot design to reduce self-shading. Also, allometric constants of stem length against stem diameter at the shoot base were larger in monopodial species than in sympodial species, whereas allometric constants of leaf mass per shoot against stem length were smaller in monopodial species than in sympodial species. We propose that the allometries of current-year shoots reflect their function as disposable units for temporary leaf arrangement.

Journal Article↗