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Search Results: 1 - 10 of 765 matches for " Kenichi Kuriyama "
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Right Prefrontal Activity Reflects the Ability to Overcome Sleepiness during Working Memory Tasks: A Functional Near-Infrared Spectroscopy Study
Motoyasu Honma,Takahiro Soshi,Yoshiharu Kim,Kenichi Kuriyama
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012923
Abstract: It has been speculated that humans have an inherent ability to overcome sleepiness that counteracts homeostatic sleep pressure. However, it remains unclear which cortical substrate activities are involved in the ability to overcome sleepiness during the execution of cognitive tasks. Here we sought to confirm that this ability to overcome sleepiness in task execution improves performance on cognitive tasks, showing activation of neural substrates in the frontal cortex, by using a modified n-back (2- and 0-back) working memory task and functional near-infrared spectroscopy. The change in alertness was just correlated with performances on the 2-back task. Activity in the right prefrontal cortex changed depending on alertness changes on the 2- and 0-back tasks independently, which indicates that activity in this region clearly reflects the ability to overcome sleepiness; it may contribute to the function of providing sufficient activity to meet the task load demands. This study reveals characteristics of the ability to overcome sleepiness during the n-back working memory task which goes beyond the attention-control function traditionally proposed.
Increased cerebral blood flow in the right frontal lobe area during sleep precedes self-awakening in humans
Aritake Sayaka,Higuchi Shigekazu,Suzuki Hiroyuki,Kuriyama Kenichi
BMC Neuroscience , 2012, DOI: 10.1186/1471-2202-13-153
Abstract: Background Some people can subconsciously wake up naturally (self-awakening) at a desired/planned time without external time stimuli. However, the underlying mechanism regulating this ability remains to be elucidated. This study sought to examine the relationship between hemodynamic changes in oxyhemoglobin (oxy-Hb) level in the prefrontal cortex and sleep structures during sleep in subjects instructed to self-awaken. Results Fifteen healthy right-handed male volunteers with regular sleep habits participated in a consecutive two-night crossover study. The subjects were instructed to wake up at a specified time (“request” condition) or instructed to sleep until the morning but forced to wake up at 03:00 without prior notice (“surprise” condition). Those who awoke within ± 30 min of the planned waking time were defined as those who succeeded in self-awakening (“success” group). Seven subjects succeeded in self-awakening and eight failed. No significant differences were observed in the amounts of sleep in each stage between conditions or between groups. On the “request” night, an increase in oxy-Hb level in the right prefrontal cortex and a decrease in δ power were observed in the “success” group around 30 min before self-awakening, whereas no such changes were observed in the “failure” group. On the “surprise” night, no significant changes were observed in oxy-Hb level or δ power in either group. Conclusions These findings demonstrate a correlation between self-awakening and a pre-awakening increase in hemodynamic activation in the right prefrontal cortex, suggesting the structure’s contribution to time estimation ability.
Sleep Dissolves Illusion: Sleep Withstands Learning of Visuo-Tactile-Proprioceptive Integration Induced by Repeated Days of Rubber Hand Illusion Training
Motoyasu Honma, Takuya Yoshiike, Hiroki Ikeda, Yoshiharu Kim, Kenichi Kuriyama
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0085734
Abstract: Multisensory integration is a key factor in establishing bodily self-consciousness and in adapting humans to novel environments. The rubber hand illusion paradigm, in which humans can immediately perceive illusory ownership to an artificial hand, is a traditional technique for investigating multisensory integration and the feeling of illusory ownership. However, the long-term learning properties of the rubber hand illusion have not been previously investigated. Moreover, although sleep contributes to various aspects of cognition, including learning and memory, its influence on illusory learning of the artificial hand has not yet been assessed. We determined the effects of daily repetitive training and sleep on learning visuo-tactile-proprioceptive sensory integration and illusory ownership in healthy adult participants by using the traditional rubber hand illusion paradigm. Subjective ownership of the rubber hand, proprioceptive drift, and galvanic skin response were measured to assess learning indexes. Subjective ownership was maintained and proprioceptive drift increased with daily training. Proprioceptive drift, but not subjective ownership, was significantly attenuated after sleep. A significantly greater reduction in galvanic skin response was observed after wakefulness compared to after sleep. Our results suggest that although repetitive rubber hand illusion training facilitates multisensory integration and physiological habituation of a multisensory incongruent environment, sleep corrects illusional integration and habituation based on experiences in a multisensory incongruent environment. These findings may increase our understanding of adaptive neural processes to novel environments, specifically, bodily self-consciousness and sleep-dependent neuroplasticity.
Sleep Deprivation Influences Diurnal Variation of Human Time Perception with Prefrontal Activity Change: A Functional Near-Infrared Spectroscopy Study
Takahiro Soshi,Kenichi Kuriyama,Sayaka Aritake,Minori Enomoto,Akiko Hida,Miyuki Tamura,Yoshiharu Kim,Kazuo Mishima
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0008395
Abstract: Human short-time perception shows diurnal variation. In general, short-time perception fluctuates in parallel with circadian clock parameters, while diurnal variation seems to be modulated by sleep deprivation per se. Functional imaging studies have reported that short-time perception recruits a neural network that includes subcortical structures, as well as cortical areas involving the prefrontal cortex (PFC). It has also been reported that the PFC is vulnerable to sleep deprivation, which has an influence on various cognitive functions. The present study is aimed at elucidating the influence of PFC vulnerability to sleep deprivation on short-time perception, using the optical imaging technique of functional near-infrared spectroscopy. Eighteen participants performed 10-s time production tasks before (at 21:00) and after (at 09:00) experimental nights both in sleep-controlled and sleep-deprived conditions in a 4-day laboratory-based crossover study. Compared to the sleep-controlled condition, one-night sleep deprivation induced a significant reduction in the produced time simultaneous with an increased hemodynamic response in the left PFC at 09:00. These results suggest that activation of the left PFC, which possibly reflects functional compensation under a sleep-deprived condition, is associated with alteration of short-time perception.
Playing the Deficit Gamble Easily  [PDF]
Kenichi Tamegawa
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.22037
Abstract: In this paper, we attempt to obtain the exact probability distribution of the debt-to-GDP ratio in T years, assuming that 1) the primary balance is zero and 2) the interest rate and the GDP growth rate are given as exogenous random variables. With this approach, researchers can play the “Deficit Gamble” without conducting a Monte Carlo simulation. Calculating the distribution of the debt-to-GDP ratio would be useful for policy planning.
A Biased Expectation Equilibrium in Indeterminate DSGE Models  [PDF]
Kenichi Tamegawa
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.23053
Abstract: The aim of this article is to introduce a solution method for an indeterminate dynamic stochastic general equilibrium (DSGE) model. The method uses the concept of a biased expectation equilibrium, which is defined in this paper and means that expectations of certain variable are mechanically biased against those that would be rational. Our method should be particularly useful in terms of empirical estimation using DSGE models, because it will allow researchers to estimate how much agents’ expectations are biased in the case where a model has indeterminacy.
Irradiance and Developmental Stages of Crown Architecture Affect Shoot Production in Rhododendron reticulatum  [PDF]
Kenichi Yoshimura
American Journal of Plant Sciences (AJPS) , 2013, DOI: 10.4236/ajps.2013.45A011

Plasticity in crown architecture, contributing to leaf arrangement within crown, is an important feature for whole plant carbon assimilation and survival. In this study, I examined the plasticity in crown architecture to light condition and developmental stage by the changes in shoot production. Rhododendron reticulatum expands crown with orthotropic growth in monopodial branching in young stage, but orthotropic growth is ceased in adult stage. Main stem of young crown is described with monopodial branching regardless of light environment. But multi-layer crown is observed in sun-lit environment rather than mono-layer crown in adult stage. Long shoot production for each branching system (foliage derived from sympodial branching) in young crown is associated with local light environment, but not in adult crown. Long shoot production rate is correlated with long shoot production rate of its mother shoot in young crown, but not in mono-layer crown. These results suggest that young crown expands branches to sun-lit position whereas adult crown reduces congestion of shoots with stochastic shoot production regardless of shoot production of mother shoots. I concluded that both light and developmental stage are important factors for shoot production and constructing crown architecture.

Erratum to “Irradiance and Developmental Stages of Crown Architecture Affect Shoot Production in Rhododendron reticulatum” [American Journal of Plant Sciences 4 (2013) 69-76]  [PDF]
Kenichi Yoshimura
American Journal of Plant Sciences (AJPS) , 2014, DOI: 10.4236/ajps.2014.513214

The original online version of this article (Yoshimura, K. (2013) Irradiance and Developmental Stages of Crown Architecture Affect Shoot Production in Rhododendron reticulatum. American Journal of Plant Sciences, 4, 69-76. http://dx.doi.org/10.4236/ajps.2013.45A011) was published as a single-author paper mistakenly. To reflect the contribution and responsibility of the second author as well as the affiliations of the authors at the time of the study, we have revised the authorship and author affiliations of this article. The author wishes to correct the errors as:

Kenichi Yoshimura1,2, Hiroaki Ishii1

1Graduate School of Science and Technology, Kobe University, Kobe, Japan

2Present Address: Center for Ecological Research, Kyoto University, Otsu, Japan


Mechanical Properties of a Vacuum-Sintered Apatite Body for Use as Artificial Bone  [PDF]
Kenichi Tamura
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2015, DOI: 10.4236/jbnb.2015.61005

Regenerative artificial bone material and bone parts were fabricated using vacuum-sintered bodies of a “titanium medical apatite (TMA?)” that is formed by chemically connecting Ti oxide molecules to the reactive [Ca10 (PO4 )6 ] group of hydroxyapatite (HAp). Sintering at temperatures of 1273 - 1773 K caused this TMA sintered bodies to recrystallize and form a varying mix of α-TCP (tricalcium phosphate), β-TCP and Perovskite-CaTiO3 phases. The Perovskite crystals proved to be quite stable and hard, forming a uniform distribution of similarly sized fibers in all directions under vacuum sintering, but an irregular distribution and size when sintered in the presence of oxygen. Complete recrystallization was achieved by vacuum sintering at temperatures in excess of 1473 K. In particular, TMA vacuum-sintered bodies at 1573 K are given the maximum value; a Vickers hardness of 400, a bending strength of 43 MPa, a compressive strength of 270 MPa and a density of approximately 2300 kg/m3 was achieved that closely corresponds to that of compact bone or a tooth. As these TMA bodies could also be cut into various forms, they are considered a promising biomaterial for use as artificial bone in the regeneration of natural bone, or to provide reinforcement of bone junctions in dental and orthopedic surgery.

Learning Algorithm for Relation-Substitutable Context-Free Languages
Takayuki Kuriyama
Computer Science , 2014,
Abstract: We generalized the class of $k,l$-substitutable languages (Yoshinala, 2008). Each language in the generalized class is closed under a good substitutability. The substitutability is defined by a recognizable equivalence relation. We show the convergence of our generalized learning algorithm. The size of the characteristic sample is smaller than Yoshinaka's.
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