A study of synchronization of nonlinear oscillators: Application to epileptic seizures

This dissertation focuses on several problems in neuroscience from the perspective of nonlinear dynamics and stochastic processes. The first part concerns a method to visualize the idea of the power spectrum of spike trains, which has an educational value to introductory students in biophysics. The next part consists of experimental and computational work on drug-induced epileptic seizures in the rat neocortex. In the experimental part, spatiotemporal patterns of electrical activities in the rat neocortex are measured using voltage-sensitive dye imaging. Epileptic regions show well-synchronized, in-phase activity during epileptic seizures. In the computational part, a network of a Hodgkin-Huxley type neocortical neural model is constructed. Phase reduction, which is a dimension reduction technique for a stable limit cycle, is applied to the system. The results propose a possible mechanism for the initiation of the drug-induced seizure as a result of a bifurcation. In the last part, a theoretical framework is developed to obtain the statistics for the period of oscillations of a stable limit cycle under stochastic perturbation. A stochastic version of phase reduction and first passage time analysis are utilized for this purpose. The method presented here shows a good agreement with numerical results for the weak noise regime --Abstract, page iii

A study of the development and the challenges of science teaching materials using VR technology

The purpose of this study was to create and use VR contents as science teaching materials, and to clarify the problems in creating and using them and using them as teaching materials. Assuming that ordinary science teachers create VR content, we gave graduate students who have not learned programming the challenge of creating the VR content. Two types of contents were created using A-Frame, an open source framework. The theme of the contents created were observation of plants in the field and observation of somatic cell division. As the results of this study, it was found that even programming beginners can create simple content with A-Frame, however, programming skills are necessary to create more advanced content. Regarding use, it was pointed out that the perspective was too emphasized and unrealistic. When used as a teaching material, there was a possibility that learning would not be deeply satisfied with the VR experience alone. At present, the position of the VR contents as science teaching materials is unclear. Further practical research is required.本研究の一部は，JSPS科研費19K02708ならびに19K03144および17H01980の助成を受けて行った

Processing of single-photon responses in the mammalian On and Off retinal pathways at the sensitivity limit of vision

Visually guided behaviour at its sensitivity limit relies on single-photon responses originating in a small number of rod photoreceptors. For decades, researchers have debated the neural mechanisms and noise sources that underlie this striking sensitivity. To address this question, we need to understand the constraints arising from the retinal output signals provided by distinct retinal ganglion cell types. It has recently been shown in the primate retina that On and Off parasol ganglion cells, the cell types likely to underlie light detection at the absolute visual threshold, differ fundamentally not only in response polarity, but also in the way they handle single-photon responses originating in rods. The On pathway provides the brain with a thresholded, low-noise readout and the Off pathway with a noisy, linear readout. We outline the mechanistic basis of these different coding strategies and analyse their implications for detecting the weakest light signals. We show that high-fidelity, nonlinear signal processing in the On pathway comes with costs: more single-photon responses are lost and their propagation is delayed compared with the Off pathway. On the other hand, the responses of On ganglion cells allow better intensity discrimination compared with the Off ganglion cell responses near visual threshold. This article is part of the themed issue 'Vision in dim light'.Peer reviewe

A study on psychological training of eSports using digital games: Focusing on rhythm game

Incidentally, several studies have mentioned that digital games or video games have a positive impact on psychological skills (Green, et al., 2003; Pessoa, 2009; Anguera, et al., 2013). Thus, this study aimed to examine the psychological skills focusing on selective attention by comparing the power change in the beta wave band of the EEG during game play and the results of the trail making test (TMT) conducted before and after. Participants were ten male college students who usually play game for at least one hour per day, five days per week (age: M = 21.90 ± 1.96). This study adopted “Osu!” that is a free online rhythm game as an experimental task, because several articles mentioned that professional gamers usually use "Osu!" as a warming up or practice before gaming (Webb, 2019; Carpenter, 2019). Thus, “Osu!” is assumed to have the effect of enhancing the players’ psychological skills. In addition, the TMT part B is adopted to measure attention to speed, motor speed, visual screening, mental flexibility, perseverance, interference affinity and reaction inhibition. As a result of comparing change in biological attention extracted from the EEG during game play or baseline measurement, there is a significant difference in selective attentional state between baseline and while game play. In comparison of TMT indicated that processing speed in after rhythm game was tended to be faster than before play. Thus, this study might be indicated that rhythm game would be the one of the psychological or cognitive training tool for eSports

SERCA2a過剰発現ラットにおけるイソプロテレノール持続投与誘導肥大心の左室力学的エネルギー学的性質の変化

Overexpression of cardiac sarcoplasmic reticulum Ca2 +-ATPase (SERCA2a) has been suggested as a strategic intervention for cardiac failure. However, its benefit in wild-type (WT) rats with normal SERCA2a levels seems to be small. To investigate whether it would be beneficial in a cardiac failure model with down-regulated SERCA2a levels, we made a cardiac hypertrophy model using isoproterenol infusion (1.2 mg kg− 1 day− 1 for 1 or 4 weeks; TG-ISO1w and TG-ISO4w, respectively) in SERCA2a transgenic (TG) rats and compared these rats with littermate WT rats that underwent the same treatments (WT-ISO1w and WT-ISO4w). We analyzed the left ventricular (LV) mechanoenergetics in the excised heart using our original cross-circulation system. The downward shift of curvilinear LV end-systolic pressure–volume relations (ESPVRs) observed in WT-ISO4w rats was abolished in TG-ISO4w rats. The slope and VO2 intercept of the VO2 (myocardial oxygen consumption per beat)–PVA (systolic pressure–volume area: total mechanical energy per beat) linear relation did not differ in any of the groups. The most important finding was a significantly smaller O2 cost of LV contractility in the TG-ISO4w group, which means that less O2 is needed to exert the same LV contractility, compared with the other groups. The increased ratio of SERCA2a/phospholamban returned to the level of the WT-control group only in the TG-ISO4w group. Longer-term up-regulation of mitochondrial transcription factor A for genes of mitochondrial enzymes producing ATP was observed in TG rats. In conclusion, longer-term overexpression of SERCA2a will be beneficial in the present cardiac failure model with down-regulated SERCA2a levels.博士（医学）・甲619号・平成26年3月17

Frequency-Hopping Wave Engineering with Metasurfaces

Wave phenomena can be artificially engineered by scattering from metasurfaces, which aids in the design of radio-frequency and optical devices for wireless communication, sensing, imaging, wireless power transfer and bio/medical applications. Scattering responses vary with changing frequency; conversely, they remain unchanged at a constant frequency, which has been a long-standing limitation in the design of devices leveraging wave scattering phenomena. Here, we present metasurfaces that can scatter incident waves according to two variables - the frequency and pulse width - in multiple bands. Significantly, these scattering profiles are characterized by how the frequencies are used in different time windows due to transient circuits. In particular, with coupled transient circuits, we demonstrate variable scattering profiles in response to unique frequency sequences, which can markedly increase the available frequency channels in accordance with a factorial function. Our proposed concept, which is analogous to frequency hopping in wireless communication, advances wave engineering in electromagnetics and related fields.Comment: 62 pages, 25 figure

Higher order approximation of isochrons

Phase reduction is a commonly used techinque for analyzing stable oscillators, particularly in studies concerning synchronization and phase lock of a network of oscillators. In a widely used numerical approach for obtaining phase reduction of a single oscillator, one needs to obtain the gradient of the phase function, which essentially provides a linear approximation of isochrons. In this paper, we extend the method for obtaining partial derivatives of the phase function to arbitrary order, providing higher order approximations of isochrons. In particular, our method in order 2 can be applied to the study of dynamics of a stable oscillator subjected to stochastic perturbations, a topic that will be discussed in a future paper. We use the Stuart-Landau oscillator to illustrate the method in order 2

Examining effectiveness of e-sports activity in Japan

Digital games or video games have a positive impact on cognitive function. However, there is no study examining the positive effects of e-sports in Japan. Thus, we conducted two studies. Study 1 examined the relationship between e-sports and cognitive function using the Stroop and reverse-Stroop Color and Word Test. Additionally, study 2 examined the psychological statement while playing e-sports using biological evaluation. Study 1 included six male collegiate students who could play e-sports (three in the e-sports group, three in the control group), while study 2 involved two male Japanese collegiate e-sports players. The e-sports group played e-sports for 10 minutes and their cognitive function and psychological statement were evaluated during play. EEG was employed to evaluate the psychological statement of the e-sport players in study 2. Emotional condition (concentration) was analysed from the combination of the extracted raw EEG data using KANSEI Module Logger. Results of study 1 indicated that 10 minutes of e-sports activity significantly improved cognitive function, especially interference and concentration, in the e-sports group. Study 2 concluded that the average concentration value at play time was significantly higher than that during the resting period. Therefore, this study indicated that e-sports activity might have positive effects when played for a brief time

Making and using of two types of the simple magnifying projectors

Magnifying equipment is the basic tool for experiments of science classes. In the present study, two types of handmade magnifying projectors were developed. They were the non-screen type and the built-in screen type. Most of the materials of these projectors were obtained from the super-market or the Do-it-yourself stores. Lenses used for these tools were objective lenses and eye lenses of the common light microscope. The built-in screen type projector was used in the science class of the 1st grade of the junior high school. As the result, all students had actively observed crystals of the sodium chloride and the alum. This suggests that the handmade simple magnifying projectors were very effective for the student's activities in the science classes.本研究の一部は,科学研究費基盤研究A(25242015)の助成によ