Ionospheric convection dynamics is an important window for understanding the coupling of the solar wind and interplanetary magnetic field to the Earth's ionosphere and upper atmosphere. In this study, we use measurements of ionospheric convection made by the SuperDARN radars to investigate the role of interhemispheric magnetic conjugacy in magnetosphere-ionosphere coupling and study the large-scale interactions between the magnetosphere and ionosphere. SuperDARN radars cover large geographic regions in both hemispheres and have a dataset spanning more than a decade, making them ideal for such studies. We begin in chapter 2 with an analysis of the degree of interhemispheric conjugacy exhibited in a Sub-Auroral Polarization Stream (SAPS). We present simultaneous observations of a SAPS event in both hemispheres made by mid-latitude SuperDARN radars with magnetically conjugate fields-of-view. An interhemispheric comparison of the characteristics of the SAPS channel reveals that the channel was conjugate in terms of potential variations across the channel even though substantial differences in latitudinal width and electric fields were observed in the channel. In chapter 3, we use interhemispheric SuperDARN observations of high latitude ionospheric convection in the noon-dusk sector to investigate the effects of IMF By penetrating into the closed magnetic field line region. The observations support the existence of an IMF By associated interhemispheric potential difference and field-aligned current system resulting in the generation of the interhemispheric asymmetries in ionospheric convection. Four events are analyzed in this study and the strength of interhemispheric currents associated with IMF By are estimated. Moreover, the strength of the interhemispheric currents is found to depend on the magnitude of IMF By, proximity of the currents to open-closed field line boundary, ionospheric conductivity and magnetic local time. In chapter 4, we use data from the mid-latitude SuperDARN radars between Jan-2011 and Aug-2012 to compile a database of SAPS events spanning about six hours in magnetic local time. The event database is used to analyze the average spatial variations in the occurrence rate and velocities of the SAPS channel under different geomagnetic conditions. An empirical model based on Dst-index is then developed to estimate the occurrence rate of SAPS at a given latitude and magnetic local time. / Ph. D.

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No description available.

The primary motor cortex (M1) contains a somatotopic progression with highly overlapping areas outputting to muscles of the upper limb. This organization is modified by muscle activity and neurological injury such as spinal cord injury (SCI). To date, bilateral M1 organization in controls and SCI has been minimally explored, and no study has examined the cortical territory that directs output to multiple muscles thought to be involved in movement synergies. An initial study was conducted to characterize the bilateral organization and representational overlap for muscles of the upper limb in incomplete spinal cord injury relative to uninjured individuals. Differences in symmetry and amount of overlapping territory were observed between groups, possibly reflecting differences in synergistic muscle use. The second study examined transcallosal communication between the two motor cortices and its role in dynamically modulating motor representations during unilateral contraction. The depth of interhemispheric inhibition (IHI) was examined in a muscle of the right hand by delivering a conditioning stimulus to ipsilateral M1 followed by a test stimulus to contralateral M1. Reduced IHI corresponded to larger cortical territory, a relationship that existed for both contralateral and ipsilateral contraction. These data demonstrate that the magnitude of IHI in a hand muscle predicts the size of the cortical territory occupied by that muscle. We present a mechanistic model to explain these findings that further elucidate the role of interhemispheric communication in shaping motor output. This interaction between transcallosal inhibition and motor output may act as a component to experience-dependent plasticity within M1. By targeting this interaction, it may be possible to facilitate motor learning and performance or promote recovery of function following neurological injury. Further study examining the role of various intracortical circuits on representational plasticity and modulation of these interactions may yield advances in both basic and clinical neuroscience. / Thesis / Master of Science (MSc)

Les informations visuelles sont prépondérantes pour guider le comportement. Malgré une bonne connaissance du système visuel, un phénomène représentant une latéralisation de celui-ci, le phénomène de dominance oculaire (DO), reste mal compris et finalement peu étudié. Nos travaux de thèse ont permis de démontrer que cette DO exerce une large influence sur différentes étapes de la transformation des informations visuelles en mouvements manuels ou oculaires et que celle-ci s’exprime en interaction avec d’autres latéralisations du système nerveux telles que les latéralisations manuelle et des réseaux attentionnels. Nous montrons également son influence sur les processus de transfert d'information entre les deux hémisphères du cerveau. Enfin, nos travaux comportent des retombées cliniques directes : ils introduisent une méthode de quantification plus précise de la DO utilisable par les cliniciens pour une meilleure réussite de certaines techniques chirurgicales. En conclusion, nous montrons que la DO constitue un aspect important de la latéralisation du cerveau humain, relativement négligé jusqu’à présent. / Processing of visual information from the environment is preponderant for the successful performance of many motor behaviors. Despite a good knowledge of the visual system, a phenomenon corresponding to a lateralization of this system, called eye dominance (ED), remains not well understood and poorly studied. Our thesis demonstrated that ED has a widespread influence on different levels of the transformation of visual information into manual or ocular movements and interacts with other lateralizations of the central nervous system such as the manual and attentional networks. We also show the influence of ED on the process of information transfer between the two hemispheres of the brain. Finally, our work has direct clinical implications: it introduces a more accurate method of quantifying ED which is usable by clinicians for better success of some surgical techniques. In sum, we show that ED is an important aspect of the human brain lateralization which has been overlooked until now.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19889号 / 医博第4138号 / 新制||医||1016(附属図書館) / 32966 / 京都大学大学院医学研究科医学専攻 / (主査)教授 古川 壽亮, 教授 髙橋 良輔, 教授 富樫 かおり / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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No description available.

<p>The control of unimanual and bimanual tasks is a highly orchestrated process in which primary motor cortex (M1) and primary somatosensory cortex (SI) play key roles. While somatic cortices are known to aid in the control of hand movements, the neural mechanisms by which they act remain largely unknown. One mechanism which is thought to mediate the control of hand movements between bilateral M1s is called interhemispheric inhibition (IHI), a neurophysiological mechanism by which one M1 is able to inhibit the contralateral M1, reducing the occurrence of unwanted movements, or enabling the performance of two differing tasks. Previous research suggests that IHI may be one mechanism by which SI aids in the control of hand movements and this thesis further examined this relationship. Two experiments were performed to investigate the influence of SI on IHI. Experiment 1 investigated the effects of direct modulation of SI cortical excitability on IHI. Experiment 2 investigated the effects of peripheral somatosensory inputs on IHI. The collective results of Experiments 1 and 2 suggest that SI can indeed modulate IHI from either the cortical or peripheral level, with increases in IHI seen following either intervention. Further, it was found that SI selectively modulates only the short latency phase of IHI (SIHI) as well as that mixed afferent inputs were most effective in altering SIHI. The novel findings of this thesis suggest that SI is indeed capable of aiding in the control of motor outputs and thus may be a possible target in future rehabilitative strategies.</p> / Master of Science in Kinesiology

The deep convection from monsoons is known to be a major source of gravity waves in the Earth's summer troposphere. While propagating through the middle atmosphere, these waves can carry their momentum up to the mesosphere, following either a vertical or an oblique path. This upward and oblique propagation of gravity waves refers to the latitudinal propagation, away from their low-latitude tropospheric source and towards the polar summer mesosphere. Their dissipation in this atmospheric region plays an important role in the global dynamical structure of the middle atmosphere and yet, the oblique propagation of gravity waves is not included in the present global models. Understanding the influence of the obliquely propagating monsoon gravity waves on the polar summer mesosphere, as well as the hemispheric and seasonal variations of this phenomenon, can improve the gravity-wave parameterization schemes used in the global models. My dissertation relies upon the atmosphere theory and the gravity-wave observations, first, to perform an observational analysis of the oblique propagation of gravity waves in the summer hemisphere. In response to temperature anomalies in the winter northern stratosphere, the distribution of the gravity-wave pseudomomentum flux in the opposite summer mesosphere appeared to be altered. This in turn changes the gravity-wave oblique propagation and its influence on the temperature variations seen in the polar mesospheric clouds. After the development of a 4-D non-hydrostatic ray-tracing model for the simulation of the gravity-wave propagation, my dissertation explores the hemispheric and seasonal differences in the propagation and dissipation of more than 40,000 gravity waves from the low-latitude troposphere. These ray-tracing simulations show the southern hemisphere to be more conducive to both the vertical and the oblique propagation of tropospheric to mesospheric gravity waves. This analysis also highlighted a strong wave filtering at the northern tropopause where a significant number of gravity waves were vertically reflected before reaching the stratosphere. / Doctor of Philosophy / The propagation of waves throughout the Earth's atmosphere is a key phenomenon to understanding the global atmosphere dynamics. These atmospheric waves are known to change the temperature, the pressure, the density and the composition of the middle atmosphere. As a wave propagates upward, the density of the atmospheric background exponentially decreases, resulting in an exponential increase in the wave amplitude and thus, an exponential increase in the energy carried by the wave. When the wave breaks, this energy is released and transferred to the background flow. Gravity waves are part of the atmospheric wave spectrum that is of interest to the scientific community. While small-scale gravity waves can form from tropospheric instabilities such as an unbalanced flow over the mountains or a deep convection from monsoon or thunderstorms, they can propagate up to the upper mesosphere where they can break and transfer a significant amount of energy to the background flow. Although the significant role of these gravity waves in the coupling mechanisms between atmospheric regions is without dispute, their horizontal scale is too small to be resolved by most of the global-scale atmospheric models. The deep convection from monsoon regions is known to be a major source of mesospheric GWs and previous studies on summer northern hemisphere have shown that monsoon GWs tend to propagate obliquely from the low-latitude stratopause up to the high-latitude mesopause. We focus the observational study on the summer southern hemisphere and the Inter-Hemispheric Coupling (IHC) between the summer mesopause, where Polar Mesospheric Clouds (PMCs) form, and the winter stratosphere where sudden warmings occur. PMCs are excellent indicators of atmospheric changes. Their correlations with wind, temperature and GW pseudomomentum flux highlight the consequences of anomalies in the winter stratosphere, such as warmings, on the oblique propagation of GWs that influence the PMC formation in the summer southern hemisphere. After the computation of a ray-tracing model for the simulation of the gravity-wave propagation, a hemispheric and seasonal comparison of the tropospheric to mesospheric gravity-wave propagation based on four simulations highlights the spectral nature of this phenomenon.