Transient Response of the Head Kinematics - Influence of a Disturbed Visual Flow

Vision influences the controlled kinematics of human body. Previous studies have shown the influence of vision on head stabilization or whole posture. However, latencies between the stimuli and the head motion have never been quantified. The aim of this study is to quantify the influence of a perturbed vision on the head kinematics. Seven healthy volunteers without uncorrected vision (26.7±6.9 years old, 1 female, 2 right-handed/right-dominant eye, 5 right-handed/left-dominant eye) were studied. Visual stimuli were performed through an immersive personal 3D viewer (HMZ-T1, Sony), securely tied on the head. Motion analysis of the head and the torso were performed using the optoelectronic Vicon system (100Hz). Three markers were glued on the personal viewer, close to the nasion, left and right tragus, in order to create the head frame. Three markers were glued to create the torso frame (both acromia and C7). Two different 3D animated scenes were created on Blender and displayed at 24Hz. The first animation was a landscape with a ball rolling on the ground, and then the ball stopped before being virtually launched via a catapult toward the screen. Two velocities were programmed: 4.67 and 10.58 m.s-1. The second animation was a beach with sea and sky, where horizon tilted anticlockwise at 2 different constant rates: 0.24 deg.s-1 and 0.48 deg.s-1 with maximal amplitude of 8° and 16° respectively. The motion of the head relative to the torso was calculated for both scenes on seated and upright position, at the 2 different velocities, 2 times each, for a total of 16 random tests on each volunteer. For the launched ball animated scene, the reaction time seated was, as expected, shorter for the fast launches. For the beach animated scene, the head profiles followed most of the time the kinematic profile of the tilted animation, linearly or by steps, and not necessary until the end. Volunteers who were right-handed and right dominant eye tilted their head clockwise, at the inverse of the stimuli. Both experiments confirmed that visual stimulus could influence the kinematics of the head-neck system. In the ball animation, velocity of the stimulus does not seem to affect the amplitude of movement. In the beach animation, the head motions were variable, but performed at the same mean speed than the stimuli. Furthermore, the limited number of volunteer cannot conclude on the direction of rotation of the head, depending of the dominant hand and eye

Contribution des régions fronto-striatales dans les fonctions exécutives

Des études récentes ont montré que le noyau caudé interagissait avec le cortex préfrontal et qu’il pourrait être impliqué dans les fonctions exécutives. Le but de cette thèse était d’étudier la contribution du noyau caudé dans les fonctions exécutives, plus précisément dans des tâches de monitoring et de changement de règle, et d’observer comment ces régions fronto-striatales interagissent avec le réseau par défaut (RPD). Dans un premier temps, nous avons étudié le rôle du noyau caudé dans les deux types de monitoring : le monitoring d’origine interne, consistant à effectuer un suivi sur l’état de l’information en mémoire de travail afin de pouvoir faire un choix subséquent, et dans le monitoring d’origine externe où le suivi sur l’état des items est effectué par l’individu, mais la sélection est exécutée par une source externe. Il a été montré que le cortex préfrontal dorsolatéral (CPFDL) est impliqué dans les deux types de monitoring. À l’aide de l’imagerie par résonance magnétique fonctionnelle (IRMf), nos résultats ont montré une augmentation significative du signal BOLD au niveau du CPFDL dans les contrastes des conditions de monitoring d’origine interne et monitoring d’origine externe par rapport à la condition contrôle. De manière plus importante, une augmentation significative de l’activité a été observée dans le noyau caudé seulement dans les soustractions impliquant le monitoring d’origine interne par rapport à la condition contrôle, et par rapport à la condition de monitoring d’origine externe. En deuxième lieu, des études ont montré une contribution spécifique des régions fronto-striatales dans l’exécution d’un changement de règle. Toutefois, l’effet d’un changement de règle sur l’activité cérébrale n’a jamais été étudié sur les essais subséquents. À l’aide de l’IRMf, le cortex préfrontal ventrolatéral (CPFVL) et le noyau caudé ont montré une augmentation significative de leur activité lors des changements de règle continus et lors des changements de règles sporadiques par rapport à la condition contrôle, et aussi lors des essais où le maintien d’une même règle devait être effectué pour une courte durée par opposition au contrôle. Cependant, aucune activité fronto-striatale n’a été observée lorsqu’une même règle devait être appliquée pour une plus longue période. De plus, une diminution significative de l’activité du noyau caudé a été observée lors de la répétition de l’exécution d’une même règle suggérant une meilleure intégration de cette dernière. Finalement, plusieurs études ont montré une déactivation du RPD lors de l’exécution de tâches. À l’aide de l’IRMf, nous avons posé l’hypothèse que le RPD serait corrélé négativement avec les régions fronto-striatales lors de l’exécution d’une tâche de changement de règle. Nos résultats montrent une augmentation significative de l’activité des régions fronto-striatales lors d’une augmentation du nombre d’essais de changement de règle consécutif, pendant que le RPD montre une déactivation continue. De façon intéressante, pendant que les régions fronto-striatales montrent une diminution de leur activité lors de l’exécution d’une même règle pour une longue période, le RPD augmente son activité de façon significative. On conclut donc que le noyau caudé joue un rôle important dans la planification d’une nouvelle action lorsque plusieurs possibilités doivent être considérées en mémoire de travail, et ce en même temps. Finalement, le RPD montre une corrélation négative avec les régions fronto-striatales suggérant sa participation dans l’intégration d’une tâche devenant de plus en plus familière.Recent studies have shown that the caudate nucleus interacts with the prefrontal cortex, and that it is involved in executive processes. The goal of the thesis was to investigate the role of the caudate nucleus in executive processes, and to observe how the frontostriatal regions are interacting with the default mode network (DMN). Firstly, we studied the role of the caudate nucleus in self-ordered monitoring, which consist of keeping track of which stimuli have been selected and which remains to be selected, and externally-triggered monitoring, which refers to keeping track of one’s selection when an external source is performing the selection. It has been shown that de dorsolateral prefrontal cortex (DLPFC) was particularly involved in both types of monitoring. Using functional magnetic resonance imaging (fMRI), a significant increase of activity has been observed in the DLPFC during both monitoring conditions vs control condition. Importantly, significant increased activity in the caudate nucleus was observed only in subtractions involving self-ordered monitoring (the self-ordered vs control and self-ordered vs externally-triggered conditions). Secondly, previous studies have shown a specific contribution of frontostriatal regions during set-shifting. However, the effect of set-shifting on subsequent trials had yet to be determined. Using fMRI, significant increase of activity was observed in the ventrolateral prefrontal cortex (VLPFC) and the caudate nucleus during shifting trials versus control and in trials where the same rule was applied for a few trials before a set-shift occurred. However, no frontostriatal activity was observed when the same rule was applied for a longer period. Decreased activity in the caudate nucleus correlated with increasing trial position in trials where no set-shift occurred, suggesting that the more a rule is executed, the better it is established. Finally, several studies have shown a deactivation of the DMN during the execution of a goal-directed task. Using fMRI, we hypothesized that the DMN was negatively correlated with the frontostriatal regions during the execution of a set-shifting task. Our results showed a significant increase of activity in the frontostriatal regions as more set-shifts are being performed while the DMN gets more deactivated. Interestingly, as decreased activity was observed in the frontostriatal regions during the execution of the same rule for a long period, the DMN showed increasing activity. We concluded that the caudate nucleus is specifically involved during the planning of a novel action when several possibilities are available at the same time. Finally, the DMN shows a negative correlation with the frontostriatal regions suggesting its contribution to the execution of a more familiar task

Differential involvement of the anterior temporal lobes in famous people semantics

The ability to recognize a famous person occurs through semantic memory. Previous neuroimaging studies have shown that the anterior temporal lobes (ATLs) are involved in the recognition of famous people. However, it is still a matter of debate whether the semantic processing of names or pictures of famous people has an impact on the activation of ATLs. The aim of this study was to explore the pattern of activation associated with a semantic processing of famous people based on face and written name stimuli. Fifteen healthy young individuals participated in our fMRI study, in which they were asked to perform a semantic categorization judgment task, based on profession, of visually presented pictures, and names of famous people. Neuroimaging findings showed a common pattern of activation for faces and names mainly involving the inferior frontal regions, the posterior temporal lobe, the visual cortex, and the ATLs. We found that the comparison names vs. pictures lead to significant activation in the anterior superior temporal gyrus. On the other hand, faces vs. names seemed associated with increased activation in the medial ATL. Moreover, our results demonstrated that the functional connectivity network anchored to the medial ATL, compared to the anterior STG, is more connected to the bilateral occipital lobe and fusiform gyrus that are regions implicated in the visual system and visual processing of faces. This study provides critical evidence of the differential involvement of ATL regions in semantics of famous people

Rapid response to the M_w 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altered gray matter structural covariance networks in early stages of Alzheimer's disease

Clinical symptoms observed in Alzheimer's disease (AD) patients may reflect variations within specific large-scale brain networks, modeling AD as a disconnection syndrome. The present magnetic resonance imaging study aims to compare the organization of gray matter structural covariance networks between 109 cognitively unimpaired controls (CTRL) and 109 AD patients positive to beta-amyloid at the early stages of the disease, using voxel-based morphometry. The default-mode network (DMN; medial temporal lobe subsystem) was less extended in AD patients in comparison with CTRL, with a significant decrease in the structural association between the entorhinal cortex and the medial prefrontal and the dorsolateral prefrontal cortices. The DMN (midline core subsystem) was also less extended in AD patients. Trends toward increased structural association were observed in the salience and executive control networks. The observed changes suggest that early disruptions in structural association between heteromodal association cortices and the entorhinal cortex could contribute to an isolation of the hippocampal formation, potentially giving rise to the clinical hallmark of AD, progressive memory impairment. It also provides critical support to the hypothesis that the reduced connectivity within the DMN in early AD is accompanied by an enhancement of connectivity in the salience and executive control networks

Differential involvement of the anterior temporal lobes in famous people semantics

The ability to recognize a famous person occurs through semantic memory. Previous neuroimaging studies have shown that the anterior temporal lobes (ATLs) are involved in the recognition of famous people. However, it is still a matter of debate whether the semantic processing of names or pictures of famous people has an impact on the activation of ATLs. The aim of this study was to explore the pattern of activation associated with a semantic processing of famous people based on face and written name stimuli. Fifteen healthy young individuals participated in our fMRI study, in which they were asked to perform a semantic categorization judgement task, based on profession, of visually presented pictures and names of famous people. Neuroimaging findings showed a common pattern of activation for faces and names mainly involving the inferior frontal regions, the posterior temporal lobe, the visual cortex and the anterior temporal lobes. We found that the comparison names vs. pictures lead to significant activation in the anterior superior temporal gyrus. On the other hand, faces vs. names seemed associated with increased activation in the medial ATL. Moreover, our results demonstrated that the functional connectivity network anchored to the medial ATL, compared to the anterior STG, is more connected to the bilateral occipital lobe and fusiform gyrus that are regions implicated in the visual system and visual processing of faces. This study provides critical evidence of the differential involvement of ATL regions in semantics of famous people