Do we use a priori knowledge of gravity when making elbow rotations?

In this study, we aim to investigate whether motor commands, emanating from movement planning, are customized to movement orientation relative to gravity from the first trial on. Participants made fast point-to-point elbow flexions and extensions in the transverse plane. We compared movements that had been practiced in reclined orientation either against or with gravity with the same movement relative to the body axis made in the upright orientation (neutral compared to gravity). For each movement type, five rotations from reclined to upright orientation were made. For each rotation, we analyzed the first trial in upright orientation and the directly preceding trial in reclined orientation. Additionally, we analyzed the last five trials of a 30-trial block in upright position and compared these trials with the first trials in upright orientation. Although participants moved fast, gravitational torques were substantial. The change in body orientation affected movement planning: we found a decrease in peak angular velocity and a decrease in amplitude for the first trials made in the upright orientation, regardless of whether the previous movements in reclined orientation were made against or with gravity. We found that these decreases disappeared after participants familiarized themselves with moving in upright position in a 30-trial block. These results indicate that participants used a general strategy, corresponding to the strategy observed in situations with unreliable or limited information on external conditions. From this, we conclude that during movement planning, a priori knowledge of gravity was not used to specifically customize motor commands for the neutral gravity condition

Do Gravity-Related Sensory Information Enable the Enhancement of Cortical Proprioceptive Inputs When Planning a Step in Microgravity?

International audienceWe recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of the leg muscle. The vibration lasted 1 s and the participants were asked to either initiate a step at the vibration offset or to remain still. We found that the early SEP (90–160 ms) was smaller when the platform was translated than when it remained stationary, revealing the existence of an interference phenomenon (i.e., when proprioceptive stimulation is preceded by the stimulation of different sensory modalities evoked by the platform translation). By contrast, the late SEP (550 ms post proprioceptive stimulation onset) was greater when the translation preceded the vibration compared to a condition without pre-stimulation (i.e., no translation). This suggests that restoring a body reference system which is impaired in microgravity allowed a greater proprioceptive cortical processing. Importantly, however, the late SEP was similarly increased when participants either produced a step or remained still. We propose that the absence of step-induced facilitation of proprioceptive cortical processing results from a decreased weight of proprioception in the absence of balance constraints in microgravity

Multisensory interactions in Virtual Reality: optic flow reduces vestibular sensitivity, but only for congruent planes of motion

During exposure to Virtual Reality (VR) a sensory conflict may be present, whereby the visual system signals that the user is moving in a certain direction with a certain acceleration, while the vestibular system signals that the user is stationary. In order to reduce this conflict, the brain may down-weight vestibular signals, which may in turn affect vestibular contributions to self-motion perception. Here we investigated whether vestibular perceptual sensitivity is affected by VR exposure. Participants’ ability to detect artificial vestibular inputs was measured during optic flow or random motion stimuli on a VR head-mounted display. Sensitivity to vestibular signals was significantly reduced when optic flow stimuli were presented, but importantly this was only the case when both visual and vestibular cues conveyed information on the same plane of self-motion. Our results suggest that the brain dynamically adjusts the weight given to incoming sensory cues for self-motion in VR; however this is dependent on the congruency of visual and vestibular cues

Treatment of vestibular disorders with weak asymmetric base-in prisms: An hypothesis with a focus on Ménière’s disease

BACKGROUND: Regular treatments of Ménière's disease (MD) vary largely, and no single satisfactory treatment exists. A complementary treatment popular among Dutch and Belgian patients involves eyeglasses with weak asymmetric base-in prisms, with a perceived high success rate. An explanatory mechanism is, however, lacking. OBJECTIVE: To speculate on a working mechanism explaining an effectiveness of weak asymmetric base-in prims in MD, based on available knowledge. METHODS: After describing the way these prisms are prescribed using a walking test and its effect reported on, we give an explanation of its underlying mechanism, based on the literature. RESULTS: The presumed effect can be explained by considering the typical star-like walking pattern in MD, induced by a drifting after-image comparable to the oculogyral illusion. Weak asymmetric base-in prisms can furthermore eliminate the conflict between a net vestibular angular velocity bias in the efferent signal controlling the VOR, and a net re-afferent ocular signal. CONCLUSIONS: The positive findings with these glasses reported on, the fact that the treatment itself is simple, low-cost, and socially acceptable, and the fact that an explanation is at hand, speak in favour of elaborating further on this treatment

Characterization of the metabolic production of marine biofilms : Towards an application to the study of complex biofilms in situ

Le phénomène de biofouling est un processus naturel qui impacte toutes les surfaces immergées en milieu marin engendrant des problèmes économiques et écologiques majeurs à l’échelle planétaire. Il est notamment induit par la formation de biofilms marins correspondant à la colonisation des surfaces immergées par des bactéries s’organisant en communautés en s’entourant d’une matrice de substances polymériques extracellulaires (EPS). L’objectif de ce travail est l’utilisation et le développement de méthodologies permettant l’étude et la compréhension de l’étape précurseur de ce phénomène. La corrélation des données récoltées à partir des méthodes appliquées (métabolomique et réseau moléculaire, protéomique, dosages colorimétriques, microscopies, spectroscopies) permet une approche multi-échelles pour la caractérisation des biofilms. Ces développements visent, en premier lieu, à caractériser la production biochimique globale de biofilms in vitro pour ensuite analyser des biofilms naturels formés in situ. L’utilisation de ce large panel de techniques a permis de répondre à certaines questions scientifiques comme l’impact des nutriments (phosphates), d’une enzyme (quorum sensing) ou de l’hydrodynamisme sur la nature de biofilms formés.The phenomenon of biofouling is a natural process that impacts all the surfaces submerged in the marine environment, generating major economic and ecological problems on a global scale. It is induced by the formation of marine biofilms corresponding to the colonization of submerged surfaces by bacteria organizing in communities by surrounding themselves with a matrix of extracellular polymeric substances (EPS). The objective of this work is the use and development of methodologies to study and understand the precursor stage of this phenomenon. The correlation of the data collected from the applied methods (metabolomics and molecular network, proteomics, colorimetric assays, microscopies, spectroscopy) allows a multi-scale approach for the characterization of biofilms. These developments aim, first of all, to characterize the overall biochemical production of in vitro biofilms and then analyse natural biofilms formed in situ. The use of this wide range of techniques has made it possible to answer certain scientific questions such as the impact of nutrients (phosphates), an enzyme (quorum sensing) or hydrodynamics on the nature of formed biofilms

1. 4 février 1880 : Règlement relatif à renseignement de la lecture à haute voix dans les écoles communales de la ville de Paris

Carriot Eugène Hubert, Étienne, Joseph. 1. 4 février 1880 : Règlement relatif à renseignement de la lecture à haute voix dans les écoles communales de la ville de Paris. In: L'enseignement du Français à l'école primaire – Textes officiels. Tome 2 : 1880-1939. Paris : Institut national de recherche pédagogique, 1995. pp. 53-55. (Bibliothèque de l'Histoire de l'Education, 5

Caractérisation de la production métabolique de biofilms marins. : Vers une application à l'étude de biofilms complexes in situ

The phenomenon of biofouling is a natural process that impacts all the surfaces submerged in the marine environment, generating major economic and ecological problems on a global scale. It is induced by the formation of marine biofilms corresponding to the colonization of submerged surfaces by bacteria organizing in communities by surrounding themselves with a matrix of extracellular polymeric substances (EPS). The objective of this work is the use and development of methodologies to study and understand the precursor stage of this phenomenon. The correlation of the data collected from the applied methods (metabolomics and molecular network, proteomics, colorimetric assays, microscopies, spectroscopy) allows a multi-scale approach for the characterization of biofilms. These developments aim, first of all, to characterize the overall biochemical production of in vitro biofilms and then analyse natural biofilms formed in situ. The use of this wide range of techniques has made it possible to answer certain scientific questions such as the impact of nutrients (phosphates), an enzyme (quorum sensing) or hydrodynamics on the nature of formed biofilms.Le phénomène de biofouling est un processus naturel qui impacte toutes les surfaces immergées en milieu marin engendrant des problèmes économiques et écologiques majeurs à l’échelle planétaire. Il est notamment induit par la formation de biofilms marins correspondant à la colonisation des surfaces immergées par des bactéries s’organisant en communautés en s’entourant d’une matrice de substances polymériques extracellulaires (EPS). L’objectif de ce travail est l’utilisation et le développement de méthodologies permettant l’étude et la compréhension de l’étape précurseur de ce phénomène. La corrélation des données récoltées à partir des méthodes appliquées (métabolomique et réseau moléculaire, protéomique, dosages colorimétriques, microscopies, spectroscopies) permet une approche multi-échelles pour la caractérisation des biofilms. Ces développements visent, en premier lieu, à caractériser la production biochimique globale de biofilms in vitro pour ensuite analyser des biofilms naturels formés in situ. L’utilisation de ce large panel de techniques a permis de répondre à certaines questions scientifiques comme l’impact des nutriments (phosphates), d’une enzyme (quorum sensing) ou de l’hydrodynamisme sur la nature de biofilms formés

Réalisation d'objets en technologie, CM

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