Étude pilote de l’effet d’un entraînement utilisant une stimulation sensorielle par vibrations reproduisant la marche chez des personnes hémiparétiques

La plupart des personnes hémiparétiques à la suite d’un accident vasculaire cérébral présentent des atteintes de la marche qui limitent leur participation sociale. Pour optimiser la récupération, l'entraînement prolongé à la marche est aujourd'hui recommandé. Cette approche est fondée sur l'importance des informations sensorielles de mouvement pour récupérer le meilleur contrôle du mouvement possible. Ces informations peuvent aussi être fournies par des vibrations musculaires localisées. L'application séquentielle et structurée de vibrations sur différents muscles des membres inférieurs peut ainsi mimer l'activité sensorielle associée aux mouvements de la marche normale. L’objectif de ce projet était d’évaluer l’effet d’un entraînement utilisant des vibrations reproduisant l’activité sensorielle de la marche sur les paramètres de marche de personnes hémiparétiques en phase de réadaptation fonctionnelle intensive. Pour cela, une étude expérimentale à cas uniques avec des mesures répétées a été menée auprès de trois personnes hémiparétiques. Chaque participant a reçu l’entraînement par vibrations à raison de quatre séances de 30 minutes par semaine pendant trois semaines. La vitesse de marche au sol à vitesse confortable et rapide, mesures principales de résultat, ainsi que les autres paramètres spatio-temporels de la marche et le patron de marche ont été collectés à deux reprises avant l’entraînement, à la fin de chaque semaine d’entraînement puis un mois après la fin de la période d’entraînement. Les vitesses de marche au sol de participants hospitalisés en réadaptation fonctionnelle intensive issues d’une base de données ont été utilisées afin de comparer les résultats obtenus avec les trois participants au projet. Une augmentation de la vitesse de marche au sol a été observée uniquement chez un des trois participants. Ce changement a été observé dès la première semaine d’entraînement et était supérieur à ceux obtenus chez les participants issus de la base de données. L’entraînement par vibrations a cependant permis d'améliorer les autres paramètres spatio-temporels et le patron de marche des trois participants. Au regard de ces résultats, il est nécessaire de poursuivre l’évaluation de l’entraînement par vibrations afin de mieux comprendre ses effets et de développer un nouvel outil de réadaptation.Most of individuals with hemiparesis following a stroke present gait disabilities which limit their social participation. Prolonged gait training is recommended to optimize the recovery. This approach is founded on the importance of the sensory information produced by gait movements to recover the best possible control of movement. This information could also be induced by means of multiple localized muscular vibration. It has been showed that sequential and patterned vibration application on different muscles of lower limbs could mimic sensory activity associated with normal gait movement. The purpose of this project was to evaluate the effect of gait-like vibration training on gait parameter in hemiparetic people in subacute phase. To answer this question, a single case experimental design study with repeated measures was used with three individuals with hemiparesis during intensive functional rehabilitation. Each participant has received gait-like vibration training in 30-minute sessions, four times per week for three weeks. Comfortable and fast overground gait speeds were the principal outcome measures. Spatiotemporal data and gait pattern were also evaluated. Each data was collected twice before training, then at the end of each week of training and a month after the end of the training. Control data of overground gait speeds of individuals with hemiparesis in the same intensive rehabilitation facility, prospectively collected in a clinical database, has been used to compare the additional effect gait speed of the three participants. An increase of overground gait speed has been observed in only one of the three participants. This change appeared at the end of the first week of training and were superior to these obtained in the database participants. Gait-like vibration training has also permitted an improvement of the other spatiotemporal data and gait pattern of all three participants. Regarding these results, it seems necessary to continue the evaluation of gait-like vibration training to better understand these effects and develop a new tool of rehabilitation

Gait-like vibration training improves gait abilities: a case report of a 62 year old person with a chronic incomplete spinal cord injury

The purpose of this single-subject case study was to quantify the effect of gait-like vibration training on gait abilities after an incomplete spinal cord injury. A 62 year old male with a chronic AIS D spinal cord injury at T11 completed nine sessions of gait-like vibration training in a standing position. Self-selected gait speed and distance covered within 6 minutes were determined before and after training to evaluate the impact of training on gait performance. Associated changes in gait kinematics were assessed with a 3D motion analysis system. Results showed an improvement of gait speed (0.26 m/s vs 0.35 m/s) and distance (23 m vs 37m) after nine gait-like vibration training sessions (+34.6%; +60.9%). In addition, more bilateral hip extension and larger left hip range of motion improved hip-knee cyclograms. Gait-like vibration training improved gait abilities in a person with chronic incomplete spinal cord injury

Oxide spin-orbitronics: New routes towards low-power electrical control of magnetization in oxide heterostructures

International audienceThe transition metal oxide family harbors various types of materials of interest for spintronics: half-metallic manganites are highly efficient spin injectors and detectors, yielding record values of tunnel magnetoresistance; multiferroic materials, and in particular BiFeO 3 , allow the electrical control of magnetization and spin excitations at room temperature; combined with ferromagnets, piezoelectric perovskites enable a controlled tuning of magnetic anisotropy, domain dynamics and even magnetic order. In this review, we argue that a new opportunity is emerging for oxides in spintronics with the rise of spin-orbit-driven phenomena such as the direct and inverse spin Hall and Rashba-Edelstein effects. After surveying the few results reported on inverse spin Hall measurements in oxide materials, we describe in depth the physics of SrTiO 3-based interfaces and their usage for both spin-to-charge and charge-to-spin conversion. Finally, we give perspectives for a more thorough exploration of spin Hall effects in oxides and enhanced conversion ratios in both three-and two-dimensional structures

Growth and magnetic properties of multiferroic LaxBi1-xMnO3 thin films

A comparative study of LaxBi1-xMnO3 thin films grown on SrTiO3 substrates is reported. It is shown that these films grow epitaxially in a narrow pressure-temperature range. A detailed structural and compositional characterization of the films is performed within the growth window. The structure and the magnetization of this system are investigated. We find a clear correlation between the magnetization and the unit-cell volume that we ascribe to Bi deficiency and the resultant introduction of a mixed valence on the Mn ions. On these grounds, we show that the reduced magnetization of LaxBi1-xMnO3 thin films compared to the bulk can be explained quantitatively by a simple model, taking into account the deviation from nominal composition and the Goodenough-Kanamori-Anderson rules of magnetic interactions

Structural and functional characterization of (110)-oriented epitaxial La2/3Ca1/3MnO3 electrodes and SrTiO3 tunnel barriers

La2/3Ca1/3MnO3 (LCMO) films have been deposited on (110)-oriented SrTiO3 (STO) substrates. X-ray diffraction and high-resolution electron microscopy reveal that the (110) LCMO films are epitaxial and anisotropically in-plane strained, with higher relaxation along the [1¿10] direction than along the [001] direction; x-ray absorption spectroscopy data signaled the existence of a single intermediate Mn3+/4+ 3d-state at the film surface. Their magnetic properties are compared to those of (001) LCMO films grown simultaneously on (001) STO substrates It is found that (110) LCMO films present a higher Curie temperature (TC) and a weaker decay of magnetization when approaching TC than their (001) LCMO counterparts. These improved films have been subsequently covered by nanometric STO layers. Conducting atomic-force experiments have shown that STO layers, as thin as 0.8 nm, grown on top of the (110) LCMO electrode, display good insulating properties. We will show that the electric conductance across (110) STO layers, exponentially depending on the barrier thickness, is tunnel-like. The barrier height in STO (110) is found to be similar to that of STO (001). These results show that the (110) LCMO electrodes can be better electrodes than (001) LCMO for magnetic tunnel junctions, and that (110) STO are suitable insulating barriers

Adaptive Kerr-assisted transverse mode selection in multimode fibers

Multimode optical fibers (MMFs) have recently regained interest because of the degrees of freedom associated with their different eigenmodes. In the nonlinear propagation regime in particular, new phenomena have been unveiled in graded-index (GRIN) MMFs such as geometric parametric instabilities and Kerr beam self-cleaning [1, 2]. The speckled pattern observed at the output of the MMF at low powers, is transformed at high powers into a bell-shaped beam close to the fundamental mode. Recent work has also demonstrated that Kerr beam self-cleaning can lead to a low-order spatial mode, different from a bell-shape, by adjusting the laser beam in-coupling conditions [3]. An attractive way to systematically control the spatial excitation conditions at the fiber input is provided by the use of a spatial light modulator (SLM) which permits to profile the beam wavefront entering the MMF. In most cases, experiments involving adaptive optics consider linear propagation through scattering plates or MMFs [4]. So far, few works have dealt with the nonlinear propagation regime[5, 6]