Repetitive transcranial magnetic stimulation and transcranial direct current stimulation in motor rehabilitation after stroke: An update

AbstractStroke is a leading cause of adult motor disability. The number of stroke survivors is increasing in industrialized countries, and despite available treatments used in rehabilitation, the recovery of motor functions after stroke is often incomplete. Studies in the 1980s showed that non-invasive brain stimulation (mainly repetitive transcranial magnetic stimulation [rTMS] and transcranial direct current stimulation [tDCS]) could modulate cortical excitability and induce plasticity in healthy humans. These findings have opened the way to the therapeutic use of the 2 techniques for stroke. The mechanisms underlying the cortical effect of rTMS and tDCS differ. This paper summarizes data obtained in healthy subjects and gives a general review of the use of rTMS and tDCS in stroke patients with altered motor functions. From 1988 to 2012, approximately 1400 publications were devoted to the study of non-invasive brain stimulation in humans. However, for stroke patients with limb motor deficit, only 141 publications have been devoted to the effects of rTMS and 132 to those of tDCS. The Cochrane review devoted to the effects of rTMS found 19 randomized controlled trials involving 588 patients, and that devoted to tDCS found 18 randomized controlled trials involving 450 patients. Without doubt, rTMS and tDCS contribute to physiological and pathophysiological studies in motor control. However, despite the increasing number of studies devoted to the possible therapeutic use of non-invasive brain stimulation to improve motor recovery after stroke, further studies will be necessary to specify their use in rehabilitation

Effects of Hand Configuration on the Grasping, Holding, and Placement of an Instrumented Object in Patients With Hemiparesis

Objective: Limitations with manual dexterity are an important problem for patients suffering from hemiparesis post stroke. Sensorimotor deficits, compensatory strategies and the use of alternative grasping configurations may influence the efficiency of prehensile motor behavior. The aim of the present study is to examine how different grasp configurations affect patient ability to regulate both grip forces and object orientation when lifting, holding and placing an object.Methods: Twelve stroke patients with mild to moderate hemiparesis were recruited. Each was required to lift, hold and replace an instrumented object. Four different grasp configurations were tested on both the hemiparetic and less affected arms. Load cells from each of the 6 faces of the instrumented object and an integrated inertial measurement unit were used to extract data regarding the timing of unloading/loading phases, regulation of grip forces, and object orientation throughout the task.Results: Grip forces were greatest when using a palmar-digital grasp and lowest when using a top grasp. The time delay between peak acceleration and maximum grip force was also greatest for palmar-digital grasp and lowest for the top grasp. Use of the hemiparetic arm was associated with increased duration of the unloading phase and greater difficulty with maintaining the vertical orientation of the object at the transitions to object lifting and object placement. The occurrence of touch and push errors at the onset of grasp varied according to both grasp configuration and use of the hemiparetic arm.Conclusion: Stroke patients exhibit impairments in the scale and temporal precision of grip force adjustments and reduced ability to maintain object orientation with various grasp configurations using the hemiparetic arm. Nonetheless, the timing and magnitude of grip force adjustments may be facilitated using a top grasp configuration. Conversely, whole hand prehension strategies compound difficulties with grip force scaling and inhibit the synchrony of grasp onset and object release

Development of Electrically Conductive Thermoplastic Composites for Bipolar Plate Application in Polymer Electrolyte Membrane Fuel Cell

Polymer electrolyte membrane fuel cells (PEMFCs) have the potential to play a major role as energy generators for transportation and portable applications. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically the bipolar plates. One approach to preparing PEMFCs for commercialization is to develop new bipolar plate materials, related to mass production of fuel cells. Thermoplastic/carbon filler composites with low filler loading have a major advantage in that they can be produced by a conventional low-cost injection molding technique. In addition, the materials used are inexpensive, easy to shape, and lightweight. An optimal bipolar plate must possess high surface and bulk electronic conductivity, sufficient mechanical integrity, low permeability, and corrosion resistance. However, it is difficult to achieve high electrical conductivity from a low-cost thermoplastic composite with low conductive filler loading. Concerns over electrical conductivity improvement and the injection processability of composites have brought forth the idea of producing a polypropylene/three-carbon-filler composite for bipolar plate application. The thesis addresses the development of synergistic effects of filler combinations, investigating composite conductive materials and using composite bipolar plate testing in PEMFCs. One significant effect of conductive network formation is the synergetic effects of different carbon filler sizes, shapes, and multiple filler ratios on the electrical conductivity of bipolar plate materials. A polypropylene resin combined with low-cost conductive fillers (graphite, conductive carbon black, and carbon fibers with 55 wt% of filler loading) compose the main composite for all investigations in this research. Numerous composite formulations, based on single-, two-, and three-filler systems, have been created to investigate the characteristics and synergistic effects of multiple fillers on composite conductivity. Electrical conductivity measurements corresponding to PEMFC performance and processing characteristics were investigated. Experimental work also involved other ex-situ testing for the physical requirements of commercial bipolar plates. All combinations of fillers were found to have a significant synergistic effect that increased the composite electrical conductivity. Carbon black was found to have the highest influence on the increase of electrical conductivity compared to the other fillers. The use of conjugated conducting polymers such as polypyrrole (PPy) to help the composite blends gain desirable conductivities was also studied. Electrical conductivity was significantly improved conductivity by enriching the conducting paths on the interfaces between fillers and the PP matrix with PPy. The conductive network was found to have a linkage of carbon fibers following the respective size distributions of fibers. The combination of Fortafil and Asbury carbon fiber mixture ameliorated the structure of conductive paths, especially in the through-plane direction. However, using small fibers such as carbon nanofibers did not significantly improve in electrical conductivity. The useful characteristics of an individual filler and filler supportive functions were combined to create a novel formula that significantly improved electrical conductivity. Other properties, such as mechanical and rheological ones, demonstrate the potential to use the composites in bipolar plate applications. This research contributes a direction for further improvement of marketable thermoplastic bipolar plate composite materials

Stimulation magnétique transcrânienne et inhibition intra-corticale (variabilité liée au recrutement des motoneurones spinaux et des neurones corticaux)

L activation "transynaptique" des neurones pyramidaux du cortex moteur primaire par stimulation magnétique transcrânienne (TMS) induit des volées corticospinales (CSP) transmises aux motoneurones spinaux. Leur activation entraîne une contraction traduite par un potentiel (PEM) dans l activité électromyographique du muscle cible. L amplitude du PEM en mV sert à évaluer l état d excitabilité des neurones de la voie CSP. Si une TMS conditionnante précède de 2 à 5 ms une TMS test, le PEM évoqué par le double choc de TMS est plus petit que le PEM induit par la TMS test seule. Cette inhibition, la SICI, vient de l activation d interneurones inhibiteurs qui modifient la réponse des neurones pyramidaux à la TMS test. La variabilité des résultats remet en cause la fiabilité de cette méthode. Plusieurs paramètres ont été testés, mais jamais les propriétés des neurones corticaux et spinaux n ont été suspectées. L objectif du projet doctoral était de vérifier si les propriétés de ces neurones influencent l évaluation de la SICI chez l Homme. Le PEM test a été exprimé en % de la réponse motrice maximale (Mmax), plutôt qu en mV, pour évaluer la fraction de MNs recrutés par la TMS test. Des unités motrices isolées ont été testées pour explorer les réponses des neurones corticaux à la TMS. Les résultats ont révélé que i) la sommation des volées CSP au niveau des MNs n est pas linéaire ce qui influence l évaluation de la SICI, ii) l intégration des entrées synaptiques inhibitrices au niveau des réseaux corticaux afférents aux cellules pyramidales n est pas linéaire. Ce travail a permis de proposer une nouvelle méthode d évaluation des mécanismes corticaux révélés avec la TMS.PARIS-BIUP (751062107) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Interactions entre la commande motrice descendante et les afférences proprioceptives et cutanées sur les interneurones spinaux au cours du mouvement chez l'homme

Un mouvement résulte de l activation séquentielle et coordonnée de groupes musculaires agissant sur diverses articulations. Pour le réaliser, un programme moteur est alors élaboré au niveau du système nerveux central et peut être ajusté selon les conditions environnementales pour une exécution harmonieuse. Des intégrations sensori-motrices ont lieu au niveau des interneurones spinaux, cibles des afférences périphériques et de la commande corticale. De nombreux réseaux spinaux alimentés par les afférences proprioceptives et cutanées interviennent donc dans le contrôle de mouvements pluri-articulaires et impliquent notamment des interneurones propriospinaux. Le but de cette thèse a été d explorer le rôle de certains de ces circuits spinaux. Il est montré que l excitabilité de ces circuits est renforcée lors de mouvements volontaires réalisés avec un but par rapport à des contractions toniques isolées ou un contexte passif. Les résultats renforcent l hypothèse selon laquelle les réflexes spinaux explorés sont le support des synergies musculaires mises en jeu lors de ces mouvements. Les modulations d excitabilité de ces réflexes seraient liées à des modifications du contrôle exercé par les structures supraspinales sur les interneurones transmettant ces réflexes ou à des modifications des propriétés intrinsèques des réseaux spinaux.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Modulation of heteronymous reflexes from ankle dorsiflexors to hamstring muscles during human walking

In 16 human subjects, stimulation of the common peroneal nerve (CPN) was applied during walking and standing. The effect of the stimulation was evaluated from the rectified and averaged biceps femoris (BF) electromyographic (EMG) activity. In the swing phase of walking, the CPN stimulation evoked a suppression in the BF EMG in 12 of the subjects. In the early stance phase, the suppression was replaced by facilitation at a similar latency in 9 of the subjects. Of the other 3 subjects, in whom a suppression was observed during swing, a decrease in the suppression was observed in the stance phase in two of them. During a voluntary co-contraction of BF and tibialis anterior while standing, a suppression similar to that observed in the swing phase was observed. The thresholds of the suppression and facilitation were identical, suggesting that afferents of similar diameter were responsible. Cutaneous stimuli, which mimicked the sensation evoked by the CPN stimulation, but without activation of muscle afferents, did not produce similar effects in the BF EMG activity. It is suggested that the observed response and reflex reversal may reflect opening of an excitatory group I pathway in the early stance phase of walking with a concomitant shut-down of heteronymous group I inhibition

Contrôle cortico-spinal à partir des aires motrices et pré-motrices impliquant le système propriospinal cervical chez l'Homme

Les neurones propriospinaux C3-C4, situés au niveau des cervicales C3-C4, sont connectés de façon excitatrice ou inhibitrice aux motoneurones des membres supérieurs. Ils reçoivent des signaux périphériques et descendants, communiquent avec de multiples interneurones de la moelle et envoient une copie de leurs efférences au cervelet. Les neurones propriospinaux excitateurs sont sous le contrôle d interneurones inhibiteurs. Les neurones propriospinaux pourraient servir à assister les commandes motrices provenant de structures supérieures, ainsi que l initiation et la terminaison du mouvement. Des études comportementales chez l animal ont montré que ce système influence particulièrement les mouvements d atteinte de cible visuellement guidés du membre antérieur (reaching), ainsi que des mouvements de préhension demandant de la dextérité (precision grip). Le but de cette thèse est de confirmer le rôle du système propriospinal dans la transmission de la commande motrice du bras chez l Homme. Ce travail a été divisé en deux parties. Dans la première partie, nous avons étudié les effets d une activation du système propriospinal sur la contraction d un muscle fléchisseur du poignet (FCR) au cours de tâches dynamiques et visuo-guidées du bras et de la main (reach to grasp et reach to point). Nous avons activé les neurones propriospinaux à l aide de stimulations magnétiques transcraniennes (TMS) et de stimulations électriques du nerf ulnaire, pour en observer les effets sur la contraction musculaire du FCR au cours des différentes tâches. Nous avons montré que le système propriospinal facilitait la contraction du FCR lors du reach to grasp mais pas lors du reach to point. Nous avons aussi montré que durant le reach to grasp, la facilitation propriospinale n avait lieu que durant la phase de reaching mais pas pendant la phase de grasping. En augmentant l intensité de stimulation du nerf ulnaire, la facilitation disparaissait. Nous avons émis l hypothèse que cette différence de facilitation propriospinale entre les différentes tâches et entre les différentes phases du mouvement soit due à une différence de retours proprioceptifs ainsi qu à une différence de commandes descendantes. Nous avons suggéré que le contrôle des neurones propriospinaux diffère selon que la tâche soit statique (levée d inhibition feedback) ou dynamique (renforcement de la commande descendante sur les neurones propriospinaux). Nous avons proposé que le système propriospinal soit un élément important pour l expression de la dextérité en aidant notamment la stabilisation du bras. La seconde partie consistait à mettre en évidence l existence d une relation entre les neurones propriospinaux inhibiteurs et le cortex moteur primaire (M1) et le cortex pré-moteur ventral (PMv). Pour cela, nous avons réalisé des expériences de convergence de volées sur les neurones propriospinaux inhibiteurs à l aide de stimulations électriques du nerf médian et de TMS appliquée sur M1 ou PMv. Nous avons réussi à démontrer l existence d une interaction entre PMv et les neurones propriospinaux inhibiteurs, mais pas entre ces neurones et M1. Cette interaction pourrait se faire par des projections cortico-spinales issues de PMv ou en passant par M1. Nous avons donc inhibé transitoirement M1 par un traitement de double continuous theta burst tout en testant les interactions entre PMv et les neurones propriospinaux inhibiteurs. Les données préliminaires montrent que l interaction avec PMv subsiste toujours : il est possible que des projections cortico-spinales issues du PMv projette (directement ou indirectement) sur les neurones propriospinaux inhibiteurs.The C3-C4 propriospinal neurons, located at the C3-C4 spinal levels, has excitatory and inhibitory connections to arm motoneurons. They receive descending and peripheral inputs, communicate with multiple spinal interneurons and send an efferent copy to the cerebellum. The excitatory propriospinal neurons are under the control of spinal inhibitory interneurons. The propriospinal neurons could assist the motor command displayed by suprasegmental structures and could also assist the beginning and the ending of movement. Behavior studies in animals, have shown that reaching movement and precision grip are influenced by this system. The aim of this thesis is to confirm the function of the propriospinal system into arm motor command transmission in human. This work has been divided in two parts. In the first part, we have studied in human the effects of an activation of the propriospinal system on the wrist flexor (FCR) muscle contraction during reach to grasp and reach to point. In order to see the effect of the propriospinal neurons on muscular contraction during different tasks, propriospinal neurons were activated with transcranial magnetic stimulations (TMS) and ulnar nerve electrical stimulation. We have shown that FCR muscular contraction was facilitated during reach to grasp but not during reach to point. We have also shown that during reach to grasp, the reaching phase was facilitated by propriospinal neurons, but not the grasping phase. By increasing the intensity of the median nerve stimulation, propriospinal facilitation disappeared. We hypothesized that this difference in propriospinal facilitation between the different tasks and movement phases, originated from a difference of propriosceptive feedbacks and descending inputs. We have also suggested that propriospinal neurons control was different depending on whether the task is static (feedback inhibition removal) or dynamic (reinforcement of the descending inputs on propriospinal neurons). We suggest that the propriospinal system could assist dexterity by stabilizing the arm. In the second part, we have shown that inhibitor propriospinal neurons and ventral premotor cortex (vPM) or primary motor cortex (M1) interact.We made descending and peripheral volleys to converge on the inhibitor propriospinal neurons by using TMS and median nerve electrical stimulation. According to our results, there is an interaction between inhibitor propriospinal neurons and the vPM but not between propriospinal neurons and M1. This interaction may imply cortico-spinal inputs from vPM or by passing through M1. Thus, we have inhibited transitorily M1 synaptic transmissions by using paired continuous theta burst while testing interaction between inhibitor propriospinal neurons and vPM. Preliminary data have shown that despite inhibition of M1, interaction between vPM and inhibitor propriospinal neurons still exists : it might be that cortico-spinal inputs projects (directly or not) from vPM onto inhibitor propriospinal neuronsPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF