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

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

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

Speed-related spinal excitation from ankle dorsiflexors to knee extensors during human walking

International audienceAutomatic adjustments of muscle activity throughout the body are required for the maintenance of balance during human walking. One mechanism that is likely to contribute to this control is the heteronymous spinal excitation between human ankle dorsiflexors and knee extensors (CPQ-reflex). Here, we investigated the CPQ-reflex at different walking speeds (1-6 km/h) and stride frequencies (0.6-1.3 Hz) in healthy human subjects to provide further evidence of its modulation, and its role in ensuring postural stability during walking. The CPQ-reflex was small or absent at walking speeds below 2-3 km/h, then increased with walking speeds about 3-4 km/h, and reached a plateau without any further change at walking speeds from 4 to 6 km/h. The reflex showed no modulation when the stride cycle was varied at constant speed (4 km/h; short steps versus long steps). These changes were unlikely to be only caused by changes in the background EMG activity and modifications in peripheral input, and likely reflected central modulation of transmission in the involved reflex pathways as well. It is suggested that the purpose of the reflex is to ensure knee stability at moderate-to-high walking speeds

Abnormal cortical brain integration of somatosensory afferents in ALS

International audienceObjectives: Infraclinical sensory alterations have been reported at early stages of amyotrophic lateral sclerosis (ALS). While previous studies mainly focused on early somatosensory evoked potentials (SEPs), late SEPs, which reflect on cortical pathways involved in cognitive-motor functions, are relatively underinvestigated. Early and late SEPs were compared to assess their alterations in ALS.Methods: Median and ulnar nerves were electrically stimulated at the wrist, at 9 times the perceptual threshold, in 21 ALS patients without clinical evidence of sensory deficits, and 21 age- and gender-matched controls. SEPs were recorded at the Erb point using surface electrodes and using a needle inserted in the scalp, in front of the primary somatosensory area (with reference electrode on the ear lobe).Results: Compared to controls, ALS patients showed comparable peripheral (N9) and early cortical component (N20, P25, N30) reductions, while the late cortical components (N60, P100) were more depressed than the early ones.Conclusions: The peripheral sensory alteration likely contributed to late SEP depression to a lesser extent than that of early SEPs

Absence of hyperexcitability of spinal motoneurons in patients with amyotrophic lateral sclerosis

International audienceExperimental models have primarily revealed spinal motoneuron hypoexcitability in amyotrophic lateral sclerosis (ALS), which is contentious considering the role of glutamate-induced excitotoxicity in neurodegeneration and clinical features rather supporting hyperexcitability. This phenomenon was evaluated in human patients by investigating changes in motor unit firing during contraction and relaxation. Twenty-two ALS patients with subtle motor deficits and 28 controls performed tonic contractions of extensor carpi radialis, triceps brachialis, tibialis anterior and quadriceps, aiming to isolate a low-threshold unit (U1) on the electromyogram (EMG). Subsequently, they performed a stronger contraction or tendon vibration was delivered, to recruit higher threshold unit (U2) for 10 s before they relaxed progressively. EMG and motor unit potential analyses suggest altered neuromuscular function in all muscles, including those with normal strength (Medical Research Council score at 5). During the preconditioning tonic phase, U1 discharge frequency did not differ significantly between groups. During recruitment, the increase in U1 frequency (∆F-R) was comparable between groups both during contraction and tendon vibration. During derecruitment, the decrease in U1 frequency (∆F-D) was reduced in ALS regardless of the recruitment mode, particularly for ∆F-R <8 Hz in the upper limbs, consistent with the muscle weakness profile of the group. ∆F-D was associated with functional disability and its reduction was more pronounced in patients with more rapid disease progression rate. This in vivo study has demonstrated reduced motoneuron capacity for self-sustained discharge, and further supports that motoneurons are normo- to hypoexcitable in ALS patients, similar to observations in experimental models

Interrogating Interneurone Function using Threshold Tracking of the H Reflex in Healthy Subjects and Patients with Motor Neurone Disease

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Modulation of recurrent inhibition from knee extensors to ankle motoneurones during human walking

The neural control for muscle coordination during human locomotion involves spinal and supraspinal networks, but little is known about the exact mechanisms implicated. The present study focused on modulation of heteronymous recurrent inhibition from knee extensors to ankle motoneurones at different times in the gait cycle, when quadriceps (Quad) muscle activity overlaps that in tibialis anterior (TA) and soleus (Sol). The effects of femoral nerve stimulation on ankle motoneurones were investigated during treadmill walking and during tonic co-contraction of Quad and TA/Sol while standing. Recurrent inhibition of TA motoneurones depended on the level of background EMG, and was similar during walking and standing for matched background EMG levels. On the other hand, recurrent inhibition in Sol was reduced in early stance, with respect to standing, and enhanced in late stance. Reduced inhibition in Sol was also observed when Quad was coactivated with TA around the time of heel contact, compared to standing at matched background EMG levels in the two muscles. The modulation of recurrent inhibition of Sol during walking might reflect central and/or peripheral control of the Renshaw cells. These modulations could be implicated in the transition phases, from swing to stance to assist Sol activation during the stance phase, and from stance to swing, for its deactivation