Relative Contribution of Proprioceptive and Vestibular Sensory Systems to Locomotion: Opportunities for Discovery in the Age of Molecular Science

Locomotion is a fundamental animal behavior required for survival and has been the subject of neuroscience research for centuries. In terrestrial mammals, the rhythmic and coordinated leg movements during locomotion are controlled by a combination of interconnected neurons in the spinal cord, referred as to the central pattern generator, and sensory feedback from the segmental somatosensory system and supraspinal centers such as the vestibular system. How segmental somatosensory and the vestibular systems work in parallel to enable terrestrial mammals to locomote in a natural environment is still relatively obscure. In this review, we first briefly describe what is known about how the two sensory systems control locomotion and use this information to formulate a hypothesis that the weight of the role of segmental feedback is less important at slower speeds but increases at higher speeds, whereas the weight of the role of vestibular system has the opposite relation. The new avenues presented by the latest developments in molecular sciences using the mouse as the model system allow the direct testing of the hypothesis

Understanding motor control in humans to improve rehabilitation robots

Recent reviews highlighted the limited results of robotic rehabilitation and the low quality of evidences in this field. Despite the worldwide presence of several robotic infrastructures, there is still a lack of knowledge about the capabilities of robotic training effect on the neural control of movement. To fill this gap, a step back to motor neuroscience is needed: the understanding how the brain works in the generation of movements, how it adapts to changes and how it acquires new motor skills is fundamental. This is the rationale behind my PhD project and the contents of this thesis: all the studies included in fact examined changes in motor control due to different destabilizing conditions, ranging from external perturbations, to self-generated disturbances, to pathological conditions. Data on healthy and impaired adults have been collected and quantitative and objective information about kinematics, dynamics, performance and learning were obtained for the investigation of motor control and skill learning. Results on subjects with cervical dystonia show how important assessment is: possibly adequate treatments are missing because the physiological and pathological mechanisms underlying sensorimotor control are not routinely addressed in clinical practice. These results showed how sensory function is crucial for motor control. The relevance of proprioception in motor control and learning is evident also in a second study. This study, performed on healthy subjects, showed that stiffness control is associated with worse robustness to external perturbations and worse learning, which can be attributed to the lower sensitiveness while moving or co-activating. On the other hand, we found that the combination of higher reliance on proprioception with \u201cdisturbance training\u201d is able to lead to a better learning and better robustness. This is in line with recent findings showing that variability may facilitate learning and thus can be exploited for sensorimotor recovery. Based on these results, in a third study, we asked participants to use the more robust and efficient strategy in order to investigate the control policies used to reject disturbances. We found that control is non-linear and we associated this non-linearity with intermittent control. As the name says, intermittent control is characterized by open loop intervals, in which movements are not actively controlled. We exploited the intermittent control paradigm for other two modeling studies. In these studies we have shown how robust is this model, evaluating it in two complex situations, the coordination of two joints for postural balance and the coordination of two different balancing tasks. It is an intriguing issue, to be addressed in future studies, to consider how learning affects intermittency and how this can be exploited to enhance learning or recovery. The approach, that can exploit the results of this thesis, is the computational neurorehabilitation, which mathematically models the mechanisms underlying the rehabilitation process, with the aim of optimizing the individual treatment of patients. Integrating models of sensorimotor control during robotic neurorehabilitation, might lead to robots that are fully adaptable to the level of impairment of the patient and able to change their behavior accordingly to the patient\u2019s intention. This is one of the goals for the development of rehabilitation robotics and in particular of Wristbot, our robot for wrist rehabilitation: combining proper assessment and training protocols, based on motor control paradigms, will maximize robotic rehabilitation effects

Les réponses des membres inférieurs à des translations médio-latérales imprévues pendant le mouvement de pédalage

Les perturbations vers la gauche ou vers la droite sont des occurrences quasi-quotidiennes pour un bon nombre de gens. Se faire bousculer en marchant dans la foule ou subir les effets inertiels d'un véhicule de transport en commun tournant ou s'arrêtant soudainement ne sont que deux exemples communs de telles situations. De plus, les perturbations dues aux glissements latéraux sont fréquemment observées chez les personnes âgées. Les articulations des membres inférieurs et du tronc ont moins de latitude de mouvement dans le plan frontal que dans le plan sagittal. En conséquence, lors d'une translation médio-latérale inattendue le système nerveux central (SNC) utilise probablement des stratégies compensatoires différentes du cas de la direction antéro-postérieure. Le but de cette étude était d'évaluer les stratégies compensatoires utilisées lors de perturbations perpendiculaires au plan du mouvement. Un vélo ergométrique modifié fut utilisé comme modèle de mouvements rythmiques; dans une telle situation, les effets de l'équilibre sont de beaucoup amoindris et les réactions compensatoires peuvent être attribuées à la perturbation du mouvement rythmique. Pour les fins de cette étude les sujets eurent à pédaler sous quatre conditions expérimentales différentes: dynamique active (DA), au cours de laquelle les sujets pédalaient à une fréquence de 1 Hz maintenue à l'aide d'un métronome et d'information présentée sur un écran d'ordinateur; dynamique passive (DP), au cours de laquelle les mouvements enregistrés sous la condition DA étaient reproduits à l'aide d'un moteur dynamométrique tandis que les sujets devaient simplement relaxer; statique active (SA), au cours de laquelle chaque sujet devait essayer de reproduire l'activité musculaire produite par leur soléaire sous la condition DA; statique passive (SP), au cours de laquelle les sujets devaient simplement maintenir chacune des positions du cycle de pédalage tout en relaxant. Des mouvements vers la gauche et vers la droite d'à peu près 1 g (9.8 ms-2) d'accélération furent appliqués aléatoirement à l'aide d'un cylindre électrique pendant une des quatre phases du cycle de pédalage: propulsion (P), récupération (R), transition PR, et transition RP. L'activité électromyographique (EMG) du soléaire (SOL), du médial du gastrocnémien (MG), du tibial antérieur (TA), du vaste latéral (VL), du biceps fémoral [chef court] (BF), et du tenseur du fascia lata (TFL) furent enregistrés et analysés. Les réponses EMG furent divisées en deux époques (E) selon la latence de la réponse:

Functional organization of cutaneous reflex pathways during locomotion and reorganization following peripheral nerve and/or spinal cord lesions

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

The role of inter-enlargement propriospinal neurons in locomotion following spinal cord injury.

The focus of this dissertation is to explore the functional role of two anatomically-defined pathways in the adult rat spinal cord before and after spinal cord injury (SCI). To do this, a TetOn dual virus system was used to selectively and reversibly silence neurons with cell bodies at spinal segment L2 and projections to spinal segment C6 (long ascending propriospinal neurons, LAPNs) and neurons that originate in the C6 spinal segment and terminate at L2 spinal segment (long descending propriospinal neurons, LDPNs). This dissertation is divided into five chapters. Chapter One provides background information regarding spinal cord injury, locomotion, and a brief introduction to propriospinal neurons. Chapter Two details the functional consequences of silencing LAPNs and LDPNs in uninjured animals, with specific regard to sensory context during overground locomotion. Chapter Three describes the consequences of silencing LAPNs following a mild/moderate spinal cord contusion injury. Spinal cord injury (SCI) fundamentally affects the ability to maintain patterned weight-supported stepping. Chapter Four focuses on the functional outcomes of silencing the reciprocal descending inter-enlargement pathway, LDPNs, after mild/moderate spinal cord contusion injury. Finally, Chapter Five compares the differential roles of LAPNs and LDPNs in left-right coordination prior to injury, especially in a sensory context-dependent manner. A section of this chapter is devoted to a recap of injured data for both LAPN and LDPN silencing post-injury and attempts to place this work in context with other studies whose focus is on propriospinal pathways after SCI

A Haptic Feedback System for Lower Limb Amputees Based on Gait Event Detection

Lower limb amputation has significant effects on a person’s quality of life and ability to perform activities of daily living. Prescription of prosthetic device post amputation aims to help restore some degrees of mobility function, however studies have shown evidence of low balance confidence and higher risk of falling among amputee community, especially those suffering from above knee amputation. While advanced prostheses offer better control, they often lack a form of feedback that delivers the awareness of the limb position to the prosthetic user while walking. This research presents the development and evaluation of a wearable skinstretch haptic feedback system intended to deliver cues of two crucial gait events, namely the Initial Contact (IC) and Toe-off (TO) to its wearer. The system comprises a haptic module that applies lateral skin-stretch on the upper leg or the trunk, corresponding to the gait event detection module based on Inertial Measurement Unit (IMU) attached at the shank. The design and development iterations of the haptic module is presented, and characterization of the feedback parameters is discussed. The validation of the gait event detection module is carried out and finally the integration of the haptic feedback system is described. Experimental work with healthy subjects and an amputee indicated good perceptibility of the feedback during static and dynamic (walking) condition, although higher magnitude of stretch was required to perceive the feedback during dynamic condition. User response time during dynamic activity showed that the haptic feedback system is suitable for delivering cues of IC and TO within the duration of the stance phase. In addition, feedback delivered in discernible patterns can be learned and adapted by the subjects. Finally, a case study was carried out with an above-knee amputee to assess the effects of the haptic feedback on spatio-temporal gait parameters and on the vertical ground reaction force during treadmill and overground walking. The research presented in this report introduces a novel design of a haptic feedback device. As such, the outcome includes a well-controlled skin-stretch effect which contributes to the research by investigating skin-stretch feedback for conveying discrete event information rather than conveying direction information as presented in other studies. In addition, it is found that stretch magnitude as small as 3 mm could be perceived in short duration of 150 ms during dynamic condition, making it a suitable alternative to other widely investigated haptic modality such as vibration for ambulatory feedback application. With continuous training, the haptic feedback system could possibly benefit lower limb amputees by creating awareness of the limb placement during ambulation, potentially reducing visual dependency and increasing walking confidence