Postural Control and Consciousness and Their Applications to Lower-Limb Exoskeletons

Human postural control requires high coordination and is distributed over the whole musculoskeletal and nervous systems. Hence, postural balance can be impaired due to various pathologies. Efficient rehabilitation programs and technological solutions are therefore needed to alleviate the burden due to the risk of falls and lack of mobility. In this thesis, I have sought for solutions to improve postural balance with two different approaches. One approach is based on the application of neuroscience principles, while the other relies on engineering. With the emergence of exergames for balance training, it is essential to understand how the central nervous system integrates augmented visual feedback. Research in motor learning has demonstrated the need of experiencing errors to adapt to the environment and learn new skills. Hence, studies have proposed to visually amplify trajectory errors to promote learning. As this strategy demonstrated promising results for upper limb rehabilitation, I investigated whether visual error augmentation promotes motor adaptation during a balance task. Based on the observer model, I also investigated whether there is a link between sensorimotor learning and a conscious experience of movements known as the sense of agency. Our results suggest that visual error augmentation may promote balance learning and that the optimal gain may be influenced by the sense of agency. Moreover, our results illustrate that humans monitor their actions in an effector-independent manner. Although motor learning is different from neurorehabilitation, these studies help to understand cognitive components of motor learning that are of scientific and clinical relevance. Patients with severe balance deficits need engineering solutions to stand up and walk. We developed a lower-limb exoskeleton, called TWIICE, with the goal to give back autonomy to people with a complete spinal cord injury. Most exoskeletons require that the user manages balance while walking or standing with the help of crutches. To facilitate the interaction with the environment while standing, we developed the first postural controllers enabling patients with complete paraplegia to stand in a low-actuator count exoskeleton without the need for crutches. This could have important implications for the independence of individuals with paraplegia, their inclusion in social activities and their potential inclination to use an exoskeleton on a daily basis for the associated health benefits.