Section: Overall Objectives
Functional Electrical Stimulation (FES) has been used for about 30 years in order to restore movements. At the beginning, only surface stimulation was possible and thus only used in a clinical context due to the low reliability of electrode placements. In the early eighties, implanted FES appeared through well known applications (pacemaker, Brindley bowel control, cochlear implant, and more recently Deep Brain Stimulation). The complexity of the system for movement restoration is such that no commercial application really arise. Even though the original idea of FES is still the same, activating the moto-neurone axons with impulse current generator, the stimulus waveform and its parameters have drastically evolved and the electrode placements became various: epimysial stimulation at the muscle's motor point, neural stimulation on the nerve, Sacral roots stimulation near the spinal cord. These changes came from fundamental research, not yet achieved, in neurophysiology. This knowledge can efficiently be included in the next implanted neuroprosthetic devices allowing a wide variety of features. Moreover, currently, FES is the only way to restore motor function even though biological solutions are studied, because the research are not yet successfully tested on humans. Few teams carry out researches on implanted FES ( http://www.ifess.org ) and the functional results remain poor. Nevertheless, the technique has proved to be useable and needs enhancements that will be addressed by DEMAR (Deambulation Et Mouvement ARtificiel). In particular, complex electrode geometries associated with complex stimulus waveforms provide a way to perform fibre type selectivity and spatial localisation of the stimuli in the nerves. These features are not yet implemented and demand new hardware and software architectures. Some teams in Denmark (Thomas Sinkjaer, SMI U. Aalborg), Germany (Klaus Peter Koch, IBMT Franhaufer Institute), England (Nick Donaldson, U. College of London), Belgium (Claude Veraart, U. Catholique de Louvain), United States (Thomas Mortimer, Cleveland FES centre), and Canada (Mohammad Sawan, Ecole Polytechnique de Montréal), work on multi-polar neural stimulation but mainly on the electrode aspect.
Such a complex system needs advanced control theory tools coupled with a deep understanding of the underlying neurophysiological processes. This major area of research will be also an important part of the DEMAR objectives. Very few teams (for instance Robert Riener, ETH in Zurich, Switzerland) work on this topic because it needs a great amount of interactions between completely different disciplines such as neurophysiology, biomechanics, automatic control theory, and advanced signal processing. Besides, animal experiments performed in order to validate and identify models are particularly difficult to manage. Control schemes on such a complex non linear, under-actuated system, not completely observed and perturbed by the voluntary movements of the patient are quite difficult to study due to the lack of precise simulations platforms (for practical evaluation before experimentation) and the lack of theoretical results on such systems.
DEMAR (DEambulation et Mouvement ARtificiel) is a joint project between INRIA, CNRS, Universities of Montpellier I and II. DEMAR is located at LIRMM (joint CNRS and University laboratory working on Computer sciences, Micro electronics, and Robotics) in Montpellier. DEMAR works in close relationship with rehabilitation centres among them the Centre Bouffard Vercelli in Cerbère and Propara in Montpellier. International collaborations exist since 2003 with the Sensory Motor Interaction Lab at the University of Aalborg in Denmark (Professors Thomas Sinkjaer, Dejan Popovic, Ken Yoshida). DEMAR research interests are centered on the human sensory motor system, including muscles, sensory feedbacks, and neural motor networks. Indeed, DEMAR focuses on two global axes of research:
Modelling and controlling the human sensory motor system.
Interfacing artificial and natural parts through implanted neuroprosthetic devices.
The main applied research fields are then:
Quantitative characterization of the human sensory motor system firstly for motor disorders diagnosis and objective quantification, and secondly in order to help the design of neuroprosthetic devices.
Restoring motor and sensitive functions through implanted functional electrical stimulation (FES) and neural signals sensing.