Revisiting the Body-Schema Concept in the Context of Whole-Body Postural-Focal Dynamics

The body-schema concept is revisited in the context of embodied cognition, further developing the theory formulated by Marc Jeannerod that the motor system is part of a simulation network related to action, whose function is not only to shape the motor system for preparing an action (either overt or covert) but also to provide the self with information on the feasibility and the meaning of potential actions. The proposed computational formulation is based on a dynamical system approach, which is linked to an extension of the equilibrium-point hypothesis, called Passive Motor Paradigm: this dynamical system generates goal-oriented, spatio-temporal, sensorimotor patterns, integrating a direct and inverse internal model in a multi-referential framework. The purpose of such computational model is to operate at the same time as a general synergy formation machinery for planning whole-body actions in humanoid robots and/or for predicting coordinated sensory–motor patterns in human movements. In order to illustrate the computational approach, the integration of simultaneous, even partially conflicting tasks will be analyzed in some detail with regard to postural-focal dynamics, which can be defined as the fusion of a focal task, namely reaching a target with the whole-body, and a postural task, namely maintaining overall stability

Passive Motion Paradigm: An Alternative to Optimal Control

In the last years, optimal control theory (OCT) has emerged as the leading approach for investigating neural control of movement and motor cognition for two complementary research lines: behavioral neuroscience and humanoid robotics. In both cases, there are general problems that need to be addressed, such as the “degrees of freedom (DoFs) problem,” the common core of production, observation, reasoning, and learning of “actions.” OCT, directly derived from engineering design techniques of control systems quantifies task goals as “cost functions” and uses the sophisticated formal tools of optimal control to obtain desired behavior (and predictions). We propose an alternative “softer” approach passive motion paradigm (PMP) that we believe is closer to the biomechanics and cybernetics of action. The basic idea is that actions (overt as well as covert) are the consequences of an internal simulation process that “animates” the body schema with the attractor dynamics of force fields induced by the goal and task-specific constraints. This internal simulation offers the brain a way to dynamically link motor redundancy with task-oriented constraints “at runtime,” hence solving the “DoFs problem” without explicit kinematic inversion and cost function computation. We argue that the function of such computational machinery is not only restricted to shaping motor output during action execution but also to provide the self with information on the feasibility, consequence, understanding and meaning of “potential actions.” In this sense, taking into account recent developments in neuroscience (motor imagery, simulation theory of covert actions, mirror neuron system) and in embodied robotics, PMP offers a novel framework for understanding motor cognition that goes beyond the engineering control paradigm provided by OCT. Therefore, the paper is at the same time a review of the PMP rationale, as a computational theory, and a perspective presentation of how to develop it for designing better cognitive architectures

Robust muscle synergies for postural control

The musculoskeletal structure of the human and animal body provides multiple solutions for performing any single motor behavior. The long-term goal of the work presented here is to determine the neuromechanical strategies used by the nervous system to appropriately coordinate muscles in order to achieve the performance of daily motor tasks. The overall hypothesis is that the nervous system simplifies muscle coordination by the flexible activation of muscle synergies, defined as a group of muscles activated as a unit, that perform task-level biomechanical functions. To test this hypothesis we investigated whether muscle synergies can be robustly used as building blocks for constructing the spatiotemporal muscle coordination patterns in human and feline postural control under a variety of biomechanical contexts. We demonstrated the generality and robustness of muscle synergies as a simplification strategy for both human and animal postural control. A few robust muscle synergies were able to reproduce the spatial and temporal variability in human and cat postural responses, regardless of stance configuration and perturbation type. In addition inter-trial variability in human postural responses was also accounted for by these muscle synergies. Finally, the activation of each muscle synergy in cat produced a specific stabilizing force vector, suggesting that muscle synergies control task-level variables. The identified muscle synergies may represent general modules of motor output underlying muscle coordination in posture that can be activated in different sensory contexts to achieve different postural goals. Therefore muscle synergies represents a simplifying mechanism for muscle coordination in natural behaviors not only because it is a strategy for reducing the number of variables to be controlled, but because it represents a mechanism for simply controlling multi-segmental task-level variables.Ph.D.Committee Chair: Ting, Lena H.; Committee Member: Chang, Young-Hui; Committee Member: Lee, Robert H.; Committee Member: Nichols, T. Richard; Committee Member: Wolf, Steve L

Analysis of the backpack loading efects on the human gait

Gait is a simple activity of daily life and one of the main abilities of the human being. Often during leisure, labour and sports activities, loads are carried over (e.g. backpack) during gait. These circumstantial loads can generate instability and increase biomechanicalstress over the human tissues and systems, especially on the locomotor, balance and postural regulation systems. According to Wearing (2006), subjects that carry a transitory or intermittent load will be able to find relatively efficient solutions to compensate its effects.info:eu-repo/semantics/publishedVersio

Finite element simulation of the healthy and degenerated lumbar spine : interplay between muscle activity and intervertebral disc multiphysics

The human spine provides mechanical support to the trunk while it protects the spinal cord and nerves from the external loads transferred during daily activities. Such loads are largely controlled by the spine muscles and influence the biophysical regulation of the intervertebral discs (IVD). Numerical models have been important tools for the translation of the external forces into internal loads that otherwise cannot be easily measured directly. This PhD thesis used the predictive ability of constitutive equations to reflect the mechanical properties of the lumbar IVD and muscles and explore the IVD-muscle interplay on the healthy and degenerated spine. A review of the state-of-the-art reported for the estimation of spine loads was performed, and the Hill¿s mus cle model and the poro-hyperelastic formulations used for IVD modeling were particularly detailed. A new constitutive equation assembly was proposed involving one active parameter controlled via strain-based criteria, and four passive parameters. For the latters, literature-based values were initially defined, and a parametric study was designed for the active parameter by proposing stretch-related activation thresholds. An optimization scheme was then developed to define a full set of calibrated values per fascicle using force estimations from a reported rigid body model based on measured kinematics of the vertebrae. To test the robustness of the method, a generic L3-S1 finite element (FE) model was developed that included 46 muscle fascicles and all passive issues. Simulation of forward flexion showed that the predicted muscle forces increased in caudal direction. The intradiscal pressure (IDP) predictions correlated with previous in vivo measurements showing the ability of the model to capture realistic internal loads. To simulate standing, the gravity loads were defined by considering the heterogeneous distribution of body volumes along the trunk. This simulation was also coupled to a previous 8-hour free IVD swelling to mimic the overnight disc hydration. Disc swelling led to muscle activation and force distributions that seemed particularly appropriate to counterbalance the gravity loads, pointing out the likely existence of a functional balance between stretch-induced muscle activation and IVD multiphysics. A geometrical extension was then performed to incorporate all relevant tissues of the full lumbar spine including in total 96 fascicles. The effect of previous rest (PR) and muscle presence (MS) on internal loads was explored in standing and lying. Muscle force predictions in standing showed that with PR, the total loads transferred were altered from compressive to tensile. Overnight, the computed IDP increase reproduced previous in vivo data. Both PR and MS affected the vertebrae motion particularly between L1-L2. When degenerated discs properties were used, a general IDP decrease and up to 14 times higher activation was predicted in standing with PR.At last, the previous workflow was repeated using a patient L1-S1 FE model with patient-specific (P-SP) and condition-depended material properties. In standing, asymmetric fascicle activation with increased shortening at the left side and lateral bending was predicted. The decreased swelling capacity of the degenerated discs was associated to an increased muscle activation needed to balance the gravity loads that tended to flex forward the trunk. Comparisons of the IDP results in both models with healthy discs showed that introducing P-SP geometries gave better correlations with in vivo data. Given the difficulties to evaluate the predicted muscle forces experimentally, such outcome further contributed to the validation of the method. Despite its limitations, this approach allowed to explicitly and rationally explore the interactions between muscle function and passive tissue biomechanics in the lumbar spine. The information provided could help clinical decision for patients whom source of back pain is unclearLa columna vertebral proporciona suport mecànic al tors alhora que protegeix la medul·la espinal i els nervis de les forces externes transferides durant les activitats diàries. Aquestes forces són controlades en gran part pels músculs espinals i influeixen en la regulació biofísica dels discos intervertebrals (IVD).Els models numèrics han estat eines importants per a la traducció de les forces externes en càrregues internes que d'altra manera no poden ser fàcilment mesurades directament.Aquesta tesi utilitza la capacitat predictiva de les equacions constitutives per considerar les propietats mecàniques dels discs lumbars i dels músculs i explorar la interacció IVD-múscul a la columna vertebral sana i degenerada. Es va realitzar una revisió de l'estat de l'art dels mètodes reportats per l'estimació de les càrregues, i es van detallar particularment el model muscular de Hill i les formulacions poro-hiperelàstics utilitzades per a la modelització del disc. Es va proposar un model novedós d'equacions cons titutives implicant un paràmetre actiu controlat a través de criteris basats en la deformació, i quatre paràmetres passius. Per aquests últims, es van definir uns valors inicialment basats en la literatura, mentre que pel paràmetre actiu es va realitzar un estudi paramètric per proposar els llindars d'activació relacionats amb l'estirament.A continuació,es va desenvolupar un esquema d'optimització per definir un conjunt complet de valors calibrats per fascicle utilitzant estimacions de forces d'un model de cos rígid de la literatura basat en la cinemàtica de les vèrtebres mesurada. Per comprovar la robustesa del mètode, es va desenvolupar un model L3-S1 d'elements finits (FE) incloent 46 fascicles musculars i tots els teixits passius. La simulació de flexió anterior va mostrar que les forces musculars predites van augmentar en direcció caudal. Les prediccions de pressió intradiscal (IDP) es van correlacionar amb mesures "in vivo" mostrant així la capacitat del model per capturar les càrregues internes reals.Per simular la posició dempeus , les càrregues de gravetat es van definir considerant la distribució heterogènia dels volums del cos al llarg del tronc. A més, aquesta simulació es va acoblar amb un inflament previ del IVD de 8 hores per imitar la hidratació del disc durant la nit. L'inflament del disc va induir activació muscular i una distribució de forces que semblaven particularment apropiades per a contrarestar les càrregues de gravetat, assenyalant la probable existència d'un equilibri funcional entre l'activació muscular i la multifísica del disc. Després es va realitzar una extensió geomètrica del model per incorporar tots els teixits pertinents de la columna lumbar completa incloent un total de 94 fascicles. L'efecte del repòs previ (PR) i la presència de múscul (MS) sobre les càrregues internes va ser explorat en posició dempeus i es tirada. Durant la nit, l'augment de l'IDP computat va confirmar dades anteriors "in vivo". Quan es van definir propietats degenerades als discs, es va predir una disminució general de l'IDP i una activació fins a 14 vegades més alta en peu amb PR. Per últim, les simulacions es van repetir utilitzant un model L1-S1 FE de pacient amb propietats del material específics pel pacient (P-SP) i dependents de la condició del teixit. Dempeus, es va predir una activació asimètrica a la banda esquerra i inclinació lateral.La disminució de la capacitat d'inflament dels discs degenerats es va associar a un augment de l'activació muscular necessària per equilibrar les forces de gravetat que tendeixen a flexionar el tronc. La bona correlació dels resultats de l'IDP en el model P-SP amb discos s ans amb dades "in vivo" va contribuir a la validació del mètode presentat. Malgrat les seves limitacions, aquest enfoc va permetre explorar de manera explícita i racional les interaccions entre la funció muscular i la biomecànica dels teixits passius i contribuir a l'enteniment de l'origen de mal d'esquena.Postprint (published version

Biofeedback Based Physical Rehabilitation in Parkinson's Disease Aimed at Self-Enhancement

Parkinson’s disease (PD) is a progressive neuromotor disorder that results in a progressive deterioration of balance and motor abilities with a consequent increase of the risk of falls and a reduction of quality of life. Physical therapy revealed to be fit for the symptomatic treatment of the disease and the adoption of biofeedback signals showed to be effective in prolonging the benefits of the therapy. Thus, this doctoral project has been designed to assess the benefits that wearable technologies for biofeedback generation could have in physical therapy. To further improve the developed biofeedback-based system, the assessment of new methods for the objective evaluation of balance control was included into the study. The dissertation is divided into three different set of studies, respectively aimed at: 1) presenting new wearable systems specifically designed for biofeedback-based rehabilitation; 2) assessing proprioceptive impairments in PD subjects through the adoption of a robotic platform to destabilize the base of support; 3) discussing new methods for the evaluation of balance preceding the execution of voluntary movements. The efficacy of the main proposed solution was assessed in a 6-months RCT study by comparison of subjects with PD trained with the biofeedback system and patients that received usual care. Both clinical and instrumental outcomes supported the higher efficacy of the biofeedback-based approach. The developed instrumented tests showed good sensitivity in discriminating patients and in detecting changes induced by physical therapy. The results reported in this thesis lead to the conclusion that the adoption of biofeedback based physical rehabilitation systems is promising in the treatment of Parkinson’s disease. The availability of a set of fast, easy-to-manage tests for the evaluation of balance and motor control might be useful in the design of home-delivered, user-tailored exercises for both healthy elderly and neurological subjects

Études des mécanismes adaptatifs du maintien de l'équilibre orthostatique. Effets d'une fatigue musculaire, d'une douleur expérimentale et d'une perturbation externe.

Le maintien de l'équilibre orthostatique est une activité motrice primordiale parce qu'elle permet de préserver l'autonomie de chaque individu. Les études présentées dans cette thèse traitent comment diverses contraintes influencent les mécanismes de contrôle impliqués lors du maintien de l'équilibre en station debout. Cette thèse a donc pour objectifs de vérifier : (1) Les effets de la fatigue de certains muscles impliqués dans le contrôle du maintien orthostatique. (2) Les effets d'une douleur expérimentale sur les mécanismes de régulation de l'équilibre orthostatique. (3) Les effets d'une perturbation externe pouvant causer une perte d'équilibre.(4) La validité d'un modèle mathématique démontrant l'importance d'une troisième variable nécessaire pour prédire la stabilité en station debout : le temps de développement du moment de force aux chevilles.En conclusion, cette thèse permet d'éclaircir l'implication des mécanismes adaptatifs du système nerveux dans différents contextes.Premièrement, le système nerveux s'adapteraient à la fatigue des triceps suraux en augmentant la fréquence des ajustements posturaux afin d'éviter des déplacements plus excentriques du centre de masse du corps ou en augmentant les propriétés mécaniques des articulations (i.e. la rigidité). Deuxièmement, une stimulation des nocicepteurs altère principalement les processus sensori-moteurs du système de contrôle postural. La détérioration de la stabilité est fonction de la localisation et de l'intensité de la stimulation douloureuse. La perception de la douleur nécessite des ressources attentionnelles qui ne nuisent pas au contrôle du maintien de l'équilibre en station debout. Troisièmement, l'incertitude reliée à l'avènement probable d'une perturbation provoque une altération des processus de contrôle du maintien de l'équilibre dans les situations sans perturbation et avec perturbation. Quatrièmement, le temps de développement du momentde force aux chevilles contraint la capacité d'une personne à retrouver l'équilibre en station debout suite à une déstabilisation vers l'avant. En ajoutant cette variable à un modèle mathématique, celui-ci permet de prédire 73.3 % des chutes et 73.3 % des stabilisations observées expérimentalement

25th Annual Computational Neuroscience Meeting: CNS-2016

Abstracts of the 25th Annual Computational Neuroscience Meeting: CNS-2016 Seogwipo City, Jeju-do, South Korea. 2–7 July 201

25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong