title: Physiological modules for generating discrete and rhythmic movements: action identification by a dynamic recurrent neural network.
abstract: In this study we employed a dynamic recurrent neural network (DRNN) in a novel fashion to reveal characteristics of control modules underlying the generation of muscle activations when drawing figures with the outstretched arm. We asked healthy human subjects to perform four different figure-eight movements in each of two workspaces (frontal plane and sagittal plane). We then trained a DRNN to predict the movement of the wrist from information in the EMG signals from seven different muscles. We trained different instances of the same network on a single movement direction, on all four movement directions in a single movement plane, or on all eight possible movement patterns and looked at the ability of the DRNN to generalize and predict movements for trials that were not included in the training set. Within a single movement plane, a DRNN trained on one movement direction was not able to predict movements of the hand for trials in the other three directions, but a DRNN trained simultaneously on all four movement directions could generalize across movement directions within the same plane. Similarly, the DRNN was able to reproduce the kinematics of the hand for both movement planes, but only if it was trained on examples performed in each one. As we will discuss, these results indicate that there are important dynamical constraints on the mapping of EMG to hand movement that depend on both the time sequence of the movement and on the anatomical constraints of the musculoskeletal system. In a second step, we injected EMG signals constructed from different synergies derived by the PCA in order to identify the mechanical significance of each of these components. From these results, one can surmise that discrete-rhythmic movements may be constructed from three different fundamental modules, one regulating the co-activation of all muscles over the time span of the movement and two others elliciting patterns of reciprocal activation operating in orthogonal directions.
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium ; Laboratorio de Cinesiología y Motricidad, Departamento de Fisiología, Facultad de Medicina y Odontología, Universidad del País Vasco-Euskal Herriko Unibertsitatea (UPV/EHU) Leioa, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Bengoetxea
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Françoise
authors.initials: F
authors.lastname: Leurs
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hoellinger
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Cebolla
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium ; Département de Neurologie, Hôpital Universitaire des Enfants Reine Fabiola, Université Libre de Bruxelles Brussels, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Dan
authors.affiliation: Heath Division, Fondation Tecnalia Research and Innovation San Sebastian, Spain ; IKERBASQUE - Basque Foundation for Science Bilbao, Spain.
authors.forename: Joseph
authors.initials: J
authors.lastname: McIntyre
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium ; Laboratoire d'Électrophysiologie, Université de Mons-Hainaut Mons, Belgium.
authors.forename: Guy
authors.initials: G
authors.lastname: Cheron
keywords: dynamic recurrent neuronal network; figure-eight; muscular synergy; principal component analysis; rhythmic movement; upper limb