title: Physiological modules for generating discrete and rhythmic movements: component analysis of EMG signals.
abstract: A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90°. To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both "discrete-rhythmic movements" such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal.
authors.affiliation: Laboratoire de Neurophysiologie et Biomécanique du Mouvement, Faculté des Sciences de la Motricité, Université Libre de Bruxelles Brussels, Belgium ; Departamento de Fisiología, Laboratorio de Cinesiología y Motricidad, 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 Maria
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: 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
authors.affiliation: Heath Division, Fundacion Tecnalia Research and Innovation San Sebastian, Spain ; IKERBASQUE Science Foundation Bilbao, Spain.
authors.forename: Joseph
authors.initials: J
authors.lastname: McIntyre
keywords: figure-eight; muscular synergy; principal component analysis; rhythmic movement; upper limb; varimax factor analysis