Motor control theories and their applications

Mark L. Latash¹, Mindy F. Levin², John P. Scholz³, Gregor Schöner⁴

¹Department of Kinesiology, The Pennsylvania State University, University Park, PA, USA, ²Department of Physical Therapy, McGill University, Montreal, Canada, ³Department of Physical Therapy, University of Delaware, Newark, DE, USA, ⁴Institute for Neuroinformatics, Ruhr University, Bochum, Germany

Key words: motor control; equilibrium-point hypothesis; synergy; uncontrolled manifold hypothesis; motor disorders.

Summary. We describe several influential hypotheses in the field of motor control including the equilibrium-point (referent configuration) hypothesis, the uncontrolled manifold hypothesis, and the idea of synergies based on the principle of motor abundance. The equilibrium-point hypothesis is based on the idea of control with thresholds for activation of neuronal pools; it provides a framework for analysis of both voluntary and involuntary movements. In particular, control of a single muscle can be adequately described with changes in the threshold of motor unit recruitment during slow muscle stretch (threshold of the tonic stretch reflex). Unlike the ideas of internal models, the equilibrium-point hypothesis does not assume neural computations of mechanical variables. The uncontrolled manifold hypothesis is based on the dynamic system approach to movements; it offers a toolbox to analyze synergic changes within redundant sets of elements related to stabilization of potentially important performance variables. The referent configuration hypothesis and the principle of abundance can be naturally combined into a single coherent scheme of control of multi-element systems. A body of experimental data on healthy persons and patients with movement disorders are reviewed in support of the mentioned hypotheses. In particular, movement disorders associated with spasticity are considered as consequences of an impaired ability to shift threshold of the tonic stretch reflex within the whole normal range. Technical details and applications of the mentioned hypo­theses to studies of motor learning are described. We view the mentioned hypotheses as the most promising ones in the field of motor control, based on a solid physical and neurophysiological foundation.

Correspondence to M. L. Latash, Department of Kinesiology, Rec. Hall-268, Penn State University, University Park, PA 16802, USA. E-mail: mll11@psu.edu

Received 17 May 2010, accepted 7 June 2010