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Abnormal sensorimotor control, but intact forcefield adaptation, in multiple sclerosis subjects with no clinical disability

¹ Department of Informatics, Systems and Telematics and Research Centre for Neuroscience and Neuroengineering,University of Genoa, via Opera Pia 13, Genoa 16145, Italy and Foundation Don Gnocchi, via Cisa Vecchia, 19038 Sarzana SP, Italy
² Department of Informatics, Systems and Telematics and Research Centre for Neuroscience and Neuroengineering, University of Genoa, via Opera Pia 13, Genoa 16145, Italy
³ Department of Neurology, Hospital PA Micone, Genoa, Italy

^* To whom correspondence should be addressed.

	Abstract

In MS subjects with no clinical disability, we assessed sensorimotor organization and their ability to adapt to an unfamiliar dynamical environment. Eleven MS subjects performed reaching movements while a robot generated a speed-dependent force field. Control and adaptation performance were compared with that of an equal number of control subjects. During a familiarization phase, when the robot generated no forces, the movements of MS subjects were more curved, displayed greater and more variable directional errors and a longer deceleration phase. During the force field phase, both MS and control subjects gradually learned to predict the robot-generated forces. The rates of adaptationwere similar, but MS subjects showed a greater variability in responding to the force field. These results suggest that MS subjects have a preserved capability of learning to predict the effects of the forces, but make greater errors when actually using such predictions to generate movements. Inaccurate motor commands are then compensated later in the movement through an extra amount of sensory-based corrections. This indicates that early in the disease MS subjects have intact adaptive capabilities, but impaired movement execution.

Key Words: motor adaptation; motor control; multiple sclerosis; robot therapy

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