Repetitive Peripheral Magnetic Stimulation (RPMS) for Rehabilitation of Central Paresis – Clinical Experimental Investigations and Technical Approach

Abstract

Concept of Repetitive Peripheral Magnetic Stimulation (RPMS) is based on the activation of a reorganization process in the CNS (neuromodulation) by induction of a proprioceptive inflow to the CNS, which corresponds physiologically to the lost inflow during active movements. For the induction of this inflow, we use RPMS which depolarizes thick myelinated nerve fibers of the terminal sensorimotor branches. In contrast to fES, the magnetic field penetrates to deeper regions of the muscle, whereas the current caused by the electrical field will take the way of lowest resistance, thus being fairly limited spatially on the surface. Various components of an improvement due to RPMS are clinically and experimentally investigated: 1) Spasticity independent of the level of origin can always be suppressed by RPMS. In a clinical experimental investigation with spastic paresis of finger and hand extensors a dramatic decrease of spasticity together with an increase of voluntary movement could be demonstrated. 2) In a PET study of eight patients it was shown that, due to RPMS, areas of the fronto-parietal circuits which are involved in goal-directed controlled movements, are activated. 3) In disturbed goal-directed motor performances such as reaching and grasping, the regularity of the performed trajectory could be improved. 4) In patients with local tactile extinction (neglect), RPMS reduces the recognition error of different local tactile stimuli. Also the spatial cognition (position sense) can be improved by means of RPMS. We may assume that these various and long-lasting effects on the spinal and cortical levels are based on neuromodulation which is caused by muscle mechanoreceptor afferents. The development of a non-linear adaptive closed-loop control to induce coordinated finger movements by RPMS is the overall target in order to increase the therapeutic outcome. For this purpose our physiological findings from RPMS form the basis to realize the dominant and time-variant components (i.e., recruitment, spasticity, muscle fatigue and rehabilitation progress). These components have to be identified and compensated for by closed-loop control.