Modulation of Stimulation Frequency of Spinal Cord Afferents with Constant Electrode Site and Stimulus Intensity Can Induce a Variety of Movements

摘要

With methodological development for external control of afferents in order to evoke functional movements -afferent functional electrical stimulation (aFES) - we have noticed that frequency of delivered stimuli can have specific influence on motor control. In this report we shall review the finding that selective stimulation of tibial nerve large afferents and selective stimulation of lumbar sacral afferents to the spinal cord can elicit modification of motor output only by changing of the rate of the train of stimuli without changing the stimulus strength or site of stimulation. After a brief description of the applied methods in reported studies of suppression of sustained anti-clonus by train of stimuli of large afferents of tibial nerve at the sensory level, we shall point out that this "anti-clonus" effect depends from a particular frequency range. Other study in which we shall illustrate dependence from frequency rate of motor output it is epidural or transcutaneous stimulation of lumbar posterior roots; and how the frequency of applied stimulation trains can induce two completely different functional outputs of paralyzed lower limbs (standing and locomotor-like movement) due to upper motor neuron lesion. At the end we shall discuss underlying mechanisms of this artificial "coding" in order to induce movement by afferent FES. Finally we shall discuss the significance of these findings for clinical practice of FES in upper motor neuron disorders.