Frequency-dependent selection of alternative spinal pathways with common periodic sensory input.
Electrical stimulation of the lumbar cord at distinct frequency ranges has been shown to evoke either rhythmical, step-like movements (25-50 Hz) or a sustained extension (5-15 Hz) of the paralysed lower limbs in complete spinal cord injured subjects. Frequency-dependent activation of previously "silent" spinal pathways was suggested to contribute to the differential responsiveness to distinct neuronal "codes" and the modifications in the electromyographic recordings during the actual implementation of the evoked motor tasks. In the present study we examine this suggestion by means of a simplified biology-based neuronal network. Involving two basic mechanisms, temporal summation of synaptic input and presynaptic inhibition, the model exhibits several patterns of mono- and/or oligo-synaptic motor output in response to different interstimulus intervals. It thus reproduces fundamental input-output features of the lumbar cord isolated from the brain. The results confirm frequency-dependent spinal pathway selection as a simple mechanism which enables the cord to respond to distinct neuronal codes with different motor behaviours and to control the actual performance of the latter.
Jilge
Bernhard
B
TU-BioMed Association for Biomedical Engineering, Vienna University of Technology, Wiedner Hauptstrasse 8-10, 1040 Vienna, Austria.
Minassian
Karen
K
Rattay
Frank
F
Dimitrijevic
Milan R
MR
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D005684:Gait / Q000502:physiology; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008161:Lumbosacral Region; D008959:Models, Neurological; D009068:Movement / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D016571:Neural Networks, Computer; D009434:Neural Pathways / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D012018:Reflex / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology