Traveling-wave pattern generator controls movement and organization of sensory feedback in a spinal cord model |
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Authors: | Alexander Kaske Gösta Winberg Joakim Cöster |
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Institution: | (1) Virtual Genetics Laboratory AB and Karolinska Institutet, Microbiology and Tumor Biology Center (MTC), Biocomplexity Group, 17177 Stockholm, Sweden, SE |
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Abstract: | A traveling wave in a two-dimensional spinal cord model constitutes a stable pattern generator for quadruped gaits. In the
context of the somatotopic organization of the spinal cord, this pattern generator is sufficient to generate stable locomotive
limb trajectories. The elastic properties of muscles alone, providing linear negative feedback, are sufficient to stabilize
stance and locomotion in the presence of perturbative forces. We further show that such a pattern generator is capable of
organizing sensory processing in the spinal cord. A single-layer perceptron was trained to associate the sensory feedback
from the limb (coding force, length, and change of length for each muscle) with the two-dimensional activity profile of the
traveling wave. This resulted in a well-defined spatial organization of the connections within the spinal network along a
rostrocaudal axis. The spinal network driven by peripheral afferents alone supported autonomous locomotion in the positive
feedback mode, whereas in the negative feedback mode stance was stabilized in response to perturbations. Systematic variation
of a parameter representing the effect of gamma-motor neurons on muscle spindle activity in our model led to a corresponding
shift of limb position during stance and locomotion, resulting in a systematic displacement alteration of foot positions.
Received: 30 July 2001 / Accepted in revised form: 17 April 2002
Correspondence to: A. Kaske (e-mails: alexander.kaske@mtc.ki.se, alexander.kaske@vglab.com) |
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