Synaptic patterning of left-right alternation in a computational model of the rodent hindlimb central pattern generator |
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Authors: | Email author" target="_blank">William?Erik?SherwoodEmail author Ronald?Harris-Warrick John?Guckenheimer |
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Institution: | (1) Center for BioDynamics, Boston University, 111 Cummington Street, Boston, MA 02215, USA;(2) Department of Neurobiology and Behavior, Cornell University, Seeley Mudd Hall, Ithaca, NY 14853, USA;(3) Mathematics Department, Cornell University, 565 Malott Hall, Ithaca, NY 14853, USA |
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Abstract: | Establishing, maintaining, and modifying the phase relationships between extensor and flexor muscle groups is essential for
central pattern generators in the spinal cord to coordinate the hindlimbs well enough to produce the basic walking rhythm.
This paper investigates a simplified computational model for the spinal hindlimb central pattern generator (CPG) that is abstracted
from experimental data from the rodent spinal cord. This model produces locomotor-like activity with appropriate phase relationships
in which right and left muscle groups alternate while extensor and flexor muscle groups alternate. Convergence to this locomotor
pattern is slow, however, and the range of parameter values for which the model produces appropriate output is relatively
narrow. We examine these aspects of the model’s coordination of left-right activity through investigation of successively
more complicated subnetworks, focusing on the role of the synaptic architecture in shaping motoneuron phasing. We find unexpected
sensitivity in the phase response properties of individual neurons in response to stimulation and a need for high levels of
both inhibition and excitation to achieve the walking rhythm. In the absence of cross-cord excitation, equal levels of ipsilateral
and contralateral inhibition result in a strong preference for hopping over walking. Inhibition alone can produce the walking
rhythm, but contralateral inhibition must be much stronger than ipsilateral inhibition. Cross-cord excitatory connections
significantly enhance convergence to the walking rhythm, which is achieved most rapidly with strong crossed excitation and
greater contralateral than ipsilateral inhibition. We discuss the implications of these results for CPG architectures based
on unit burst generators. |
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