Journal
JOURNAL OF NEUROSCIENCE
Volume 20, Issue 1, Pages 409-426Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.20-01-00409.2000
Keywords
force field; spinal cord; reflex; superposition; primitive; motor control
Categories
Funding
- NICHD NIH HHS [T32 HD007467, 5T32 HD07467] Funding Source: Medline
- NINDS NIH HHS [NS43460, R01 NS040412, R29 NS034640-06, R01 NS040412-01A1, R29 NS034640-02] Funding Source: Medline
- EUNICE KENNEDY SHRIVER NATIONAL INSTITUTE OF CHILD HEALTH &HUMAN DEVELOPMENT [T32HD007467] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE [R29NS034640, R01NS040412] Funding Source: NIH RePORTER
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Spinal circuits form building blocks for movement construction. In the frog, such building blocks have been described as isometric force fields. Microstimulation studies showed that individual force fields can be combined by vector summation. Summation and scaling of a few force-field types can, in theory, produce a large range of dynamic force-field structures associated with limb behaviors. We tested for the first time whether force-field summation underlies the construction of real limb behavior in the frog. We examined the organization of correction responses that circumvent path obstacles during hindlimb wiping trajectories. Correction responses were triggered on-line during wiping by cutaneous feedback signaling obstacle collision. The correction response activated a force field that summed with an ongoing sequence of force fields activated during wiping. Both impact force and time of impact within the wiping motor pattern scaled the evoked correction response amplitude. However, the duration of the correction response was constant and similar to the duration of other muscles activated in different phases of wiping. Thus, our results confirm that both force-field summation and scaling occur during real limb behavior, that force fields represent fixed-timing motor elements, and that these motor elements are combined in chains and in combination contingent on the interaction of feedback and central motor programs.
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