Volume 13 Supplement 1
Paw-shake response and locomotion: can one CPG generate two different rhythmic behaviors?
© Klishko et al; licensee BioMed Central Ltd. 2012
Published: 16 July 2012
Rhythmic limb movements like locomotion or paw-shake response are controlled by network of spinal circuits, known as central pattern generators (CPGs), as evidenced from locomotor-like and paw-shake like activity in limb peripheral nerves elicited in decerebrate or spinal animals with blocked neuromuscular transmission . Unlike fictive locomotion and scratch, that are likely controlled by distinct CPGs , fictive paw-shake response has not been systematically investigated and it is not known whether it is controlled by a specialized CPG or by the CPG that also controls locomotion. In-vivo recordings of paw-shake motor patterns elicited by stimulation of paw skin afferents  have revealed high frequency hindlimb oscillations (~10 Hz) with atypical muscle synergies – reciprocal activation of anterior and posterior hindlimb muscles in each half of the paw-shake cycle; both anterior and posterior muscle groups include flexor and extensor muscles. We asked whether a paw-shake response with the atypical muscle synergies can be generated by a typical half-center locomotor CPG reciprocally activating flexor and extensor muscles.
Using software AnimatLab  we developed a 5-segment cat hindlimb model with 12 Hill-type muscle actuators controlled by (1) a half-center CPG activating flexor and extensor muscles (two-joint muscles received both flexion- and extension-related signals [5, 6]) and (2) proprioceptive input originated from the muscle spindle and Golgi tendon organ afferents. The CPG was modeled by two single-compartment spiking neurons in a half-center configuration. Other neurons (Ia-afferents, alpha-motor neurons, Ia-interneurons, and interneurons mediating autogenic and heterogenic reflex pathways) were modeled as non-spiking neurons (firing rate model based on work by ). Model parameters were adjusted such that computer simulations reproduced the recorded paw-shake mechanics and the anterior-posterior muscle activation patterns.
The obtained results demonstrated that a half-center locomotor CPG can produce movement mechanics and muscle activity patterns typical for paw-shake responses if (1) the locomotor CPG is capable to operate at frequencies 3 to10 times higher than during locomotion and (2) synaptic weights in spinal circuits can be modified during paw-shake response. We speculate that the two conditions can be realized by sensory input from paw skin afferents.
Supported by NIH grants: HD-032571, NS-048844, EB012855
- Beer RD, San Diego: Intelligence as adaptive behavior: an experiment in computational neuroethology. 1990, Academic PressGoogle Scholar
- Cofer D, Cymbalyuk G, Reid J, Zhu Y, Heitler WJ, Edwards DH: AnimatLab: a 3D graphics environment for neuromechanical simulations. J. Neurosci Methods. 2010, 187: 280-288. 10.1016/j.jneumeth.2010.01.005.View ArticlePubMedGoogle Scholar
- Frigon A, Gossard JP: Evidence for specialized rhythm-generating mechanisms in the adult mammalian spinal cord. J Neurosci. 2010, 30: 7061-7071. 10.1523/JNEUROSCI.0450-10.2010.View ArticlePubMedGoogle Scholar
- Pearson KG, Rossignol S: Fictive motor patterns in chronic spinal cats. J Neurophysiol. 1991, 66: 1874-1887.PubMedGoogle Scholar
- Perret C, Cabelguen JM: Main characteristics of the hindlimb locomotor cycle in the decorticate cat with special reference to bifunctional muscles. Brain Res. 1980, 187: 333-352. 10.1016/0006-8993(80)90207-3.View ArticlePubMedGoogle Scholar
- Prilutsky BI: Coordination of two- and one-joint muscles: functional consequences and implications for motor control. Motor Control. 2000, 4: 1-44.PubMedGoogle Scholar
- Smith JL, Hoy MG, Koshland GF, Phillips DM, Zernicke RF: Intralimb coordination of the paw-shake response: a novel mixed synergy. J Neurophysiol. 1985, 54: 1271-1281.PubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.