Previous studies have demonstrated that cats during this motor behavior develop extremely high paw velocities and accelerations, the latter often exceeding gravitational acceleration by more than 10 times ( Hoy et al., 1985). This is a spinal reflex, paw-shake response ( Koshland and Smith, 1989 Pearson and Rossignol, 1991), aimed to remove an irritating light object stuck to the paw or foot. We concluded that extreme paw accelerations during paw shaking result from interactions between a spinal CPG, hindlimb segmental inertia, and muscle length/velocity-depended feedback that tunes limb viscoelastic properties.Ĭats produce fast paw oscillations to remove water or adhesive tape on the paw ( Prochazka et al., 1977, 1989 Smith et al., 1980 Abraham and Loeb, 1985 Pearson and Rossignol, 1991 Hodson-Tole et al., 2012 Mehta and Prilutsky, 2014). Manipulating model parameters, including reversal of segmental inertia distal-to-proximal gradient, demonstrated important inertia contribution to developing the segmental velocity/acceleration proximal-to-distal gradient. Simulations reproduced whip-like mechanisms found experimentally: the proximal-to-distal velocity/acceleration gradient, energy transfer by joint forces and energy absorption by distal muscle moments, as well as atypical co-activation of ankle and hip flexors with knee extensors. We then developed a neuromechanical model of hindlimb paw shaking comprised a half-center CPG, activating hip flexors and extensors, and passive viscoelastic distal muscles that produced length/velocity-depended force. Distal muscle moments mostly absorbed energy of the distal segments. This energy transfer was mostly responsible for the segmental velocity/acceleration proximal-to-distal gradient. We first demonstrated in experiments with five intact, adult, female cats that during paw shaking, energy generated by proximal muscle moments was transmitted to distal segments by joint forces. We hypothesized that paw-shaking mechanics and muscle activity might correspond to a whip-like mechanism of energy generation and transfer along the hindlimb. However, mechanisms of developing extreme paw accelerations during paw shaking remain unknown. Previous studies of paw shaking revealed a proximal-to-distal gradient of hindlimb segmental velocities/accelerations, as well as complex inter-joint coordination: passive motion-dependent interaction moments acting on distal segments are opposed by distal muscle moments. 2Dynamical Neuroscience Laboratory, Neuroscience Institute, Georgia State University, Atlanta, GA, United StatesĬat paw shaking is a spinal reflex for removing an irritating stimulus from paw by developing extremely high paw accelerations. ![]() 1Laboratory of Biomechanics and Motor Control, School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, United States.Prilutsky 1*, Jessica Parker 2, Gennady S.
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