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UNCOVERING THE STRUCTURE OF THE MOUSE GAIT CONTROLLER USING MECHANICAL AND NEUROMUSCULAR PERTURBATION OF FREELY RUNNING MICE
Vahedipour, Annie
Vahedipour, Annie
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2018
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Bioengineering
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http://dx.doi.org/10.34944/dspace/583
Abstract
Locomotion is essential to survival in most animals. Studies have shown that animals, including humans, choose a gait that minimizes the risk of injury and maximizes energetic efficiency. Individuals often encounter obstacles and perturbations during normal locomotion, from which they must recover. Despite the importance of understanding the mechanisms that enable recovery from perturbations, ethical and experimental challenges have prevented full exploration of these in legged systems. A powerful paradigm with which to tackle this difficulty would be the application of external and internal manipulation of the nervous system. These perturbations could target how gait is regulated and how the neural systems process sensory information to control locomotion during an unexpected perturbation. Here we present data on the response of female mice to rapid, precisely timed, and spatially confined mechanical perturbations applied by a treadmill system. Our data elucidate that after the mechanical perturbation, the mouse gait response is anisotropic, preferring deviations away from the trot towards bounding, over those towards other gaits, such as walk or pace. We quantified this shift by projecting the observed gait onto the line between trot and bound, in the space of quadrupedal gaits. We call this projection λ. For λ=0, the gait is the ideal trot; for λ=±π, it is the ideal bound. We found that the substrate perturbation caused a significant shift in λ towards bound during the stride in which the perturbation occurred and the following stride (linear mixed effects model: Δλ=0.26±0.07 and Δλ=0.21±0.07, respectively; random effect for animal, p<0.05 for both strides, n = 8 mice). We hypothesize that this is because the bounding gait is better suited to rapid acceleration or deceleration, and an exploratory analysis of jerk showed that it was significantly correlated with λ (p<0.05). To evaluate whether the same structure of gait controller exists when undergoing an entirely different class of manipulation, we applied an internal, neuromuscular perturbation. We directly stimulated the lateral gastrocnemius muscle of mice using implanted electrodes and a custom magnetic headstage. We found that the electrical muscle stimulation caused a significant shift in λ towards bound in trials where the stimulation occurred during the swing phase (linear mixed effects model: Δλ=0.23±0.06 and Δλ=0.28±0.06; for the stride during and after the stimulation, respectively; random effect for animal, p<0.05 for both, n = 7 mice). Understanding how gait is controlled under perturbations can give insight into the neuromechanical basis of locomotion, aid in diagnosing gait pathologies, and aid the design of more agile robots.
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