Sensory driven hind-limb mouse locomotion model

In the paper on hind-limb locomotion of a cat in simulation [\textit{reference}], the authors studied the importance two main sensory feedbacks important swing-stance phase switching and which of the particular feedbacks are more important than the other for stable locomotion. In this preliminary work we set-up similar rules to produce locomotion in the mouse model developed in the Neuro-Robotics Platform(NRP). This work will be used to study the role of sensory feedback in locomotion and its integration with feed-forward components such as the Central Pattern Generator’s(CPG’s).In the paper on hind-limb locomotion of a cat in simulation [1], the authors studied the importance two main sensory feedbacks important swing-stance phase switching and which of the particular feedbacks are more important than the other for stable locomotion. In this preliminary work we set-up similar rules to produce locomotion in the mouse model developed in the Neuro-Robotics Platform(NRP). This work will be used to study the role of sensory feedback in locomotion and its integration with feed-forward components such as the Central Pattern Generator’s(CPG’s).


Bio-mechanical model :
We use the Neuro-Robotics platform (NRP) to develop the simulation model and its environment. The rigid body model of the mouse available in NRP was obtained from a high resolution 3D scan of a real mouse. Relationship between the segments are established via joints. For the purpose of this experiment only hind-limbs are actuated. Thus the current model has in total eight actuated joints, four in each hind-limb. Muscles are modeled as hill type muscles with passive and active dynamics. Muscle morphometry and related parameters were obtained from [2]. Each of the actuated joint consisted of at least one pair of antagonist muscle. Some joints also bi-articular muscles. In total the model consists of sixteen muscles. Proprioceptive feedback from muscles and rigid body and tactile information close the loop between the different components of locomotion.

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Reflex controller :
The idea here is to break the motion of hind limb locomotion into four phases, namely (i) swing (ii) touch-down (iii) stance (iv) lift-off. Proprioceptive feedback and joint angles dictate the reflex conditions under which the phase transitions from one to another. Figure shows the four phases and their sequence of transition. For the hind limbs to change from one phase to another we optimize the muscle activation patterns as a function of proprioceptive feedback and joint angle. This ensures a smooth transition between one phase to another when a necessary condition is met.


Discussions :
With the bio-mechanical model of mouse in NRP and reflex control law we are able to reproduce stable hind-limb gait patterns that are purely sensory driven. The next steps to taken in the experiment are :

  1. Convert reflex laws into neuron based reflex loops
  2. Extend the reflex model for quadruped locomotion
  3. Add a CPG layer to interface with the reflex loops

References :

  1. O. Ekeberg and K. Pearson, “Computer simulation of stepping in the hind legs of the cat: an examination of mechanisms regulating the stance-to-swing transition.” Journal of neurophysiology, vol. 94, no. 6, pp. 4256–68, dec 2005.
  2. J. P. Charles, O. Cappellari, A. J. Spence, J. R. Hutchinson, and D. J. Wells, “Musculoskeletal geometry, muscle architecture and functional specialisations of the mouse hindlimb,” PLoS ONE, vol. 11, no. 4, pp. 1–21, 2016.
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