P247 Basic organization of spinal locomotor network derived from hindlimb design and locomotor demands

Boris I. Prilutsky*1, S. Mohammadali Rahmati#1, Sergey N. Markin2, Natalia A. Shevtsova2, Alain Frigon3, Ilya A. Rybak2, Alexander N. Klishko#1

1School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
2Department of Neurobiology and Anatomy, Drexel University, Philadelphia, PA, USA
3Department of Pharmacology-Physiology, University de Sherbrooke, Sherbrooke, QC, Canada

*Email: boris.priutsky@ap.gatech.edu
#These authors contributed equally to this work


Introduction

One of the core principles of sensorimotor physiology is that the musculoskeletal system and its neural control have coevolved to satisfy behavioural demands. Therefore, it may be possible to derive the organization of the neural control of a motor behaviour (e.g., locomotion) from its mechanical demands and properties of the musculoskeletal system. The goals of this study were to (1) determine activity patterns of cat hindlimb muscles from locomotor demands of walking, (2) determine muscle synergies from the predicted and recorded muscle activity patterns and (3) propose a spinal locomotor network organization based on the derived muscle synergies.

Methods
We defined locomotor demands as patterns of resultant moments of force at hindlimb joints generating walking kinematics. To determine the locomotor demands, we computed the resultant muscle moments (using motion capture and methods of inverse dynamics) and muscle activations producing the moments and minimizing muscle fatigue using optimization. We then derived muscle synergies using the non-negative matrix factorization from the computed and recorded activities. We constructed a rhythm generation and pattern formation network of a spinal central pattern generator (CPG) from the derived muscle synergies and incorporated it into our neuromechanical model of spinal hindlimb locomotion.

Results
Locomotor activity patterns of hindlimb muscles obtained from hindlimb musculoskeletal properties and locomotor demands demonstrated a close agreement with the recorded activity patterns. Muscle synergies and their activation patterns derived from the predicted and measured hindlimb muscle activations were similar and consisted of two flexor and three extensor synergies. We used the revealed muscle synergies to construct a spinal CPG and incorporated it into a neuromechanical model of cat hindlimb locomotion. Computer simulations of locomotion demonstrated realistic locomotor mechanics and activity patterns.

Discussion
We demonstrated that hindlimb musculoskeletal properties and locomotor demands (desired resultant joint moments and minimization of muscle fatigue) can predict hindlimb muscle activation patterns, muscle synergies and a general organization of the CPG. The predicted and recorded muscle activations had the following features: (i) reciprocal activation of antagonists, (ii) concurrent activation of agonists and (iii) dependence of activity of two-joint muscles on functional demands. These muscle activation features are typical for many motor reflexes, automatic and highly skilled motor behaviours and suggest that all these behaviours minimize muscle fatigue and have a common organization of spinal circuitries.




Acknowledgements
This work was supported by US National Institutes of Health grants HD032571 and NS110550.
References
No references