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Building a computer simulator for the study of stepping of the cat
KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
2007 (English)Report (Other academic)
Abstract [en]

We have developed a 3-dimensional computer simulator for investigation on the neuro-musculo-skeletal system and its interactions during normal walking of the cat. Main components of the cat model are the simulation of skeletal dynamics and the control system that includes a mathematical muscle model and a central pattern generator (CPG) network. The simulator is programmed in Python scripting language with other supported open source libraries such as Open Dynamics Engine (ODE) for body dynamics and Opengl for 3-D graphical representation. Modular structure and the object oriented programming technique allows easy access to the model parameters and the modules can be easily modified without altering the entire program. To test the model’s functionality, a simple experiment, during which the cat was set to walk on a flat surface with only the hind legs’ muscles were controlled by two separate CPGs with no sensory feed back, was carried out. It was possible to obtain a realistic stepping in the hind legs even without sensory feedback to the two controllers for each leg. We conclude that the mechanical linkages between the legs also play a major role in producing alternating gait.

Place, publisher, year, edition, pages
2007.
Series
TRITA-CSC-CB, 2007:01
Keyword [en]
Computer simulation, locomotion, central pattern generator, body dynamics, sensory feedback, muscle model
National Category
Computer Science
Identifiers
URN: urn:nbn:se:kth:diva-26061OAI: oai:DiVA.org:kth-26061DiVA: diva2:369620
Note
QC 20101111Available from: 2010-11-11 Created: 2010-11-11 Last updated: 2011-11-10Bibliographically approved
In thesis
1. Computer Simulation of the Neural Control of Locomotion in the Cat
Open this publication in new window or tab >>Computer Simulation of the Neural Control of Locomotion in the Cat
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Locomotion is one of the most important behaviours and requires interaction between sensors at various levels of the nervous system and the limb muscles of an animal. The basic neural rhythm for locomotion in mammals has been shown to arise from local neural networks residing in the spinal cord and these networks are known as central pattern generators (CPGs). However, during the locomotion, these centres are constantly interacting with the sensory feedback signals coming from muscles, joints and peripheral skin receptors in order to adapt the stepping to varying environmental conditions. Conceptual models of mammalian locomotion have been constructed using

mathematical models of locomotor subsystems based on the abundance of neurophysiological evidence obtained primarily in the cat. Several aspects of locomotor control using the cat as an animal model have been investigated employing computer simulations and here we use the same approach to address number of questions or/and hypotheses related to rhythmic locomotion in quadrupeds. Some of the involve questions are, role of mechanical linkage during deafferented walking, finding inherent stabilities/instabilities of muscle-joint interactions during normal walking, estimating phase dependent controlability of muscle action over joints.

This thesis presents the basics of a biologically realistic model of mammalian locomotion and summarises methodological approaches in modelling quadruped locomotor subsystems such as CPGs, limb muscles and sensory pathways. In the first appended article, we extensively discuss the construction details of the three-dimensional computer simulator for the study of the hind leg neuro-musculo-skeletal-control system and its interactions during normal walking of the cat. The simulator with the walking model is programmed in Python scripting language with other supported open source libraries such as Open Dynamics Engine (ODE) for simulating body dynamics and OpenGL for three dimensional graphical representation. We have examined the

functionality of the simulator and the walking model by simulating deafferented walking. It was possible to obtain a realistic stepping in the hind legs even without sensory feedback to the two controllers (CPGs) for each leg. We conclude that the mechanical linkages between the legs also play a major role in producing alternating gait.

The use of simulations of walking in the cat for gaining insights into more complex interactions between the environment and the neuro-muscular-skeletal system is important especially for questions where a direct neurophysiological experiment can not be performed on a real walking animal. For instance, it is experimentally hard to isolate individual mechanisms without disrupting the natural walking pattern. In the second article, we introduce a different approach where we use the walking model to identify what control is necessary to maintain stability in the musculo-skeletal system. We show that the actions of most of the hindlimb muscles over the joints have an inherent stability during stepping, even without the involvement of proprioceptive feedback mechanisms. In addition, we observe that muscles generating movements in the ankle joint of the hind leg must be controlled by neural mechanisms, which may involve supraspinal structures, over the whole step cycle.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xiv, 60 p.
Series
Trita-CSC-A, ISSN 1653-5723 ; 2008:4
Keyword
Locomotion, Computer simulation, Central pattern generator, Muscle activation, Linear transfer functions, Sensory feedback, Neural control
National Category
Computer Science
Identifiers
urn:nbn:se:kth:diva-4692 (URN)978-91-7178-937-2 (ISBN)
Supervisors
Note
QC 20101111Available from: 2008-04-07 Created: 2008-04-07 Last updated: 2010-11-11Bibliographically approved
2. Computer Simulation of the Neural Control of Locomotion in the Cat and the Salamander
Open this publication in new window or tab >>Computer Simulation of the Neural Control of Locomotion in the Cat and the Salamander
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Locomotion is an integral part of a whole range of animal behaviours. The basic rhythm for locomotion in vertebrates has been shown to arise from local networks residing in the spinal cord and these networks are known as central pattern generators (CPG). However, during the locomotion, these centres are constantly interacting with the sensory feedback signals coming from muscles, joints and peripheral skin receptors in order to adapt the stepping or swimming to varying environmental conditions. Conceptual models of vertebrate locomotion have been constructed using mathematical models of locomotor subsystems based on the neurophysiological evidence obtained primarily in the cat and the salamander, an amphibian with a sprawling posture. Such models provide opportunity for studying the key elements in the transition from aquatic to terrestrial locomotion. Several aspects of locomotor control using the cat or the salamander as an animal model have been investigated employing computer simulations and here we use the same approach to address a number of questions or/and hypotheses related to rhythmic locomotion in quadrupeds. Some of the involved questions are, the role of mechanical linkage during deafferented walking, finding inherent stabilities/instabilities of muscle-joint interactions during normal walking and estimating phase dependent controlability of muscle action over joints. Also we investigate limb and body coordination for different gaits, use of side-stepping in front limbs for turning and the role of sensory feedback in gait generation and transitions in salamanders.

     This thesis presents the basics of the biologically realistic models of cat and salamander locomotion and summarizes computational methods in modeling quadruped locomotor subsystems such as CPG, limb muscles and sensory pathways. In the case of cat hind limb, we conclude that the mechanical linkages between the legs play a major role in producing the alternating gait. In another experiment we use the model to identify open-loop linear transfer functions between muscle activations and joint angles while ongoing locomotion. We hypothesize that the musculo-skeletal system for locomotion in animals, at least in cats, operates under critically damped condition.

     The 3D model of the salamander is successfully used to mimic locomotion on level ground and in water. We compare the walking gait with the trotting gait in simulations. We also found that for turning, the use of side-stepping alone or in combination with trunk bending is more effective than the use of trunk bending alone. The same model together with a more realistic CPG composed of spiking neurons was used to investigate the role of sensory feedback in gait generation and transition. We found that the proprioceptive sensory inputs are essential in obtaining the walking gait, whereas the trotting gait is more under central (CPG) influence compared to that of the peripheral or sensory feedback.

     This thesis work sheds light on understanding the neural control mechanisms behind vertebrate locomotion. Additionally, both neuro-mechanical models can be used for further investigations in finding new control algorithms which give robust, adaptive, efficient and realistic stepping in each leg, which would be advantageous since it can be implemented on a controller of a quadruped-robotic device.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xiv, 99 p.
Series
Trita-CSC-A, ISSN 1653-5723 ; 2011:20
Keyword
Locomotion, Computer simulation, Central pattern generator, System identification, Gait transition, Sensory feedback, Spiking neural networks
National Category
Computer Science Bioinformatics (Computational Biology) Computer Systems Control Engineering
Identifiers
urn:nbn:se:kth:diva-47362 (URN)978-91-7501-168-4 (ISBN)
Public defence
2011-12-14, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme
Note
This work is Funded by Swedish International Development cooperation Agency (SIDA). QC 20111110Available from: 2011-11-10 Created: 2011-11-08 Last updated: 2011-11-10Bibliographically approved

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