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Computer Simulation of the Neural Control of Locomotion in the Cat
KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
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 [en]
Locomotion, Computer simulation, Central pattern generator, Muscle activation, Linear transfer functions, Sensory feedback, Neural control
National Category
Computer Science
Identifiers
URN: urn:nbn:se:kth:diva-4692ISBN: 978-91-7178-937-2 (print)OAI: oai:DiVA.org:kth-4692DiVA: diva2:13466
Supervisors
Note
QC 20101111Available from: 2008-04-07 Created: 2008-04-07 Last updated: 2010-11-11Bibliographically approved
List of papers
1. Building a computer simulator for the study of stepping of the cat
Open this publication in new window or tab >>Building a computer simulator for the study of stepping of the cat
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.

Series
TRITA-CSC-CB, 2007:01
Keyword
Computer simulation, locomotion, central pattern generator, body dynamics, sensory feedback, muscle model
National Category
Computer Science
Identifiers
urn:nbn:se:kth:diva-26061 (URN)
Note
QC 20101111Available from: 2010-11-11 Created: 2010-11-11 Last updated: 2011-11-10Bibliographically approved
2. System identification of muscle-joint interactions of the cat hind limb during locomotion
Open this publication in new window or tab >>System identification of muscle-joint interactions of the cat hind limb during locomotion
2008 (English)In: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 99, no 2, 125-138 p.Article in journal (Refereed) Published
Abstract [en]

Neurophysiological experiments in walking cats have shown that a number of neural control mechanisms are involved in regulating the movements of the hind legs during locomotion. It is experimentally hard to isolate individual mechanisms without disrupting the natural walking pattern and we therefore introduce a different approach where we use a model to identify what control is necessary to maintain stability in the musculo-skeletal system. We developed a computer simulation model of the cat hind legs in which the movements of each leg are produced by eight limb muscles whose activations follow a centrally generated pattern with no proprioceptive feedback. All linear transfer functions, from each muscle activation to each joint angle, were identified using the response of the joint angle to an impulse in the muscle activation at 65 postures of the leg covering the entire step cycle. We analyzed the sensitivity and stability of each muscle action on the joint angles by studying the gain and pole plots of these transfer functions. We found that the actions of most of the hindlimb muscles display inherent stability during stepping, even without the involvement of any proprioceptive feedback mechanisms, and that those musculo-skeletal systems are acting in a critically damped manner, enabling them to react quickly without unnecessary oscillations. We also found that during the late swing, the activity of the posterior biceps/semitendinosus (PB/ST) muscles causes the joints to be unstable. In addition, vastus lateralis (VL), tibialis anterior (TA) and sartorius (SAT) muscle-joint systems were found to be unstable during the late stance phase, and we conclude that those muscles require neuronal feedback to maintain stable stepping, especially during late swing and late stance phases. Moreover, we could see a clear distinction in the pole distribution (along the step cycle) for the systems related to the ankle joint from that of the other two joints, hip or knee. A similar pattern, i.e., a pattern in which the poles were scattered over the s-plane with no clear clustering according to the phase of the leg position, could be seen in the systems related to soleus (SOL) and TA muscles which would indicate that these muscles depend on neural control mechanisms, which may involve supraspinal structures, over the whole step cycle.

Keyword
locomotion, walking, neural control, spinal cord, computer simulation, system identification, central pattern generation, sensorimotor interactions, unrestrained, locomotion, cutaneous inputs, feline soleus, spinal cats, walking, activation, reflexes, models
National Category
Computer Science
Identifiers
urn:nbn:se:kth:diva-17766 (URN)10.1007/s00422-008-0243-z (DOI)000258527400004 ()2-s2.0-49749094737 (Scopus ID)
Note
QC 20100525 QC 20111109Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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