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Computer Simulation of the Neural Control of Locomotion in the Cat and the Salamander
KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
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 [en]
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: urn:nbn:se:kth:diva-47362ISBN: 978-91-7501-168-4 (print)OAI: oai:DiVA.org:kth-47362DiVA: diva2:454870
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
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
3. A 3D musculo-mechanical model of the salamander for the study of different gaits and modes of locomotion
Open this publication in new window or tab >>A 3D musculo-mechanical model of the salamander for the study of different gaits and modes of locomotion
2010 (English)In: Frontiers in neurorobotics, ISSN 1662-5218, Vol. 4, 112- p.Article in journal (Refereed) Published
Abstract [en]

Computer simulation has been used to investigate several aspects of locomotion in salamanders. Here we introduce a three-dimensional forward dynamics mechanical model of a salamander, with physically realistic weight and size parameters. Movements of the four limbs and of the trunk and tail are generated by sets of linearly modeled skeletal muscles. In this study, activation of these muscles were driven by prescribed neural output patterns. The model was successfully used to mimic locomotion on level ground and in water. We compare the walking gait where a wave of activity in the axial muscles travels between the girdles, with the trotting gait in simulations using the musculo-mechanical model. In a separate experiment, the model is used to compare different strategies for turning while stepping; either by bending the trunk or by using side-stepping in the front legs. We found that for turning, the use of side-stepping alone or in combination with trunk bending, was more effective than the use of trunk bending alone. We conclude that the musculo-mechanical model described here together with a proper neural controller is useful for neuro-physiological experiments in silico.

Keyword
computer simulation, musculo-mechanical model, pattern generators, salamander locomotion, side-stepping, walking gait
National Category
Bioinformatics (Computational Biology)
Identifiers
urn:nbn:se:kth:diva-39203 (URN)10.3389/fnbot.2010.00112 (DOI)21206530 (PubMedID)2-s2.0-84876144333 (Scopus ID)
Note
QC 20111004Available from: 2011-09-08 Created: 2011-09-08 Last updated: 2011-11-10Bibliographically approved
4. Sensory feedback plays a significant role in generating walking gait and in gait transition in salamanders: a simulation study
Open this publication in new window or tab >>Sensory feedback plays a significant role in generating walking gait and in gait transition in salamanders: a simulation study
Show others...
2011 (English)In: Frontiers in Neurorobotics, ISSN 1662-5218, Vol. 5, 3:1-3:13 p.Article in journal (Refereed) Published
Abstract [en]

Here, we investigate the role of sensory feedback in gait generation and transition by using a three-dimensional, neuro-musculo-mechanical model of a salamander with realistic physical parameters. Activation of limb and axial muscles were driven by neural output patterns obtained from a central pattern generator (CPG) which is composed of simulated spiking neurons with adaptation. The CPG consists of a body-CPG and four limb-CPGs that are interconnected via synapses both ipsilaterally and contralaterally. We use the model both with and without sensory modulation and four different combinations of ipsilateral and contralateral coupling between the limb-CPGs. We found that the proprioceptive sensory inputs are essential in obtaining a coordinated lateral sequence walking gait (walking). The sensory feedback includes the signals coming from the stretch receptor like intraspinal neurons located in the girdle regions and the limb stretch receptors residing in the hip and scapula regions of the salamander. On the other hand, walking trot gait (trotting) is more under central (CPG) influence compared to that of the peripheral or sensory feedback. We found that the gait transition from walking to trotting can be induced by increased activity of the descending drive coming from the mesencephalic locomotor region and is helped by the sensory inputs at the hip and scapula regions detecting the late stance phase. More neurophysiological experiments are required to identify the precise type of mechanoreceptors in the salamander and the neural mechanisms mediating the sensory modulation.

Keyword
computer simulation, gait transition, locomotion, neuronal network, sensory feedback, spiking neurons, walking gait
National Category
Zoology Neurosciences
Identifiers
urn:nbn:se:kth:diva-44040 (URN)10.3389/fnbot.2011.00003 (DOI)2-s2.0-84861945597 (Scopus ID)
Projects
LAMPETRA
Note
QC 20111117Available from: 2011-10-19 Created: 2011-10-19 Last updated: 2011-11-17Bibliographically approved

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