| 1. |
- Ekeberg, Örjan, 1954-
(författare)
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A combined neuronal and mechanical model of fish swimming
- 1993
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Ingår i: Biological Cybernetics. - 0340-1200 .- 1432-0770. ; 69:5-6, s. 363-374
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Tidskriftsartikel (refereegranskat)abstract
- A simulated neural network has been connected to a simulated mechanical environment. The network is based on a model of the spinal central pattern generator producing rhythmic swimming movements in the lamprey and the model is similar to that used in earlier simulations of fictive swimming. Here, the network has been extended with a model of how motoneuron activity is transformed via the muscles to mechanical forces. Further, these forces are used in a two-dimensional mechanical model including interaction with the surrounding water, giving the movements of the different parts of the body. Finally, these movements are fed back through stretch receptors interacting with the central pattern generator. The combined model provides a platform for various simulation experiments relating the currently known neural properties and connectivity to the behavior of the animal in vivo. By varying a small set of parameters, corresponding to brainstem input to the spinal network, a variety of basic locomotor behaviors, like swimming at different speeds and turning can be produced. This paper describes the combined model and its basic properties.
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| 2. |
- Ekeberg, Örjan, 1954-, et al.
(författare)
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Simulations of neuromuscular control in lamprey swimming
- 1999
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 354:1385, s. 895-902
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Tidskriftsartikel (refereegranskat)abstract
- The neuronal generation of vertebrate locomotion has been extensively studied in the lamprey. Models at different levels of abstraction are being used to describe this system, from abstract nonlinear oscillators to interconnected model neurons comprising multiple compartments and a Hodgkin-Huxley representation of the most relevant ion channels. To study the role of sensory feedback by simulation, it eventually also becomes necessary to incorporate the mechanical movements in the models. By using simplifying models of muscle activation, body mechanics, counteracting water forces, and sensory feedback through stretch receptors and vestibular organs, we have been able to close the feedback loop to enable studies of the interaction between the neuronal and the mechanical systems. The neuromechanical simulations reveal that the currently known network is sufficient for generating a whole repertoire of swimming patterns. Swimming at different speeds and with different wavelengths, together with the performance of lateral turns can all be achieved by simply varying the brainstem input. The neuronal mechanisms behind pitch and roll manoeuvres are less clear. We have put forward a 'crossed-oscillators' hypothesis where partly separate dorsal and ventral circuits are postulated. Neuromechanical simulations of this system show that it is also capable of generating realistic pitch turns and rolls, and that vestibular signals can stabilize the posture during swimming.
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| 3. |
- Ekeberg, Örjan, 1954-, et al.
(författare)
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The Neural Control of Fish Swimming studied through Numerical Simulations
- 1995
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Ingår i: Adaptive Behavior. - : SAGE Publications. - 1059-7123 .- 1741-2633. ; 3:4, s. 363-384
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Tidskriftsartikel (refereegranskat)abstract
- The neuronal generation of vertebrate locomotion has been extensively studied in the lamprey. Computer simulations of this system have been carried out with different aims and with different techniques. in this article, we review some of these simulations, particularly those leading toward models that describe She interaction that occurs between the neuronal system and its mechanical environment during swimming. Here we extend these models, enabling two new experiments to be conducted. The first one addresses the role of sensory feedback by exposing the neuromechanical system to unexpected perturbations. The second one tests the validity of an earlier proposed hypothesis for the neural generation of three-dimensional (3D) steering by coupling this central pattern generator to a mechanical 3D simulation.
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| 4. |
- Hammarlund, Per, et al.
(författare)
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Large neural network simulations on multiple hardware platforms
- 1998
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Ingår i: Journal of Computational Neuroscience. - 0929-5313 .- 1573-6873. ; 5:4, s. 443-459
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Tidskriftsartikel (refereegranskat)abstract
- To efficiently simulate very large networks of interconnected neurons, particular consideration has to be given to the computer architecture being used. This article presents techniques for implementing simulators for large neural networks on a number of different computer architectures. The neuronal simulation task and the computer architectures of interest are first characterized, and the potential bottlenecks are highlighted. Then we describe the experience gained from adapting an existing simulator, sWIM, to two very different architectures-vector computers and multiprocessor workstations. This work lead to the implementation of a new simulation library, SPLIT, designed to allow efficient simulation of large networks on several architectures. Different computer architectures put different demands on the organization of both data structures and computations. Strict separation of such architecture considerations from the neuronal models and other simulation aspects makes it possible to construct both portable and extendible code.
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| 5. |
- Kann, Viggo, 1964-, et al.
(författare)
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Student based program development
- 2018
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Ingår i: ITiCSE 2018 Proceedings of the 23rd Annual ACM Conference on Innovation and Technology in Computer Science Education. - New York, NY, USA : Association for Computing Machinery (ACM). - 9781450357074 ; , s. 379-379
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Konferensbidrag (refereegranskat)abstract
- The aim of this work is to investigate a new method of involving all students in the continued development of an educational program. Using this method, we have obtained a list of well-scrutinized suggestions for improvement that have support among the students, and that we can start to implement. We have also saved a large pool of suggestions that could be used in the future.
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| 6. |
- Natesan, Dinesh
(författare)
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Neuromechanical basis of airflow-dependent antennal positioning in hawkmoths
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fast behaviors, seen in varied life forms, are often considered to be stereotypic and reflexive and the control neural circuits to be hard-wired. However, many such reflexes have been shown to respond in a context-dependent manner. The work presented in this dissertation focuses on uncovering the principles of one such context-dependent behavior - antennal positioning in insects.Insect antennae acquire multimodal sensory cues that are required for a wide range of behaviors. These include odor, temperature, humidity, as well as mechanical vibrations from the surroundings. Each modality encodes a different aspect of the environment and is used appropriately to control behavior. Antennal vibrations, for instance, provide feedback relevant for flight stabilization, and is used to modulate wing movements on short, stroke-to-stroke, timescales. Olfactory cues, on the other hand, indicate presence of food and mates, and are used to alter flight trajectories over longer timescales of multiple wing-strokes. Therefore, for a proper behavioral response, the antennae must optimally acquire sensory cues over multiple timescales. Context-dependent modulation of the antennae perhaps enhances their functionality by tuning their dynamic range.This dissertation focuses on one context, namely airflow, and its effect on antennal positioning. Hawkmoths, and diverse insects, actively position their antennae at the onset of flight by bringing them forward. During flight, they dynamically alter this position based on airflow. Two antennal mechanosensors are involved in this behavior, one being the Böhm’s bristles, which monitors and feeds back the position of the antennae, and the second being the Johnston’s organs, which are stimulated by frontal airflow generated during flight.The first part of the thesis concerns the control algorithms that underlie the sensory integration of antennal mechanosensory input to produce airflow-dependent antennal positioning. Using the Oleander hawkmoth, Daphnis nerii, as a system of study, the behavior is investigated with a combination of experiments and computational techniques. We find that the dynamics of this behavior can be captured by a tunable feedback loop consisting of two components. One, a negative feedback loop that stably maintains antennae at a preferred position, or set-point, using positional feedback from the Böhm’s bristles. Two, a dynamic set-point that is modulated by airflow (and other context specific cues). Furthermore, a minimalistic model neural circuit based on these components simulate airflow-dependent modulation of antennae. Such circuits could enable moths to maintain stable antennal position on short timescales while retaining context-based flexibility over longer durations.The latter half of the thesis focuses on each of the individual components. The neural mechanisms underlying modulation of set-point by the Johnston’s organs are investigated using behavioral and electrophysiological experiments. The positional feedback, sensed and encoded by the Böhm’s bristles, is investigated using biomechanical models. These provide an understanding of how airflow-dependent, or more generally, context-dependent antennal positioning arises as a result of these individual components. As a whole, this dissertation provides a conceptual framework that utilizes experimental and computational techniques to formally describe and understand context-dependent behaviors.
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| 7. |
- Widing, Erik, 1987-, et al.
(författare)
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Tailoring biomechanical model meshes for aero-acoustic simulations
- 2015
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Ingår i: Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization. - : Taylor & Francis Group. - 2168-1171 .- 2168-1163.
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Tidskriftsartikel (refereegranskat)abstract
- To simulate the airflow and acoustic wave propagation associated with voice production, a closed surface mesh representing the vocal tract is needed. Biomechanically, the vocal tract is composed of surfaces from several different anatomical structures. We present a method for assembling a dynamic vocal tract mesh by trimming and stitching surface meshes tracking biomechanical models of relevant structures. Two algorithms, one for trimming and one for stitching, are used to first isolate surface mesh patches that are in contact with the airway and then merge them into a closed surface. The algorithms rely on manually selected boundaries and are able to cover gaps between mesh patches. Test cases are used to illustrate how the algorithms behave in various situations. The algorithms are implemented in the toolkit ArtiSynth where many relevant biomechanical models are already available.
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