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  • 1. Bem, T.
    et al.
    Cabelguen, J. M.
    Ekeberg, Örjan
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Grillner, S.
    From swimming to walking: a single basic network for two different behaviors2003Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 88, nr 2, s. 79-90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we consider the hypothesis that the spinal locomotor network controlling trunk movements has remained essentially unchanged during the evolutionary transition from aquatic to terrestrial locomotion. The wider repertoire of axial motor patterns expressed by amphibians would then be explained by the influence from separate limb pattern generators, added during this evolution. This study is based on EMG data recorded in vivo from epaxial musculature in the newt Pleurodeles waltl during unrestrained swimming and walking, and on a simplified model of the lamprey spinal pattern generator for swimming. Using computer simulations, we have examined the output generated by the lamprey model network for different input drives. Two distinct inputs were identified which reproduced the main features of the swimming and walking motor patterns in the newt. The swimming pattern is generated when the network receives tonic excitation with local intensity gradients near the neck and girdle regions. To produce the walking pattern, the network must receive (in addition to a tonic excitation at the girdles) a phasic drive which is out of phase in the neck and tail regions in relation to the middle part of the body. To fit the symmetry of the walking pattern, however, the intersegmental connectivity of the network had to be modified by reversing the direction of the crossed inhibitory pathways in the rostral part of the spinal cord. This study suggests that the 'input drive required for the generation of the distinct walking pattern could, at least partly, be attributed to mechanosensory feedback received by the network directly from the intraspinal stretch-receptor system. Indeed, the input drive required resembles the pattern of activity of stretch receptors sensing the lateral bending of the trunk, as expressed during walking in urodeles. Moreover, our results indicate that a nonuniform distribution of these stretch receptors along the trunk can explain the discontinuities exhibited in the swimming pattern of the newt. Thus, original network controlling axial movements not only through a direct coupling at the central level but also via a mechanical coupling between trunk and limbs, which in turn influences the sensory signals sent back to the network. Taken together, our findings support the hypothesis of a phylogenetic conservatism of the spinal locomotor networks generating axial motor patterns from agnathans to amphibians.

  • 2.
    Bicanski, Andrej
    et al.
    School of Engineering, École Polytechnique Fédérale de Lausanne.
    Ryczko, Dimitri
    Département de Physiologie, Université de Montréa.
    Knuesel, Jérémie
    School of Engineering, École Polytechnique Fédérale de Lausanne.
    Harischandra, Nalin
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Charrier, Vanessa
    INSERM U862, Neurocentre Magendie, Université Bordeaux.
    Ekeberg, Örjan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Cabelguen, Jean-Marie
    Neurocentre Magendie, Bordeaux University, Bordeaux Cedex, France.
    Ijspeert, Auke Jan
    School of Engineering, École Polytechnique Fédérale de Lausanne.
    Decoding the mechanisms of gait generation in salamanders by combining neurobiology, modeling and robotics2013Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 107, nr 5, s. 545-564Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Vertebrate animals exhibit impressive locomotor skills. These locomotor skills are due to the complex interactions between the environment, the musculo-skeletal system and the central nervous system, in particular the spinal locomotor circuits. We are interested in decoding these interactions in the salamander, a key animal from an evolutionary point of view. It exhibits both swimming and stepping gaits and is faced with the problem of producing efficient propulsive forces using the same musculo-skeletal system in two environments with significant physical differences in density, viscosity and gravitational load. Yet its nervous system remains comparatively simple. Our approach is based on a combination of neurophysiological experiments, numerical modeling at different levels of abstraction, and robotic validation using an amphibious salamander-like robot. This article reviews the current state of our knowledge on salamander locomotion control, and presents how our approach has allowed us to obtain a first conceptual model of the salamander spinal locomotor networks. The model suggests that the salamander locomotor circuit can be seen as a lamprey-like circuit controlling axial movements of the trunk and tail, extended by specialized oscillatory centers controlling limb movements. The interplay between the two types of circuits determines the mode of locomotion under the influence of sensory feedback and descending drive, with stepping gaits at low drive, and swimming at high drive.

  • 3. Bruederle, Daniel
    et al.
    Petrovici, Mihai A.
    Vogginger, Bernhard
    Ehrlich, Matthias
    Pfeil, Thomas
    Millner, Sebastian
    Gruebl, Andreas
    Wendt, Karsten
    Mueller, Eric
    Schwartz, Marc-Olivier
    de Oliveira, Dan Husmann
    Jeltsch, Sebastian
    Fieres, Johannes
    Schilling, Moritz
    Mueller, Paul
    Breitwieser, Oliver
    Petkov, Venelin
    Muller, Lyle
    Davison, Andrew P.
    Krishnamurthy, Pradeep
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Kremkow, Jens
    Lundqvist, Mikael
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Muller, Eilif
    Partzsch, Johannes
    Scholze, Stefan
    Zuehl, Lukas
    Mayr, Christian
    Destexhe, Alain
    Diesmann, Markus
    Potjans, Tobias C.
    Lansner, Anders
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Schueffny, Rene
    Schemmel, Johannes
    Meier, Karlheinz
    A comprehensive workflow for general-purpose neural modeling with highly configurable neuromorphic hardware systems2011Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 104, nr 4-5, s. 263-296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, we present a methodological framework that meets novel requirements emerging from upcoming types of accelerated and highly configurable neuromorphic hardware systems. We describe in detail a device with 45 million programmable and dynamic synapses that is currently under development, and we sketch the conceptual challenges that arise from taking this platform into operation. More specifically, we aim at the establishment of this neuromorphic system as a flexible and neuroscientifically valuable modeling tool that can be used by non-hardware experts. We consider various functional aspects to be crucial for this purpose, and we introduce a consistent workflow with detailed descriptions of all involved modules that implement the suggested steps: The integration of the hardware interface into the simulator-independent model description language PyNN; a fully automated translation between the PyNN domain and appropriate hardware configurations; an executable specification of the future neuromorphic system that can be seamlessly integrated into this biology-to-hardware mapping process as a test bench for all software layers and possible hardware design modifications; an evaluation scheme that deploys models from a dedicated benchmark library, compares the results generated by virtual or prototype hardware devices with reference software simulations and analyzes the differences. The integration of these components into one hardware-software workflow provides an ecosystem for ongoing preparative studies that support the hardware design process and represents the basis for the maturity of the model-to-hardware mapping software. The functionality and flexibility of the latter is proven with a variety of experimental results.

  • 4.
    Ekeberg, Örjan
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    A combined neuronal and mechanical model of fish swimming1993Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 69, nr 5-6, s. 363-374Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 5.
    Harischandra, Nalin
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Ekeberg, Örjan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    System identification of muscle-joint interactions of the cat hind limb during locomotion2008Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 99, nr 2, s. 125-138Artikel i tidskrift (Refereegranskat)
    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.

  • 6.
    Hellgren Kotaleski, Jeanette
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Grillner, S
    Lansner, A
    Computer simulation of the segmental neural network generating locomotion in lamprey by using populations of network interneurons1992Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 68, s. 1-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Realistic computer simulations of the experimentally established local spinal cord neural network generating swimming in the lamprey have been performed. Populations of network interneurons were used in which cellular properties, like cell size and membrane conductance including voltage dependent ion channels were randomly distributed around experimentally obtained mean values, as were synaptic conductances (kainate/AMPA, NMDA, glycine) and delays. This population model displayed more robust burst activity over a wider frequency range than the more simple subsample model used previously, and the pattern of interneuronal activity was appropriate. The strength of the reciprocal inhibition played a very important role in the regulation of burst frequency, and just by changing the inhibitory bias the entire physiological range could be covered. At the lower frequency range of bursting the segmental excitatory interneurons provide stability as does the activation of voltage dependent NMDA receptors. Spike frequency adaptation by means of summation of afterhyperpolarization (AHP) serves as a major burst terminating factor, and at lower rates the membrane properties conferred by the NMDA receptor activation. The lateral interneurons were not of critical importance for the burst termination. They may, however, be of particular importance for inducing a rapid burst termination during for instance steering and righting reactions. Several cellular factors combine to provide a secure and stable motor pattern in the entire frequency range.

  • 7.
    Hellgren Kotaleski, Jeanette
    et al.
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Grillner, S
    Lansner, Anders
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Computer simulation of the segmental neural network generation locomotion in laprey by using populations of network inteneurons1992Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 68, s. 1-13Artikel i tidskrift (Övrigt vetenskapligt)
  • 8.
    Hellgren Kotaleski, Jeanette
    et al.
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Grillner, Sten
    Lansner, Anders
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Neural mechanisms potentially contributing to the intersegmental phase lag in lamprey I.: Segmental oscillations dependent on reciprocal inhibition1999Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 81, nr 4, s. 317-330Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Factors contributing to the production of a phase lag along chains of oscillatory networks consisting of Hodgkin-Huxley type neurons are analyzed by means of simulations. Simplified network configurations are explored consisting of the basic building blocks of the spinal central pattern generator (CPG) generating swimming in the lamprey. It consists of reciprocally coupled crossed inhibitory C interneurons and ipsilateral excitatory E interneurons that activate C neurons and other E neurons. Oscillatory activity in the model network can, in the simplest case, be produced by a pair of reciprocally coupled C interneurons oscillating through an escape mechanism. Different levels of tonic excitation drive the network over a wide burst frequency range. In this type of network, powerful frequency-regulating factors are the effective inhibition produced by the active side, in combination with the tendency of the inactive side to escape from the inhibition. These two mechanisms can be affected by several factors, e.g. spike frequency adaptation (calcium-dependent K+ channels): N-methyl-D-aspartate membrane properties as well as presence of low-voltage activated calcium channels. A rostrocaudal phase lag can be produced either by extending the contralateral inhibitory projections or the ipsilateral excitatory projections relatively more in the caudal than the rostral direction, since both an increased inhibition and a phasic excitation slow down the receiving network. The phase lag becomes decreased if the length of the intersegmental projections is increased or if the projections are extended symmetrically in both the rostral and the caudal directions. The simulations indicate that the conditions in the ends of an oscillator chain may significantly affect sign, magnitude and constancy of the phase lag. Also, with short and relatively weak intersegmental connections, the network remains robust against perturbations as well as intrinsic frequency differences along the chain. The phase lag (percentage of cycle duration) increases, however, with burst frequency also when the coupling strength is comparatively weak. The results are discussed and compared with previous "phase pulling" models as well as relaxation oscillators.

  • 9.
    Hellgren Kotaleski, Jeanette
    et al.
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Lansner, Anders
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Grillner, Sten
    Neural mechanisms potentially contributing to the intersegmental phase lag in lamprey II.: Hemisegmental oscillations produced by mutually coupled excitatory neurons1999Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 81, nr 4, s. 299-315Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Most previous models of the spinal central pattern generator (CPG) underlying locomotion in the lamprey have relied on reciprocal inhibition between the left and right side for oscillations to be produced. Here, we have explored the consequences of using self-oscillatory hemisegments. Within a single hemisegment, the oscillations are produced by a network of recurrently coupled excitatory neurons (E neurons) that by themselves are not oscillatory but when coupled together through N-methyl-D-aspartate (NMDA) and x-amino-3-hydroxy-5-methyl-4-isoxazolepropionicacid (AMPA)/kainate transmission can produce oscillations. The bursting mechanism relies on intracellular accumulation of calcium that activates Ca2+-dependent KC The intracellular calcium is modeled by two different intracellular calcium pools, one of which represents the calcium entry following the action potential, Ca-AP pool, and the other represents the calcium inflow through the NMDA channels, Ca-NMDA pool. The Ca2+-dependent K+ activated by these two calcium pools are referred to as K-CaAP and K-CaNMDA respectively, and their relative conductances are modulated and increase with the background activation of the network. When changing the background stimulation, the bursting activity in this network can be made to cover a frequency range of 0.5-5.5 Hz with reasonable burst proportions if the adaptation is modulated with the activity. When a chain of such hemisegments are coupled together, a phase lag along the chain can be produced. The local oscillations as well as the phase lag is dependent on the axonal conduction delay as well as the types of excitatory coupling that are assumed, i.e. AMPA/kainate and/or NMDA. When the caudal excitatory projections are extended further than the rostral ones, and assumed to be of approximately equal strength, this kind of network is capable of reproducing several experimental observations such as those occurring during strychnine blockade of the left-right reciprocal inhibition. Addition of reciprocally coupled inhibitory neurons in such a network gives rise to antiphasic activity between the left and right side, but not necessarily to any change of the frequency if the burst proportion of the hemisegmental bursts is well below 50%. Prolongation of the C neuron projection in the rostrocaudal direction restricts the phase lag produced by only the excitatory hemisegmental network by locking together the interburst intervals at different levels of the spinal cord.

  • 10.
    Kamali Sarvestani, Iman
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Kozlov, Alexander
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Harischandra, Nalin
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Grillner, Sten
    Karolinska Institutet.
    Ekeberg, Örjan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    A computational model of visually guided locomotion in lamprey2013Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 107, nr 5, s. 497-512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study addresses mechanisms for the generation and selection of visual behaviors in anamniotes. To demonstrate the function of these mechanisms, we have constructed an experimental platform where a simulated animal swims around in a virtual environment containing visually detectable objects. The simulated animal moves as a result of simulated mechanical forces between the water and its body. The undulations of the body are generated by contraction of simulated muscles attached to realistic body components. Muscles are driven by simulated motoneurons within networks of central pattern generators. Reticulospinal neurons, which drive the spinal pattern generators, are in turn driven directly and indirectly by visuomotor centers in the brainstem. The neural networks representing visuomotor centers receive sensory input from a simplified retina. The model also includes major components of the basal ganglia, as these are hypothesized to be key components in behavior selection. We have hypothesized that sensorimotor transformation in tectum and pretectum transforms the place-coded retinal information into rate-coded turning commands in the reticulospinal neurons via a recruitment network mimicking the layered structure of tectal areas. Via engagement of the basal ganglia, the system proves to be capable of selecting among several possible responses, even if exposed to conflicting stimuli. The anatomically based structure of the control system makes it possible to disconnect different neural components, yielding concrete predictions of how animals with corresponding lesions would behave. The model confirms that the neural networks identified in the lamprey are capable of responding appropriately to simple, multiple, and conflicting stimuli.

  • 11. Kozlov, A. K.
    et al.
    Aurell, Erik
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Orlovsky, G. N.
    Deliagina, T. G.
    Zelenin, P. V.
    Hellgren Kotaleski, Jeanette
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Grillner, S.
    Modeling postural control in the lamprey2001Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 84, nr 5, s. 323-330Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A phenomenological model of the mechanism of stabilization of the body orientation during locomotion (dorsal side up) in the lamprey is presented. The mathematical modeling is based on experimental results obtained during investigations of postural control in lampreys using a combined in vivo and robotics approach. The dynamics of the model agree qualitatively with the experimental data. It is shown by computer simulations that postural correction commands from reticulospinal neurons provide information sufficient to stabilize body orientation in the lamprey. The model is based on differences between the effects exerted by the vestibular apparatus on the left and the right side.

  • 12.
    Kozlov, Alexander K.
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Lansner, Anders
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Grillner, S.
    Hellgren Kotaleski, Jeanette
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    A hemicord locomotor network of excitatory interneurons: a simulation study2007Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 96, nr 2, s. 229-243Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Locomotor burst generation is simulated using a full-scale network model of the unilateral excitatory interneuronal population. Earlier small-scale models predicted that a population of excitatory neurons would be sufficient to produce burst activity, and this has recently been experimentally confirmed. Here we simulate the hemicord activity induced under various experimental conditions, including pharmacological activation by NMDA and AMPA as well as electrical stimulation. The model network comprises a realistic number of cells and synaptic connectivity patterns. Using similar distributions of cellular and synaptic parameters, as have been estimated experimentally, a large variation in dynamic characteristics like firing rates, burst, and cycle durations were seen in single cells. On the network level an overall rhythm was generated because the synaptic interactions cause partial synchronization within the population. This network rhythm not only emerged despite the distributed cellular parameters but relied on this variability, in particular, in reproducing variations of the activity during the cycle and showing recruitment in interneuronal populations. A slow rhythm (0.4-2 Hz) can be induced by tonic activation of NMDA-sensitive channels, which are voltage dependent and generate depolarizing plateaus. The rhythm emerges through a synchronization of bursts of the individual neurons. A fast rhythm (4-12 Hz), induced by AMPA, relies on spike synchronization within the population, and each burst is composed of single spikes produced by different neurons. The dynamic range of the fast rhythm is limited by the ability of the network to synchronize oscillations and depends on the strength of synaptic connections and the duration of the slow after hyperpolarization. The model network also produces prolonged bouts of rhythmic activity in response to brief electrical activations, as seen experimentally. The mutual excitation can sustain long-lasting activity for a realistic set of synaptic parameters. The bout duration depends on the strength of excitatory synaptic connections, the level of persistent depolarization, and the influx of Ca2+ ions and activation of Ca2+-dependent K+ current.

  • 13.
    Kozlov, Alexander K.
    et al.
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Ullén, F.
    Fagerstedt, P.
    Aurell, Erik
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Lansner, Anders
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Grillner, S.
    Mechanisms for lateral turns in lamprey in response to descending unilateral commands: a modeling study2002Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 86, nr 1, s. 1-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Straight locomotion in the lamprey is, at the segmental level, characterized by alternating bursts of motor activity with equal duration and spike frequency on the left and the right sides of the body. Lateral turns are characterized by three main changes in this pattern: (1) in the turn cycle, the spike frequency, burst duration, and burst proportion (burst duration/cycle duration) increase on the turning side; (2) the cycle duration increases in both the turn cycle and the succeeding cycle; and (3) in the cycle succeeding the turn cycle, the burst duration increases on the non-turning side (rebound). We investigated mechanisms for the generation of turns in single-segment models of the lamprey locomotor spinal network. Activation of crossing inhibitory neurons proved a sufficient mechanism to explain all three changes in the locomotor rhythm during a fictive turn. Increased activation of these cells inhibits the activity of the opposite side during the prolonged burst of the turn cycle, and slows down the locomotor rhythm. Secondly, this activation of the crossing inhibitory neurons is accompanied by an increased calcium influx into the cells. This gives a suppressed activity on the turning side and a contralateral rebound after the turn, through activation of calcium-dependent potassium channels.

  • 14.
    Lindeberg, Tony
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    A computational theory of visual receptive fields2013Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 107, nr 6, s. 589-635Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A receptive field constitutes a region in the visual field where a visual cell or a visual operator responds to visual stimuli. This paper presents a theory for what types of receptive field profiles can be regarded as natural for an idealized vision system, given a set of structural requirements on the first stages of visual processing that reflect symmetry properties of the surrounding world.

    These symmetry properties include (i) covariance properties under scale changes, affine image deformations, and Galilean transformations of space–time as occur for real-world image data as well as specific requirements of (ii) temporal causality implying that the future cannot be accessed and (iii) a time-recursive updating mechanism of a limited temporal buffer of the past as is necessary for a genuine real-time system. Fundamental structural requirements are also imposed to ensure (iv) mutual consistency and a proper handling of internal representations at different spatial and temporal scales.

    It is shown how a set of families of idealized receptive field profiles can be derived by necessity regarding spatial, spatio-chromatic, and spatio-temporal receptive fields in terms of Gaussian kernels, Gaussian derivatives, or closely related operators. Such image filters have been successfully used as a basis for expressing a large number of visual operations in computer vision, regarding feature detection, feature classification, motion estimation, object recognition, spatio-temporal recognition, and shape estimation. Hence, the associated so-called scale-space theory constitutes a both theoretically well-founded and general framework for expressing visual operations.

    There are very close similarities between receptive field profiles predicted from this scale-space theory and receptive field profiles found by cell recordings in biological vision. Among the family of receptive field profiles derived by necessity from the assumptions, idealized models with very good qualitative agreement are obtained for (i) spatial on-center/off-surround and off-center/on-surround receptive fields in the fovea and the LGN, (ii) simple cells with spatial directional preference in V1, (iii) spatio-chromatic double-opponent neurons in V1, (iv) space–time separable spatio-temporal receptive fields in the LGN and V1, and (v) non-separable space–time tilted receptive fields in V1, all within the same unified theory. In addition, the paper presents a more general framework for relating and interpreting these receptive fields conceptually and possibly predicting new receptive field profiles as well as for pre-wiring covariance under scaling, affine, and Galilean transformations into the representations of visual stimuli.

    This paper describes the basic structure of the necessity results concerning receptive field profiles regarding the mathematical foundation of the theory and outlines how the proposed theory could be used in further studies and modelling of biological vision. It is also shown how receptive field responses can be interpreted physically, as the superposition of relative variations of surface structure and illumination variations, given a logarithmic brightness scale, and how receptive field measurements will be invariant under multiplicative illumination variations and exposure control mechanisms.

  • 15.
    Manfredi, L
    et al.
    Institute for Medical Science and Technology (IMSaT), University of Dundee, Wilson House, 1 Wurzburg Loan, Dundee Medipark, Dundee DD2 1FD, UK.
    Assaf, T.
    Bristol Robotics Laboratory, Frenchay Campus, Bristol BS16 1QY, UK.
    Mintchev, S.
    The BioRobotics Institute, Scuola Superiore Sant’Anna (SSSA), Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy.
    Marrazza, S.
    The BioRobotics Institute, Scuola Superiore Sant’Anna (SSSA), Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy.
    Capantini, L.
    Department of Neuroscience, Nobel Institute for Neurophysiology, Karolinska Institutet.
    Orofino, S.
    The BioRobotics Institute, Scuola Superiore Sant’Anna (SSSA), Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy.
    Ascari, L.
    HENESIS srl, Viale dei Mille 108, 43125 Parma, Italy.
    Grillner, Sten
    Department of Neuroscience, Nobel Institute for Neurophysiology, Karolinska Institutet.
    Wallén, Peter
    Department of Neuroscience, Nobel Institute for Neurophysiology, Karolinska Institutet.
    Ekeberg, Örjan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsbiologi, CB.
    Stefanini, C.
    The BioRobotics Institute, Scuola Superiore Sant’Anna (SSSA), Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy.
    Dario, Paulo
    The BioRobotics Institute, Scuola Superiore Sant’Anna (SSSA), Viale Rinaldo Piaggio 34, 56025 Pontedera (Pisa), Italy.
    A bioinspired autonomous swimming robot as a tool for studying goal-directed locomotion2013Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 107, nr 5, s. 513-527Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The bioinspired approach has been key in combining the disciplines of robotics with neuroscience in an effective and promising fashion. Indeed, certain aspects in the field of neuroscience, such as goal-directed locomotion and behaviour selection, can be validated through robotic artefacts. In particular, swimming is a functionally important behaviour where neuromuscular structures, neural control architecture and operation can be replicated artificially following models from biology and neuroscience. In this article, we present a biomimetic system inspired by the lamprey, an early vertebrate that locomotes using anguilliform swimming. The artefact possesses extra- and proprioceptive sensory receptors, muscle-like actuation, distributed embedded control and a vision system. Experiments on optimised swimming and on goal-directed locomotion are reported, as well as the assessment of the performance of the system,which shows high energy efficiency and adaptive behaviour. While the focus is on providing a robotic platform for testing biological models, the reported system can also be of major relevance for the development of engineering system applications.

  • 16. Ullström, M
    et al.
    Hellgren Kotaleski, Jeanette
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Tegnér, Jon
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Aurell, Erik
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Grillner, Sten
    Lansner, Anders
    KTH, Tidigare Institutioner, Numerisk analys och datalogi, NADA.
    Activity-dependent modulation of adaptation produces a constant burst proportion in a model of the lamprey spinal locomotor generator.1998Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 79, nr 1, s. 1-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The neuronal network underlying lamprey swimming has stimulated extensive modelling on different levels of abstraction. The lamprey swims with a burst frequency ranging from 0.3 to 8-10 Hz with a rostrocaudal lag between bursts in each segment along the spinal cord. The swimming motor pattern is characterized by a burst proportion that is independent of burst frequency and lasts around 30%-40% of the cycle duration. This also applies in preparations in which the reciprocal inhibition in the spinal cord between the left and right side is blocked. A network of coupled excitatory neurons producing hemisegmental oscillations may form the basis of the lamprey central pattern generator (CPG). Here we explored how such networks, in principle, could produce a large frequency range with a constant burst proportion. The computer simulations of the lamprey CPG use simplified, graded output units that could represent populations of neurons and that exhibit adaptation. We investigated the effect of an active modulation of the degree of adaptation of the CPG units to accomplish a constant burst proportion over the whole frequency range when, in addition, each hemisegment is assumed to be self-oscillatory. The degree of adaptation is increased with the degree of stimulation of the network. This will make the bursts terminate earlier at higher burst rates, allowing for a constant burst proportion. Without modulated adaptation the network operates in a limited range of swimming frequencies due to a progressive increase of burst duration with increasing background stimulation. By introducing a modulation of the adaptation, a broad burst frequency range can be produced. The reciprocal inhibition is thus not the primary burst terminating factor, as in many CPG models, and it is mainly responsible for producing alternation between the left and right sides. The results are compared with the Morris-Lecar oscillator model with parameters set to produce a type A and type B oscillator, in which the burst durations stay constant or increase, respectively, when the background stimulation is increased. Here as well, burst duration can be controlled by modulation of the slow variable in a similar way as above. When oscillatory hemisegmental networks are coupled together in a chain a phase lag is produced. The production of a phase lag in chains of such oscillators is compared with chains of Morris-Lecar relaxation oscillators. Models relating to the intact versus isolated spinal cord preparation are discussed, as well as the role of descending inhibition.

  • 17.
    Wadden, Tom
    et al.
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Hellgren Kotaleski, Jeanette
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Lansner, Anders
    KTH, Tidigare Institutioner                               , Numerisk analys och datalogi, NADA.
    Grillner, Sten
    Intersegmental coordination in the lamprey: Simulations using a network model without segmental boundaries1997Ingår i: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 76, nr 1, s. 1-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Swimming in vertebrates such as eel and lamprey involves the coordination of alternating left and right activity in each segment. Forward swimming is achieved by a lag between the onset of activity in consecutive segments rostrocaudally along the spinal cord. The intersegmental phase lag is approximately 1% of the cycle duration per segment and is independent of the swimming frequency. Since the lamprey has approximately 100 spinal segments, at any given time one wave of activity is propagated along the body. Most previous simulations of intersegmental coordination in the lamprey have treated the cord as a chain of coupled oscillators or well-defined segments. Here a network model without segmental boundaries is described which can produce coordinated activity with a phase lag. This 'continuous' pattern-generating network is composed of a column of 420 excitatory interneurons (E1 to E420) and 300 inhibitory interneurons (C1 to C300) on each half of the simulated spinal cord. The interneurons are distributed evenly along the simulated spinal cord, and their connectivity is chosen to reflect the behavior of the intact animal and what is known about the length and strength of the synaptic connections. For example, E100 connects to all interneurons between E51 and E149, but at varying synaptic strengths, while E101 connects to all interneurons between E52 and E150. This unsegmented E-C network generates a motor pattern that is sampled by output elements similar to motoneurons (M cells), which are arranged along the cell column so that they receive input from seven E and five C interneurons. The M cells thus represent the summed excitatory and inhibitory input at different points along the simulated spinal cord and can be regarded as representing the ventral root output to the myotomes along the spinal cord. E and C interneurons have five simulated compartments and Hodgkin-Huxley based dynamics. The simulated network produces rhythmic output over a wide range of frequencies (1-11 Hz) with a phase lag constant over most of the length, with the exception of the 'cut' ends due to reduced synaptic input. As the inhibitory C interneurons in the simulation have more extensive caudal than rostral projections, the output of the simulation has positive phase lags, as occurs in forward swimming. However, unlike the biological network, phase lags in the simulation increase significantly with burst frequency, from 0.5% to 2.3% over the range of frequencies of the simulation. Local rostral or caudal increases in excitatory drive in the simulated network are sufficient to produce motor patterns with increased or decreased phase lags, respectively.

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