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  • 1. Alekseev, A.A
    et al.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Chaotic regime and synchronous response in frequency controlled oscillator1994In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 5, no 1, p. 71-77Article in journal (Refereed)
  • 2. Fagerstedt, P
    et al.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Ullén, F
    Aurell, E
    Lansner, A
    Grillner, S
    computational modeling of turning behavior in lamprey2000Conference paper (Refereed)
  • 3.
    Fransén, Erik
    et al.
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Xie, Yuecong
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Christensen, C.
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Djurfeldt, Mikael
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Ekeberg, Örjan
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Lansner, Anders
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Evaluation of model scalability in parallel neural simulators2005Conference paper (Refereed)
    Abstract [en]

    A long standing belief in neuroscience has been that the brain and specifically the neocortex obtains its computational power by massive parallelism. Albeit conceptually appealing, this notion that effective processing requires large networks has not been possible to test in detailed simulations. In one project, we intend to study the generation of theta activity in the entorhinal-hippocampal system. Several simulation studies indicate that frequency and synchronization of the oscillation generated may depend on density of connectivity and/or geometry of connections. In a second project, we are studying how a model of early visual processing scales towards realistic sizes. To effectively evaluate the model, it must be scaled up to sizes where processing demands from the input given are sufficiently high, and where network size is made sufficiently large to process this information.

    We have in preliminary studies tested two parallel simulators. One is a version of pGENESIS supporting MPI from University of Sunderland, UK. The other is Split, a software produced in our own laboratory. Both have been tested on an Itanium2 cluster. Tests include variable number of processors and scaling number of neurons/compartments or number of synapses. In these simulations, average spike frequency in the network is also varied. The aim is to identify main bottle-necks. For instance, we foresee the need to parallelize the construction/layout of synapses.

  • 4. Grillner, Sten
    et al.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Dario, Paolo
    Stefanini, Cesare
    Menciassi, Arianna
    Lansner, Anders
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Hellgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Modeling a vertebrate motor system: pattern generation, steering and control of body orientation2007In: Progress in Brain Research, ISSN 0079-6123, E-ISSN 1875-7855, Vol. 165, p. 221-234Article, review/survey (Refereed)
    Abstract [en]

    The lamprey is one of the few vertebrates in which the neural control system for goal-directed locomotion including steering and control of body orientation is well described at a cellular level. In this report we review the modeling of the central pattern-generating network, which has been carried out based on detailed experimentation. In the same way the modeling of the control system for steering and control of body orientation is reviewed, including neuromechanical simulations and robotic devices.

  • 5.
    Grillner, Sten
    et al.
    The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet.
    Wallén, Peter
    The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet.
    Saitoh, Kazuya
    The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet.
    Kozlov, Alexander
    The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet.
    Robertson, Brita
    The Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet.
    Neural basis of goal-directed locomotion: An overview2007In: Brain Research Reviews, ISSN 0165-0173, E-ISSN 1872-6321, Vol. 57, no 1, p. 2-12Article in journal (Refereed)
    Abstract [en]

    The different neural control systems involved in goal-directed vertebrate locomotion are reviewed. They include not only the central pattern generator networks in the spinal cord that generate the basic locomotor synergy and the brainstem command systems for locomotion but also the control systems for steering and control of body orientation (posture) and finally the neural structures responsible for determining which motor programs should be turned on in a given instant. The role of the basal ganglia is considered in this context. The review summarizes the available information from a general vertebrate perspective, but specific examples are often derived from the lamprey, which provides the most detailed information when considering cellular and network perspectives.

  • 6.
    Harischandra, Nalin
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Knuesel, Jeremei
    EPFL.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Bicanski, Andrej
    EPFL.
    Cabelguen, Jean-Marie
    Neurocentre Magendie, Bordeaux University, Bordeaux Cedex, France.
    Ijspeert, Auke
    EPFL.
    Ekeberg, Örjan
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sensory feedback plays a significant role in generating walking gait and in gait transition in salamanders: a simulation study2011In: Frontiers in Neurorobotics, ISSN 1662-5218, Vol. 5, p. 3:1-3:13Article in journal (Refereed)
    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.

  • 7.
    Kamali Sarvestani, Iman
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Harischandra, Nalin
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Grillner, Sten
    Karolinska Institutet.
    Ekeberg, Örjan
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    A computational model of visually guided locomotion in lamprey2013In: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 107, no 5, p. 497-512Article in journal (Refereed)
    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.

  • 8.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Full-scale simulations of the lamprey spinal central pattern generator2005Conference paper (Refereed)
  • 9.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Locking response in coupled phase systems1994In: Radiophysics and Quantum Electronics, ISSN 0033-8443, E-ISSN 1573-9120, Vol. 36, no 8, p. 552-554Article in journal (Refereed)
    Abstract [en]

    Some distinctive features of the locking response to a chaotic action are pointed out using the example of coupled phase systems of the delay type: a) the possibility of locking for any values of the parameters of the acting subsystem in the case of precise matching of the response-subsystem parameters; b) relatively low sensitivity to mismatching of the subsystem parameters; and c) mild loss of locking in a nonuniform chain of phase systems.

  • 10.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    The use of synchronized chaos oscillators for transmitting an information signal1994In: Technical physics letters, ISSN 1063-7850, E-ISSN 1090-6533, Vol. 20, no 9, p. 710-712Article in journal (Refereed)
  • 11.
    Kozlov, Alexander K.
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Lansner, Anders
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Grillner, S.
    Hellgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    A hemicord locomotor network of excitatory interneurons: a simulation study2007In: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 96, no 2, p. 229-243Article in journal (Refereed)
    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.

  • 12.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Aurell, E
    Deliagina, T.G
    Grillner, S
    Hellgren-Kotaleski, J
    Orlovsky, G.N
    Zelenin, P.V
    Modeling control of body orientation in the lamprey1999Conference paper (Refereed)
    Abstract [en]

    A phenomenological model of the mechanism of stabilization of the dorsal-side-up orientation in the lamprey is suggested. Mathematical modeling is based on the experimental results on investigation of postural control in lampreys using combined in vivo and robotics approaches. Dynamics of the model agrees qualitatively with the experiment. It is shown by computer simulations that postural correction commands from one or several reticulospinal neurons provide information which may be sufficient for stabilization of body orientation in the lamprey. (C) 2000 Elsevier Science B.V. All rights reserved.

  • 13.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Bazhenov, M.V.
    Huerta, R
    Rabinovich, M.I.
    Multistability in neuronal ensembles with balanced couplings1998In: Bulletin of University of Nizhny Novgorod. RadiofizikaArticle in journal (Refereed)
  • 14.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Fagerstedt, P
    Ullén, F
    Aurell, E
    Turning behavior in lamprey in response to descending unilateral commands: experiments and modeling2000Conference paper (Refereed)
    Abstract [en]

    Steering maneuvers in vertebrates are characterized by asymmetric modulation of the cycle duration and the intensity of the symmetric rhythmic locomotor activity. In the lamprey in vitro model system, turns can be evoked by electrical skin stimuli applied to one side of the head, which give rise to descending unilateral excitatory commands. Turns are observed as increased activity on one side of the spinal cord, followed by a rebound on the other. We investigated the generation of turns in single-segment models of the lamprey locomotor spinal network, and were able to reproduce all main experimental results. Sufficient mechanisms to explain changes in the locomotor rhythm, including rebound, are asymmetric activation of crossing inhibitory neurons, accompanied by a calcium influx in these neurons. (C) 2001 Elsevier Science B.V. All rights reserved.

  • 15.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Hellgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Aurell, Erik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Grillner, S
    Lansner, A
    Modeling of plasticity of the synaptic connections in the lamprey spinal CPG - consequences for network behavior2000In: Neurocomputing, ISSN 0925-2312, E-ISSN 1872-8286, Vol. 32-33, p. 441-446Article in journal (Refereed)
    Abstract [en]

    Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed. This is motivated by the experimentally found effects substance P and 5-hydroxytryptamin (5-HT) have on the inhibitory and excitatory synaptic transmission. The effects can be a change of the amplitude of the postsynaptic potentials as well as induction of an activity-dependent facilitation or depression during repetitive activation. Simulations show that network level effects (i.e. swimming frequency) of substance P and 5-HT can to a substantial part be explained based on their effects on the plasticity of the synaptic transmission.

  • 16.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Hellgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Aurell, Erik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Grillner, S
    Lansner, A
    Modeling of substance P and 5-HT induced synaptic plasticity in the lamprey spinal CPG - consequences for network pattern generation2001In: Journal of Computational Neuroscience, ISSN 0929-5313, E-ISSN 1573-6873, Vol. 11, no 2, p. 183-200Article in journal (Refereed)
    Abstract [en]

    Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed by means of simulations. This is motivated by the effects substance P (a tachykinin) and serotonin (5-hydroxytryptamin; 5-HT) have on synaptic transmission in the locomotor network. Activity-dependent synaptic depression and potentiation have recently been shown experimentally using paired intracellular recordings. Although normally activity-dependent plasticity presumably does not contribute to the patterning of network activity, this changes in the presence of the neuromodulators substance P and 5-HT, which evoke significant plasticity. Substance P can induce a faster and larger depression of inhibitory connections but potentiation of excitatory inputs, whereas 5-HT induces facilitation of both inhibitory and excitatory inputs. Changes in the amplitude of the first postsynaptic potential are also seen. These changes could thus be a potential mechanism underlying the modulatory role these substances have on the rhythmic network activity. The aim of the present study has been to implement the activity dependent synaptic depression and facilitation induced by substance P and 5-HT into two alternative models of the lamprey spinal locomotor network, one relying on reciprocal inhibition for bursting and one in which each hemicord is capable of oscillations. The consequences of the plasticity of inhibitory and excitatory connections are then explored on the network level. In the intact spinal cord, tachykinins and 5-HT, which can be endogenously released, increase and decrease the frequency of the alternating left-right burst pattern, respectively. The frequency decreasing effect of 5-HT has previously been explained based on its conductance decreasing effect on K(Ca) underlying the postspike afterhyperpolarization (AHP). The present simulations show that short-term synaptic plasticity may have strong effects on frequency regulation in the lamprey spinal CPG. In the network model relying on reciprocal inhibition, the observed effects substance P and 5-HT have on network behavior (i.e., a frequency increase and decrease respectively) can to a substantial part be explained by their effects on the total extent and time dynamics of synaptic depression and facilitation. The cellular effects of these substances will in the 5-HT case further contribute to its network effect.

  • 17.
    Kozlov, Alexander
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Hellgren Kotaleski, Jeanette
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Aurell, Erik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Grillner, S.
    Lansner, Anders
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Modeling of plasticity of the synaptic connections in the lamprey spinal CPG - consequences for network behavior2000In: Neurocomputing, ISSN 0925-2312, E-ISSN 1872-8286, Vol. 32, p. 441-446Article in journal (Refereed)
    Abstract [en]

    Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed. This is motivated by the experimentally found effects substance P and 5-hydroxytryptamin (5-HT) have on the inhibitory and excitatory synaptic transmission. The effects can be a change of the amplitude of the postsynaptic potentials as well as induction of an activity-dependent facilitation or depression during repetitive activation. Simulations show that network level effects (i.e. swimming frequency) of substance P and 5-HT can to a substantial part be explained based on their effects on the plasticity of the synaptic transmission.

  • 18.
    Kozlov, Alexander
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Hellgren Kotaleski, Jeanette
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Aurell, Erik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Grillner, S.
    Lansner, Anders
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Modeling of substance P and 5-HT induced synaptic plasticity in the lamprey spinal CPG: Consequences for network pattern generation2001In: Journal of Computational Neuroscience, ISSN 0929-5313, E-ISSN 1573-6873, Vol. 11, no 2, p. 183-200Article in journal (Refereed)
    Abstract [en]

    Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed by means of simulations. This is motivated by the effects substance P (a tachykinin) and serotonin (5-hydroxytryptamin; 5-HT) have on synaptic transmission in the locomotor network. Activity-dependent synaptic depression and potentiation have recently been shown experimentally using paired intracellular recordings. Although normally activity-dependent plasticity presumably does not contribute to the patterning of network activity, this changes in the presence of the neuromodulators substance P and 5-HT, which evoke significant plasticity. Substance P can induce a faster and larger depression of inhibitory connections but potentiation of excitatory inputs, whereas 5-HT induces facilitation of both inhibitory and excitatory inputs. Changes in the amplitude of the first postsynaptic potential are also seen. These changes could thus be a potential mechanism underlying the modulatory role these substances have on the rhythmic network activity. The aim of the present study has been to implement the activity dependent synaptic depression and facilitation induced by substance P and 5-HT into two alternative models of the lamprey spinal locomotor network, one relying on reciprocal inhibition for bursting and one in which each hemicord is capable of oscillations. The consequences of the plasticity of inhibitory and excitatory connections are then explored on the network level. In the intact spinal cord, tachykinins and 5-HT, which can be endogenously released, increase and decrease the frequency of the alternating left-right burst pattern, respectively. The frequency decreasing effect of 5-HT has previously been explained based on its conductance decreasing effect on K underlying the postspike afterhyperpolarization (AHP). The present simulations show that short-term synaptic plasticity may have strong effects on frequency regulation in the lamprey spinal CPG. In the network model relying on reciprocal inhibition, the observed effects substance P and 5-HT have on network behavior (i.e., a frequency increase and decrease respectively) can to a substantial part be explained by their effects on the total extent and time dynamics of synaptic depression and facilitation. The cellular effects of these substances will in the 5-HT case further contribute to its network effect.

  • 19.
    Kozlov, Alexander
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Hellgren Kotaleski, Jeanette
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Wallén, Peter
    Karolinska institutet, Neuroscience.
    Grillner, Sten
    Karolinska institutet, Neuroscience.
    Lansner, Anders
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Detailed reduced models excitatory hemi-cord locomotor network lamprey2003Conference paper (Other academic)
    Abstract [en]

    Rhythmic locomotor-related activity can be induced in the isolated hemi-spinal cord of lamprey during bath application of D-glutamate or NMDA (Cangiano and Grillner, 2003). This bursting activity is not dependent on glycinergic inhibition but relies on mutual glutamatergic excitation among network interneurons. The possibility of such oscillatory activity was suggested by earlier simulations (Hellgren-Kotaleski et al. 1999). Here the underlying mechanisms are further examined using both detailed and reduced mathematical models. The detailed network model comprises a population of compartmental excitatory interneurones with Na+, K+, Ca2+, KCa channels as well as two Ca-pools. The synaptic interactions are mediated by AMPA receptors and voltage-dependent NMDA receptors, as established experimentally. This model reproduces the main experimental observations on both cell and network level, including the slow (NMDA/Mg2+ dependent) and the fast rhythm. Burst frequency can be modulated by changing the AMPA and/or NMDA drive, the latter providing only a narrow dynamic range. Further, the distributed network of the entire hemi-cord has been simulated. A weakly asymmetric rostro-caudal connectivity (stronger descending) could support a uniform intersegmental phase lag along most of the spinal cord, whereas a symmetric connectivity could not. The intersegmental phase lag is effectively controlled (forward and backward direction) by adding excitation or inhibition to the most rostral segments. The detailed model was progressively reduced until only the most important (slow) currents remained. The dynamics of the reduced model followed that of the detailed model. Ca influx and activation of KCa currents was shown to play a key role in the burst generation.

  • 20.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Hellgren-Kotaleski, J
    Aurell, E
    Grillner, S
    Lansner, A
    Modeling of metaplasticity of the synaptic connections in the lamprey spinal CPG---consequences for network behavior1999Conference paper (Refereed)
    Abstract [en]

    Consequences of synaptic plasticity in the lamprey spinal CPG are analyzed by means of simulations. This is motivated by the effects substance P (a tachykinin) and serotonin (5-hydroxytryptamin; 5-HT) have on synaptic transmission in the locomotor network. Activity-dependent synaptic depression and potentiation have recently been shown experimentally using paired intracellular recordings. Although normally activity-dependent plasticity presumably does not contribute to the patterning of network activity, this changes in the presence of the neuromodulators substance P and 5-HT, which evoke significant plasticity. Substance P can induce a faster and larger depression of inhibitory connections but potentiation of excitatory inputs, whereas 5-HT induces facilitation of both inhibitory and excitatory inputs. Changes in the amplitude of the first postsynaptic potential are also seen. These changes could thus be a potential mechanism underlying the modulatory role these substances have on the rhythmic network activity. The aim of the present study has been to implement the activity dependent synaptic depression and facilitation induced by substance P and 5-HT into two alternative models of the lamprey spinal locomotor network, one relying on reciprocal inhibition for bursting and one in which each hemicord is capable of oscillations. The consequences of the plasticity of inhibitory and excitatory connections are then explored on the network level. In the intact spinal cord, tachykinins and 5-HT, which can be endogenously released, increase and decrease the frequency of the alternating left-right burst pattern, respectively. The frequency decreasing effect of 5-HT has previously been explained based on its conductance decreasing effect on K underlying the postspike afterhyperpolarization (AHP). The present simulations show that short-term synaptic plasticity may have strong effects on frequency regulation in the lamprey spinal CPG. In the network model relying on reciprocal inhibition, the observed effects substance P and 5-HT have on network behavior (i.e., a frequency increase and decrease respectively) can to a substantial part be explained by their effects on the total extent and time dynamics of synaptic depression and facilitation. The cellular effects of these substances will in the 5-HT case further contribute to its network effect.

  • 21.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Huerta, R
    Rabinovich, M.I.
    Abarbanel, H.D.I.
    Bazhenov, M.V.
    Neuronal ensembles with balanced interconnection as receptors of information1997In: Doklady physics (Print), ISSN 1028-3358, E-ISSN 1562-6903, Vol. 45, no 12, p. 664-669Article in journal (Refereed)
  • 22.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Huss, Mikael
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Lansner, Anders
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Hellgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Grillner, Sten
    Central and local control principles for vertebrate locomotionManuscript (Other academic)
  • 23.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Huss, Mikael
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Lansner, Anders
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Hellgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Grillner, Sten
    Simple cellular and network control principles govern complex patterns of motor behavior2009In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 106, no 47, p. 20027-20032Article in journal (Refereed)
    Abstract [en]

    The vertebrate central nervous system is organized in modules that independently execute sophisticated tasks. Such modules are flexibly controlled and operate with a considerable degree of autonomy. One example is locomotion generated by spinal central pattern generator networks (CPGs) that shape the detailed motor output. The level of activity is controlled from brainstem locomotor command centers, which in turn, are under the control of the basal ganglia. By using a biophysically detailed, full-scale computational model of the lamprey CPG (10,000 neurons) and its brainstem/forebrain control, we demonstrate general control principles that can adapt the network to different demands. Forward or backward locomotion and steering can be flexibly controlled by local synaptic effects limited to only the very rostral part of the network. Variability in response properties within each neuronal population is an essential feature and assures a constant phase delay along the cord for different locomotor speeds.

  • 24.
    Kozlov, Alexander K.
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Kardamakis, Andreas A.
    Hällgren Kotaleski, Jeanette
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Grillner, Sten
    Gating of steering signals through phasic modulation of reticulospinal neurons during locomotion2014In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 9, p. 3591-3596Article in journal (Refereed)
    Abstract [en]

    The neural control of movements in vertebrates is based on a set of modules, like the central pattern generator networks (CPGs) in the spinal cord coordinating locomotion. Sensory feedback is not required for the CPGs to generate the appropriate motor pattern and neither a detailed control from higher brain centers. Reticulospinal neurons in the brainstem activate the locomotor network, and the same neurons also convey signals from higher brain regions, such as turning/steering commands from the optic tectum (superior colliculus). A tonic increase in the background excitatory drive of the reticulospinal neurons would be sufficient to produce coordinated locomotor activity. However, in both vertebrates and invertebrates, descending systems are in addition phasically modulated because of feedback from the ongoing CPG activity. We use the lamprey as a model for investigating the role of this phasic modulation of the reticulospinal activity, because the brainstem-spinal cord networks are known down to the cellular level in this phylogenetically oldest extant vertebrate. We describe how the phasic modulation of reticulospinal activity from the spinal CPG ensures reliable steering/turning commands without the need for a very precise timing of on-or offset, by using a biophysically detailed large-scale (19,600 model neurons and 646,800 synapses) computational model of the lamprey brainstem-spinal cord network. To verify that the simulated neural network can control body movements, including turning, the spinal activity is fed to a mechanical model of lamprey swimming. The simulations also predict that, in contrast to reticulospinal neurons, tectal steering/turning command neurons should have minimal frequency adaptive properties, which has been confirmed experimentally.

  • 25.
    Kozlov, Alexander K.
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Ullén, F.
    Fagerstedt, P.
    Aurell, Erik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Lansner, Anders
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Grillner, S.
    Mechanisms for lateral turns in lamprey in response to descending unilateral commands: a modeling study2002In: Biological Cybernetics, ISSN 0340-1200, E-ISSN 1432-0770, Vol. 86, no 1, p. 1-14Article in journal (Refereed)
    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.

  • 26.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Lansner, A
    Fagerstedt, P
    Grillner, S
    Collective phenomena in large-scale models of the locomotor spinal network of lamprey2000Conference paper (Refereed)
  • 27.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Lansner, A
    Grillner, S
    Large-scale models of the locomotor spinal network of lamprey2001Conference paper (Refereed)
  • 28.
    Kozlov, Alexander
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Lansner, Anders
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Grillner, S.
    Burst dynamics under mixed NMDA and AMPA drive in the models of the lamprey spinal CPG2003In: Neurocomputing, ISSN 0925-2312, E-ISSN 1872-8286, Vol. 52-54, p. 65-71Article in journal (Refereed)
    Abstract [en]

    The spinal CPG of the lamprey is modeled using a chain of nonlinear oscillators. Each oscillator represents a small neuron population capable of bursting under mixed NMDA and AMPA drive. Parameters of the oscillator are derived from detailed conductance-based neuron models. Analysis and simulations of dynamics of a single oscillator, a chain of locally coupled excitatory oscillators and a chain of two pairs of excitatory and inhibitory oscillators in each segment are done. The roles of asymmetric couplings and additional rostral drive for generation of a traveling wave with one cycle per chain length in a realistic frequency range are studied.

  • 29.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Osipov, G.V
    Shalfeev, V.D
    impulse suppression of chaotic oscillations1996In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 1, p. 113-120Article in journal (Refereed)
    Abstract [en]

    The methods of nonconstant feedback impulse control of chaos are introduced. the approach is based on the similarity of the return of the dissipative continuoustime systems with one dimensional maps. The metods are illustrated for the chua´s circuit Rössler oscillator, and phase-locked loop system.

  • 30.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Osipov, G.V
    Shalfeev, V.D
    impulse suppression of chaotic oscillations in chua's circuit and phase-locked loop1996Conference paper (Refereed)
  • 31.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Osipov, G.V
    Shalfeev, V.D
    Suppressing chaos in continuous systems by impulse control1997Conference paper (Refereed)
    Abstract [en]

    The methods of nonconstant feedback impulse control of chaos are introduced. The approach is based on the similarity of the return maps of dissipative continuous-time systems with one dimensional maps. The methods are illustrated for the Chua's circuit (1992), Rossler oscillator, and phase-locked loop system

  • 32.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Osipov, G.V
    Shalfeev, V.D
    Suppression of chaotic oscillations by external impulse force1996Conference paper (Refereed)
  • 33.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Chaos in controlled generators1995Conference paper (Refereed)
  • 34.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Controlling chaotic oscillations in delayed phase-locked loop1994In: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 2, no 2, p. 36-48Article in journal (Refereed)
  • 35.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Modeling transmission of information using signals with chaotic frequency modulation1996Conference paper (Refereed)
  • 36.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Processing information-bearing chaotic signal in a presence of noise using coupled oscillating systems1995In: Synchronization and Patterns, p. 47-52Article in journal (Refereed)
  • 37.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    selective suppression of deterministic chaotic signals1993In: Technical physics letters, ISSN 1063-7850, E-ISSN 1090-6533, Vol. 19, no 12, p. 769-770Article in journal (Refereed)
  • 38.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Synchronization of adaptive chaotic systems1996Conference paper (Refereed)
  • 39.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Using feedback and directional coupling for signal processing with synchronized chaotic systems1996Conference paper (Refereed)
  • 40.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    Chua, L.O
    Exact synchronization of mismatched chaotic systems1996In: International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, ISSN 0218-1274, Vol. 6, no 3, p. 569-580Article in journal (Refereed)
    Abstract [en]

    In this letter we use adaptive parameter and state feedback control to synchronize two or more slightly mismatched chaotic systems. Chua's circuit with a smooth nonlinearity is used throughout to illustrate our approach. We specify the conditions under which the parameter of a slave system will automatically converge to the parameter of the master system. We also consider potential applications of the control system to problems of secure communications and synchronization of chaos in a chain of slightly different Chua's circuits.

  • 41.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sushchik, M.M
    Molkov, I
    Kuznetsov, A.S
    bistable phase synchronization and chaos in a system of coupled Van der Pol-Duffing oscillators1998Conference paper (Refereed)
    Abstract [en]

    Analysis of numerical solutions for a system of two van der Pol-Duffing oscillators with nonlinear coupling showed that there exist chaotic switchings (occurring at irregular time intervals) between two oscillatory regimes differing by nearly time-constant phase shifts between the coupled subsystems. The analysis includes the investigation of bifurcations of the periodic motions corresponding to synchronization of two subsystems, finding stability regions of synchronization regimes and scenarios of the transitions to chaos.

  • 42.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sushchik, M.M.
    Molkov, Ya. I.
    Kuznetsov, A.S.
    Bistable phase synchronization and chaos in a system of coupled van der Pol-Duffing oscillators1999In: International Journal of Bifurcation and Chaos in Applied Sciences and Engineering, ISSN 0218-1274, Vol. 9, no 12, p. 2271-2278Article in journal (Refereed)
    Abstract [en]

    Analysis of numerical solutions for a system of two van der Pol-Duffing oscillators with nonlinear coupling showed that there exist chaotic switchings (occurring at irregular time intervals) between two oscillatory regimes differing by nearly time-constant phase shifts between the coupled subsystems. The analysis includes the investigation of bifurcations of the periodic motions corresponding to synchronization of two subsystems, finding stability regions of synchronization regimes and scenarios of the transitions to chaos.

  • 43.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sushchik, M.M
    Molkov, Ya. I.
    Kuznetsov, A.S,
    Phase synchronization bistability and chaos in system of two identical Van der Pol-Duffing oscillators1999In: Izvestiya Vysshikh Uchebnykh Zavedenii. Fizika, ISSN 0021-3411, Vol. 7, no 1, p. 68-80Article in journal (Refereed)
  • 44.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sushchik, M.M
    Molkov, Ya.I
    Kuznetsov, A.S
    Phase bistability and chaos in a system of two identical Van der Pol-Duffing oscillators1998Conference paper (Refereed)
  • 45.
    Kozlov, Alexander
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Sushchik, M.M.
    Molkov, Ya.I.
    Kuznetsov, A.S.
    Symmetry breaking, multistability and chaos in a system of two identical van der Pol-Duffing oscillators1998In: Bulletin of university of Nizhny Novgorod. Radiofizika, no 1, p. 89-104Article in journal (Refereed)
  • 46. Lindroos, Robert
    et al.
    Dorst, Matthijs C.
    Du, Kai
    Filipovic, Marko
    Keller, Daniel
    Ketzef, Maya
    Kozlov, Alexander K.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST). KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Kumar, Arvind
    Lindahl, Mikael
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Nair, Anu G.
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Perez-Fernandez, Juan
    Grillner, Sten
    Silberberg, Gilad
    Hällgren Kotaleski, Jeanette
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST). KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Basal Ganglia Neuromodulation Over Multiple Temporal and Structural Scales-Simulations of Direct Pathway MSNs Investigate the Fast Onset of Dopaminergic Effects and Predict the Role of Kv4.22018In: Frontiers in Neural Circuits, ISSN 1662-5110, E-ISSN 1662-5110, Vol. 12, article id 3Article in journal (Refereed)
    Abstract [en]

    The basal ganglia are involved in the motivational and habitual control of motor and cognitive behaviors. Striatum, the largest basal ganglia input stage, integrates cortical and thalamic inputs in functionally segregated cortico-basal ganglia-thalamic loops, and in addition the basal ganglia output nuclei control targets in the brainstem. Striatal function depends on the balance between the direct pathway medium spiny neurons (D1-MSNs) that express D1 dopamine receptors and the indirect pathway MSNs that express D2 dopamine receptors. The striatal microstructure is also divided into striosomes and matrix compartments, based on the differential expression of several proteins. Dopaminergic afferents from the midbrain and local cholinergic interneurons play crucial roles for basal ganglia function, and striatal signaling via the striosomes in turn regulates the midbrain dopaminergic system directly and via the lateral habenula. Consequently, abnormal functions of the basal ganglia neuromodulatory system underlie many neurological and psychiatric disorders. Neuromodulation acts on multiple structural levels, ranging from the subcellular level to behavior, both in health and disease. For example, neuromodulation affects membrane excitability and controls synaptic plasticity and thus learning in the basal ganglia. However, it is not clear on what time scales these different effects are implemented. Phosphorylation of ion channels and the resulting membrane effects are typically studied over minutes while it has been shown that neuromodulation can affect behavior within a few hundred milliseconds. So how do these seemingly contradictory effects fit together? Here we first briefly review neuromodulation of the basal ganglia, with a focus on dopamine. We furthermore use biophysically detailed multi-compartmental models to integrate experimental data regarding dopaminergic effects on individual membrane conductances with the aim to explain the resulting cellular level dopaminergic effects. In particular we predict dopaminergic effects on Kv4.2 in D1-MSNs. Finally, we also explore dynamical aspects of the onset of neuromodulation effects in multi-scale computational models combining biochemical signaling cascades and multi-compartmental neuron models.

  • 47. Molkov, Ya. I.
    et al.
    Sushchik, M.M.
    Kuznetsov, A.S.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Dynamical model of locomotor movements in humans induced by vibration of muscles1998In: Bulletin of University of Nizhny Novgorod. Radiofizika, no 1, p. 63-88Article in journal (Refereed)
  • 48. Molkov, Ya.I
    et al.
    Sushchik, M.M
    Kuznetsov, A.S
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Zakharov, D.G
    Dynamical model for locomotor-like movements of humans1998Conference paper (Refereed)
  • 49. Osipov, G.V
    et al.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D
    controlling chaotic oscillations by impulse feedback1997Conference paper (Refereed)
  • 50. Osipov, G.V.
    et al.
    Kozlov, Alexander
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Shalfeev, V.D.
    Impulse control of chaos in continuous systems1998In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 247, no 1-2, p. 119-128Article in journal (Refereed)
    Abstract [en]

    Several methods of nonconstant feedback impulse control of chaos are proposed. The approach is based on the similarity of the return maps of dissipative continuous-time systems with one-dimensional maps and has a clear geometrical interpretation. The methods are illustrated for Chua's circuit, the Rossler oscillator, and the phase-locked loop system. (C) 1998 Elsevier Science B.V.

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