| 1. |
- Djurfeldt, Mikael, et al.
(författare)
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Cortex-basal ganglia interaction and attractor states
- 2001
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 38-40, s. 573-579
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Tidskriftsartikel (refereegranskat)abstract
- We propose a set of hypotheses about how the basal ganglia contribute to information processing in cortical networks and how the cortex and basal ganglia interact during learning and behavior. We introduce a computational model on the level of system of networks. We suggest that the basal ganglia control cortical activity by pushing a local cortical network into a new attractor state, thereby selecting certain attractors over others. The ideas of temporal difference learning and convergence of corticostriatal fibers from multiple cortical areas within the striatum are combined in a modular learning system capable of acquiring behavior with sequential structure.
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| 2. |
- Eriksson, David, et al.
(författare)
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Effects of short-term synaptic plasticity in a local microcircuit on cell firing
- 2003
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Ingår i: Neurocomputing. - : Elsevier BV. - 0925-2312 .- 1872-8286. ; 52-54, s. 7-12
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Tidskriftsartikel (refereegranskat)abstract
- Effects of short-term synaptic plasticity on cell firing properties in a microcircuit formed by a reciprocally connected pyramidal cell and FSN interneuron in layer 2/3 of neocortex were analyzed in a biophysical model. Induction of synaptic depression by backpropagating dendritic action potentials was replicated, as well as the resulting time dependent depression of IPSP amplitudes. Results indicate that the effect of the depression becomes significant above 30 Hz input frequency. The magnitude of the effect depends on the time constant of the dendritic calcium regulating the depression. The frequency range depends on the time constant of the IPSP.
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| 3. |
- Fransén, Erik, 1962-
(författare)
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Coexistence of synchronized oscillatory and desynchronized rate activity in cortical networks
- 2003
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Ingår i: Neurocomputing. - : Elsevier BV. - 0925-2312 .- 1872-8286. ; apr-52, s. 763-769
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Tidskriftsartikel (refereegranskat)abstract
- The basis of MRI and PET experiments is the finding that neuronal cell firing levels are modulated in a task dependent manner. Results from EEG and MEG experiments on the other hand point to the importance of synchrony, e.g. the peak frequency may depend on the difficulty of the task. In most models only one of these activity modes of firing is desirable or possible to produce. In this work we show how a cortical microcircuit can produce either synchronized or desynchronized firing, and how this solves problems of present day rate and synchronization models.
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| 4. |
- Fransén, Erik, 1962-, et al.
(författare)
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Entorhinal neuronal activity during delayed matching tasks may depend upon muscarinic-induced non-specific cation current I(CANM)
- 2001
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 38, s. 601-606
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Tidskriftsartikel (refereegranskat)abstract
- Biophysical compartmental models of stellate, pyramidal-like and interneurons in layer II of the rat entorhinal cortex were used to explore cellular and synaptic components involved in neuronal responses to stimuli in a delayed match to sample (DMS) task. Simulations demonstrate that the muscarinic receptor-induced non-specific cation current, I(CANM), could contribute to these phenomena. Facilitation of I(CANM) by calcium influx during spikes induced by the sample stimulus can cause enhanced responses for matches as well as delay activity. In a network, lateral inhibition can produce match suppression, and in conjunction with stimulus selective/non-selective cells produce non-match enhancement and suppression.
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| 5. |
- Hellgren Kotaleski, Jeanette, et al.
(författare)
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Sensitivity to interstimulus interval due to calcium interactions in the Purkinje cell spines
- 2002
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 44, s. 13-18
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Tidskriftsartikel (refereegranskat)abstract
- Pairing specific LTD (PSD) is produced by paired parallel fiber (PF) and climbing fiber (CF) stimulation and requires Ca2+ elevation. CF or PF activation cause Ca2+ increase through voltage dependent channels and IP3 induced Ca2+ release, respectively. We developed a model of Ca2+ dynamics in Purkinje cell spines to investigate why paired PF-CF activation is necessary for PSD. Simulations show a supralinear increase of the Ca2+ signal if the CF input occurs in a restricted time interval following the PF input. Ca2- buffers significantly contribute to this phenomenon. This mechanism may be involved in the requirement of temporal specificity in classical conditioning.
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| 6. |
- Hellgren Kotaleski, Jeanette, et al.
(författare)
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Simulation of metabotropic glutamate receptor induced effects in the lamprey CPG
- 2000
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 32, s. 433-439
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Tidskriftsartikel (refereegranskat)abstract
- Metabotropic glutamate receptor (mGluR) activation modulates the lamprey spinal locomotor network. Potentiation of the NMDA receptor current is observed suggesting that one possible mechanism for mGluR to regulate locomotion is through such an interaction. The present study investigates this possibility. The behavior of NMDA induced oscillations are explored when potentiation is achieved of different contributing factors of the NMDA receptor current. The effects on the duration of the depolarized phase as well as hyperpolarized interval depend on both level of activation and holding potential of the cells. From these effects on the cell level the network effects are predicted.
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| 7. |
- Huss, Mikael, et al.
(författare)
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Role of A-current in lamprey locomotor network neurons
- 2003
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Ingår i: Neurocomputing. - : Elsevier BV. - 0925-2312 .- 1872-8286. ; 52-54, s. 295-300
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Tidskriftsartikel (refereegranskat)abstract
- A compartmental model of lamprey central pattern generator neurons was built in order to examine the effects of a fast, transient, high-voltage-activated potassium current (A-current) found experimentally. The model consisted of a soma, a compartment corresponding to the axon initial segment, and a dendritic tree. The simulation showed that the A-current was necessary for repetitive spiking in the single neuron following current injection. The functional role of adding an A-current was also examined in a network model. In this model, the A-current stabilizes the swimming rhythm by making the burst cycle duration and the number of spikes per burst less variable. All these effects are also seen experimentally.
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| 8. |
- Kaipainen, Mauri, et al.
(författare)
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Period detection and representation by recurrent oscillatory self-organizing map
- 2003
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 55:3-4, s. 699-710
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Tidskriftsartikel (refereegranskat)abstract
- Whether or not periodicity is a property of the environment, for a cognitive system a period is always a dynamical mental construct. This study suggests a dynamical implementation of this hypothesis using recurrent oscillatory self-organizing map of the feature space of such streams. The mapping allows the system to assign identity and class-membership to each stream point, represented by a locus on a two-dimensional map. The model is shown to detect periodicities of various regular and behavior-originated, single- and multi-channel wave patterns, and to reproduce such signals, relying solely on the oscillating activation of the units.
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| 9. |
- Kozlov, Alexander, et al.
(författare)
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Burst dynamics under mixed NMDA and AMPA drive in the models of the lamprey spinal CPG
- 2003
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Ingår i: Neurocomputing. - : Elsevier BV. - 0925-2312 .- 1872-8286. ; 52-54, s. 65-71
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Kozlov, A. K., et al.
(författare)
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Modeling control of roll-plane body orientation in lamprey
- 2000
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Ingår i: Neurocomputing. - 0925-2312 .- 1872-8286. ; 32, s. 871-877
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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