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1

Susceptibility of switching between in-phase and anti-phase patterns in the network of relaxation oscillators

Olejarczyk E., Ostaszewski H., Meyrand P., Bem T.

Biocybernetics and Biomedical Engineering

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2014

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Vol. 34, no. 4

250--257

EN

Neural networks composed of two or four cells with combined, electrical and inhibitory, synapses and realized for various network topologies were examined. The aim of this study was to determine a set of phases of oscillatory cycle in which different patterns of activity, characteristic for such networks, can be switched under an external stimulus. In particular, we studied susceptibility of switching between in-phase (IP) and anti-phase (AP) patterns (and vice versa). Our results demonstrate that windows of switching between patterns are similar for networks with electrical and mixed synapses and, in general, relatively independent of the network topology. The only effect of the network topology is an increase of the robustness of the AP pattern in networks of ring-like connectivity. The switching window width and thereby the robustness of the transitions between patterns decreases with the increase of the electrical coupling strength.

2

Multi-stability of in-phase and anti-phase activity patterns in neural networks with inhibitory and electrical synapses

Ostaszewski H., Meyrand P., Branchereau P., Hallam J., Bem T.

Biocybernetics and Biomedical Engineering

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2010

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Vol. 30, no. 3

3-17

EN

As shown in modeling and experimental studies, network comprised of spiking cells interconnected by inhibitory and electrical synapses may express different activity patterns without any change of the network topology or parameters. In this study we confirm robust-ness of this phenomenon by demonstrating multi-stability of hybrid networks consisting of biological neurons of different types. Moreover we show here, using relaxation oscillator model cells, that multi-stability of in-phase (IP) and anti-phase (AP) patterns may be expressed in a network fully connected by instantaneous synaptic inhibition and electrical coupling independently of the network size. In such a network a stimulus of a given profile, consisting of depolarizing and hyperpolarizing signals sent to different subpopulations of cells, can evoke direct switching between IP and AP patterns. We also show that similar phenomenon occurs in more realistic network models with sparse connectivity. Our results suggest that transient signals if arriving in a proper time window may instantaneously reconfigure a given spatio-temporal activity pattern expressed by the network into another stable pattern without any change of the network properties.

3

Significance of the neuronal morphology for network dynamics

Meyrand P.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 2

15-23

EN

One of the striking features of the Nervous System is the complexity and diversity of the neuronal shapes. Extensive morphological studies associated with modeling approaches have emphasized a close relationship between the neuron structure and its bioelectrical properties. However, structural implications of the synaptic connectivity (spatial distribution, number of synapses) in the context of the network operation are far less studied. To explore this issue, the chemical inhibitory synapses between identified motoneurones belonging to the stomatogastric nervous system of the lobster Homarus gammarus were examined. Using multiple intracelIular dyes injected in both pre- and post synaptic motoneurones, the sites of the appositions between these two celIs were localized under the laser-scanning confocal microscopy, and then the synaptic release sites were visualized under the electron microscopy. Such analysis indicates that only one or two zones of apposition exist between the two celIs studied, and only one release site exists per zone. Moreover, these synaptic sites are always located in the same position within the dendritic arbor. Modeling studies suggest that such a specific localization may play an important role in the operation of the network.

4

Electrical coupling and bistability in inhibitory neuronal networks

Bem T., Hallam J., Meyrand P., Rinzel J.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 2

3-14

EN

The role of gap junction-mediated electrical coupling in oscillatory networks is not yet fuIly understood. Such coupling is widespread in developing nervous systems and in many structures of the adult brain where it coexists with synaptic inhibition. Our results, both modeling and experimental, indicate that the effect of electrical coupling in networks of rhythmic inhibitory neurons is crucially dependent on the cells' duty cycle. In the Stomatogastric Nervous System, in which ceIls with large duty cycle are interconnected by reciprocal inhibition, electrical coupling may be responsible for masking adult-like properties of the embryonic network by coordinating the neuronal activity into a single rhythm with different phases. In a two-ceIl half-center oscillator model short duty cycle destabilizes antiphase activity which can be re-established by adding electrical coupling. Moreover, such a network expresses bistability of the in-phase and anti-phase patterns in some range of coupling strengths. AIso in a large-scale model network, in which ceIls are interconnected electrically and by synaptic inhibition, multistability of the in-phase and different anti-phase patterns may occur. A possible function of the multistability in the controI of movement is discussed.