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This article is part of the supplement: Twentieth Annual Computational Neuroscience Meeting: CNS*2011

Open Access Poster presentation

Dynamics of self-sustained activity in random networks with strong synapses

Håkon Enger1*, Tom Tetzlaff1, Birgit Kriener1, Marc-Oliver Gewaltig23 and Gaute T Einevoll1

Author Affiliations

1 Dept. of Mathematical Sciences and Technology, Norwegian University of Life Sciences, NO-1432 Ås, Norway

2 Honda Research Institute Europe GmbH, D-63073 Offenbach/Main, Germany

3 Bernstein Center for Computational Neuroscience, D-79104 Freiburg, Germany

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BMC Neuroscience 2011, 12(Suppl 1):P89  doi:10.1186/1471-2202-12-S1-P89


The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1471-2202/12/S1/P89


Published:18 July 2011

© 2011 Enger et al; licensee BioMed Central Ltd.

This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Poster presentation

An understanding of short-term memory requires models of neural networks which are able to sustain activity in the absence of external input for several seconds. About half a century ago, [1] predicted the existence of self-sustained activity in neural networks with strong synapses. Despite this finding, most previous studies on the dynamics of neural networks are restricted to weak synapses, i.e. to a regime where the diffusion approximation is applicable. Recently, it has been shown in simulations that self-sustained activity emerges in networks of integrate-and-fire (IaF) neurons with strong synapses modeled as currents [2] (rather than as conductances, see [3]). Above a critical synaptic weight, the lifetime of self-sustained activity increases rapidly (Fig. 1C). We present a stochastic model of the dynamics of a balanced random network of IaF neurons with current-based synapses in the strong-synapse regime. Based on the network's firing-rate transfer [4], we show that the firing-rate dynamics becomes bistable if the synapses are sufficiently strong: in addition to the quiescent state, a second stable fixed point at moderate firing rates is created (sketched in Fig. 1A). Firing-rate fluctuations can destabilize this fixed point, thereby limiting the lifetime of self-sustained activity (sketched in Fig. 1B). The magnitude of these fluctuations is mainly determined by the amount of spike-train correlations [5]. Our model explains the existence and the lifetime of self-sustained activity, and how the lifetime depends on the network size, the connectivity, the level of inhibition and the synapse strength. The results of our model are confirmed by network simulations.

thumbnailFigure 1. A. Phase space of the firing-rate dynamics. Dependence of the rate change dr/dt on the rate r (sketch). B. Firing-rate distribution in the self-sustained state (sketch). C. Dependence of the lifetime of self-sustained activity (color coded) on the level g of inhibition and the synaptic weight J in a random network of 100000 excitatory and 25000 inhibitory IaF neurons with 1% connectivity (simulation results).

Acknowledgements

We acknowledge support by the NOTUR and eScience programs of the Research Council of Norway. All network simulations were carried out with the neural simulation tool NEST (see http://www.nest-initiative.org).

References

  1. Griffiths JS: On the stability of brain-like structures.

    Biophys J 1963, 3:299-308. PubMed Abstract | Publisher Full Text | PubMed Central Full Text OpenURL

  2. Gewaltig M: Self-sustained activity in networks of integrate and fire neurons without external noise.

    Front. Comput. Neurosci. Conference Abstract: Bernstein Conference on Computational Neuroscience 2009.

    doi: 10.3389/conf.neuro.10.2009.14.051

    OpenURL

  3. Kuhn A, Aertsen A, Rotter S: Neuronal integration of synaptic input in the fluctuation-driven regime.

    J Neurosci 2004, 24(10):2345-2356. PubMed Abstract | Publisher Full Text OpenURL

  4. Siegert AJF: On the first passage time probability problem.

    Phys Rev 1951, 81:617-623. Publisher Full Text OpenURL

  5. Kriener B, Tetzlaff T, Aertsen A, Diesmann M, Rotter S: Correlations and population dynamics in cortical networks.

    Neural Comput 2008, 20:2185-2226. PubMed Abstract | Publisher Full Text OpenURL