Helmut Schmidt

University of Nottingham, Nottigham, England, United Kingdom

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Publications (4)6 Total impact

  • Source
    Stephen Coombes, Helmut Schmidt, Ingo Bojak
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    ABSTRACT: Neural field models describe the coarse-grained activity of populations of interacting neurons. Because of the laminar structure of real cortical tissue they are often studied in two spatial dimensions, where they are well known to generate rich patterns of spatiotemporal activity. Such patterns have been interpreted in a variety of contexts ranging from the understanding of visual hallucinations to the generation of electroencephalographic signals. Typical patterns include localized solutions in the form of traveling spots, as well as intricate labyrinthine structures. These patterns are naturally defined by the interface between low and high states of neural activity. Here we derive the equations of motion for such interfaces and show, for a Heaviside firing rate, that the normal velocity of an interface is given in terms of a non-local Biot-Savart type interaction over the boundaries of the high activity regions. This exact, but dimensionally reduced, system of equations is solved numerically and shown to be in excellent agreement with the full nonlinear integral equation defining the neural field. We develop a linear stability analysis for the interface dynamics that allows us to understand the mechanisms of pattern formation that arise from instabilities of spots, rings, stripes and fronts. We further show how to analyze neural field models with linear adaptation currents, and determine the conditions for the dynamic instability of spots that can give rise to breathers and traveling waves.
    Journal of mathematical neuroscience. 05/2012; 2(1):9.
  • Source
    Helmut Schmidt, Ingo Bojak, Stephen Coombes
    BMC Neuroscience 01/2010; · 3.00 Impact Factor
  • Source
    Stephen Coombes, Helmut Schmidt
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    ABSTRACT: Many tissue level models of neural networks are written in the language of nonlinear integro-differential equations. Analytical solutions have only been obtained for the special case that the nonlinearity is a Heaviside function. Thus the pursuit of even approximate solutions to such models is of interest to the broad mathematical neuroscience community. Here we develop one such scheme, for stationary and travelling wave solutions, that can deal with a certain class of smoothed Heaviside functions. The distribution that smoothes the Heaviside is viewed as a fundamental object, and all expressions describing the scheme are constructed in terms of integrals over this distribution. The comparison of our scheme and results from direct numerical simulations is used to highlight the very good levels of approximation that can be achieved by iterating the process only a small number of times.
    01/2010;
  • Source
    Helmut Schmidt, Stephen Coombes
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    ABSTRACT: or> Meeting abstracts - A single PDF containing all abstracts in this Supplement is available
    BMC Neuroscience 01/2009; · 3.00 Impact Factor

Publication Stats

14 Citations
6.00 Total Impact Points

Top Journals

Institutions

  • 2009–2010
    • University of Nottingham
      • School of Mathematical Sciences
      Nottigham, England, United Kingdom