The Bernstein Center Freiburg




Informal Seminar
Christopher Kim

University of Minnesota


Computational model of the influence
of depolarization block on the initiation
of seizure-like activity

Under pathological conditions the interaction of excitatory and inhibitory (EI) neurons can become unbalanced, leading to seizure-like activity in the network. The interplay between excitatory and inhibitory neurons has been studied in rat hippocampal CA1, where spontaneous seizure-like activity was produced by blocking potassium ion channels and decreasing magnesium. The main finding from the study is that the excitatory neurons exhibit runaway excitation as the inhibitory neurons enter long-lasting depolarization block. In this study, we employ a modified Wilson-Cowan model to examine the dynamics of an EI network under similar pathological conditions. To model depolarization block, we modified the inhibitory population's activation function so that large input silences the population. Phase plane analysis shows that the network can be in as many as three different states, rest state, active state, and seizure state, where the inhibitory population enters depolarization block in the seizure state. The network can be bistable, where the rest and seizure state coexist, or if the external input to the inhibitory population is reduced, the network can become tristable, where all three state coexist for the same parameters. In addition, convergent connectivity structure from excitatory neurons onto inhibitory neurons is found to facilitate the transition to seizure state by reducing the strength of inhibitory drive when the network is near seizure state. The predictions of Wilson-Cowan model is tested with a network of Morris-Lecar (ML) neurons. We find that both bistable and tristable states are present in the ML network. Hysteresis is observed at the transitions between different states, providing evidence that the emergence of three states is a network phenomenon. It was also observed that the network enters seizure state at a low current input when the convergent connectivity structure is promoted.

Monday, August 4, 2014

16:00 h
BCF Library
First Floor
Hansastr. 9a
The talk is open to the public. Guests are cordially invited!
www.bcf.uni-freiburg.de