Influence of positive feedback and noise on the responses of neurobiological sensitization systems

Sensitization means an increasing responsiveness after stimulation and represents a rather ubiquitous biological principle relevant for adaptation and mal-adaptation. We are interested in the basic mechanisms of sensitisation which underly longterm neuronal activity changes under normal and pathological conditions. For that, we recently have explored the dynamics of intrinsic oscillatory neurons engaged in positive feedback loops. The feedback loop becomes activated when a neuron spikes with the result of further excitation. The dynamics depend on the intrinsic properties of the respective neuron (including applied current or temperature range), the "synaptic" or "sensitization" strength, the associated time constant and external factors such as added noise. Dependent on the parameter region we find different periodic and chaotic spiking patterns with stable feedback behavior. As result of the chaotic dynamics of the model, the parametric range for stable spiking patterns is remarkably large. Implications for neurophysiology as well as pathological conditions will be discussed.

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