Oscillation, Chaos and Noise: From Shark Electroreceptors to Mental Disorders

Principle aspects of nonlinear dynamics in biological systems will be illustrated with examples from experimental, clinical and model data of different functions.
Experimental recordings of neuronal impulse trains and their simulation by mechanism-based mathematical models will be presented to demonstrate co-operative effects of nonlinear dynamics and noise. Special emphasis will be laid on impulse generation by subthreshold oscillations, including physiologically and pathophysiologically relevant transitions from pacemaker-like single-spike activity (tonic firing) to rhythmic impulse groups (bursts), including a broad range of chaotic impulse pattern.
Remarkably, similar concepts as for the modelling of neuronal impulse patterns can be used for the simulation of behavioural functions, e.g. sensitization and chronic progression of mental disorders. A few common principles, based on the combination of negative and positive feedback loops with different activation levels and time delays, can account for a high phenomenological diversity, suggesting a fractal dimension of biological functions. With a recently developed, neuron-based model of sleep-wake cycles, it will be demonstrated how the different functional levels and time-scales can be combined.