Schizophrenia as a Dynamical Disease

It is demonstrated that schizophrenia is a dynamical disease, i. e. that important aspects of schizophrenia can be understood on the basis of concepts of the theory of nonlinear dynamical systems. In particular, the gradual shift of a single parameter may result in completely different kinds of behavior of the entire system just like water can be in three qualitatively different states depending on the single parameter temperature. Transitions between these different states are called bifurcations or phase transitions. In case of schizophrenia the parameter may be the neurotransmitter dopamine (or serotonin or glutamate). With a high level of dopamine transmission the symptoms of schizophrenia appear, and with rather low levels those of Morbus Parkinson. In between a healthy state prevails. With respect to neuronal activity the effects of dopamine are demonstrated by a mathematical model which can be interpreted in two ways: on the one hand as a model of typical excitatory-inhibitory circuits in the cortex, on the other hand of a negative feedback loop between thalamus, prefrontal cortex and striatum. The model exhibits different types of firing patterns and their bifurcation, from various kinds of periodicities up to erratic or chaotic behavior, corresponding to different levels of dopamine concentration.