Noise, nonlinear dynamics and the timecourse of affective disorders

Affective disorders, such as depression or mania, tend to be recurrent and progressive. Typically, disease patterns evolve from isolated episodes to r hythmic and finally accelerated "chaotic" mood patterns during the longitud inal course. Concepts from dynamical systems have been considered to explai n this progression. However, most natural systems are not only nonlinear bu t also affected by noise. For this reason it seems important to incorporate cooperative stochastic-dynamic effects into current conceptional models fo r the course and neurobiology of such disorders. We use a computational per spective and describe behaviors of a simple mathematical model which result from interactions between random and deterministic dynamics. In particular , we Focus on a scenario for illness progression that relies on noise enhan cement of feedback instabilities. We suggest that noise amplification of su bclinical neurobiological vulnerabilities could represent a relevant diseas e mechanism. (C) 2000 Elsevier Science Ltd. All rights reserved.