Consequences of deterministic and random dynamics for the course of affective disorders

Background: Uni- and bipolar affective disorders tend to be recurrent and p rogressive. Illness patterns can evolve from isolated episodes to more rapi d rhythmic, and "chaotic" mood patterns. Nonlinear deterministic dynamics a re currently proposed to explain this progression. However, most natural sy stems are nonlinear and noisy, and cooperative behavior of possible clinica l relevance can result. Methods: The latter issue has been studied with a mathematical model for pr ogression of disease patterns in affective disorders. Results: Deterministic dynamics can reproduce a progression from stable, to periodic, to chaotic patterns. Noise increases the spectrum of dynamic beh aviors, enhances the responsiveness to weak activations, and facilitates th e occurrence of aperiodic patterns. Conclusions: Noise might amplify subclinical vulnerabilities into disease o nset and could induce transitions Co rapid-changing dysrhythmic mood patter ns. We suggest that noise-mediated cooperative behavior, including stochast ic resonance, should be considered in appropriate models for affective illn ess. (C) 1999 Society of Biological Psychiatry.