Introduction

Using nonlinear dynamical systems (NDS) theory and methodologies within psychopathology research is a relatively recent development, with roots in various disciplines ranging, at least, from biology to psychiatry and psychology. Some early work on schizophrenia and catatonia (Danziger & Elmergreen, 1954; Gjessing, 1932) already elaborated mathematical models of psychopathological conditions, by which these authors approximated what would later be known as the dynamical disease approach (Mackey & Glass, 1977; Wehr & Goodwin, 1979). Gestalt psychiatry (Goldstein, 1934/1995; Matussek, 1952) may be viewed as a predecessor of contemporary complexity theory as it applied the holistic concepts of Gestalt psychology to mental disorders. Fields within biology such as chronobiology (Winfree, 1980) provided additional, independent developments that were more explicitly based on dynamical systems theory.

Psychopathology theory and research has focused on a number of properties of NDS, such as stability, deterministic chaos, and complexity. From a phenomenological point of view, these properties appear to have little in common. In a majority of applications the focus was put on the asymptotic stability of systems dynamics because stability and homeostasis are easily accessible in empirical research. Chaos theory, on the other hand, has placed an emphasis on the nonpredictability and erratic nature of some nonlinear systems (Freeman, 1992; Guastello, 1995). Complexity theory addressed still another phenomenon, the reduction of degrees of freedom that characterizes self-organizing systems; if certain prerequisites are given (i.e., if complex systems dwell in an environment far from thermodynamic equilibrium), in which collective parameters entrain the behavior of the microscopic elements of a system (Haken, 1977).