title: Major Depression as a Complex Dynamic System.
abstract: In this paper, we characterize major depression (MD) as a complex dynamic system in which symptoms (e.g., insomnia and fatigue) are directly connected to one another in a network structure. We hypothesize that individuals can be characterized by their own network with unique architecture and resulting dynamics. With respect to architecture, we show that individuals vulnerable to developing MD are those with strong connections between symptoms: e.g., only one night of poor sleep suffices to make a particular person feel tired. Such vulnerable networks, when pushed by forces external to the system such as stress, are more likely to end up in a depressed state; whereas networks with weaker connections tend to remain in or return to a non-depressed state. We show this with a simulation in which we model the probability of a symptom becoming 'active' as a logistic function of the activity of its neighboring symptoms. Additionally, we show that this model potentially explains some well-known empirical phenomena such as spontaneous recovery as well as accommodates existing theories about the various subtypes of MD. To our knowledge, we offer the first intra-individual, symptom-based, process model with the potential to explain the pathogenesis and maintenance of major depression.
authors.affiliation: Psychological Methods, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Angélique O J
authors.initials: AO
authors.lastname: Cramer
authors.affiliation: Psychological Methods, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Claudia D
authors.initials: CD
authors.lastname: van Borkulo
authors.affiliation: Department of Psychiatry, Leids Universitair Medisch Centrum, Leiden, the Netherlands.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Giltay
authors.affiliation: Psychological Methods, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Han L J
authors.initials: HL
authors.lastname: van der Maas
authors.affiliation: Virginia Institute of Psychiatric and Behavioral Genetics, Virginia Commonwealth University, Richmond, Virginia, United States of America.
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Kendler
authors.affiliation: Department of Aquatic Ecology, Wageningen University, Wageningen, the Netherlands.
authors.forename: Marten
authors.initials: M
authors.lastname: Scheffer
authors.affiliation: Psychological Methods, University of Amsterdam, Amsterdam, the Netherlands.
authors.forename: Denny
authors.initials: D
authors.lastname: Borsboom
mesh_terms: D003865:Major Depressive Disorder / Q000503:physiopathology*; D006801:Humans; D008962:Models, Theoretical