Cognitive theories of recurrent depression suggest that the relationship between mood and cognition is altered by previous depressive episodes. In individuals remitted from depression (RMD) this would be linked to a larger susceptibility for new depressive symptoms. This study explored whether the association between mood and rumination indeed is different between RMD and non-depressed controls relying on dynamic systems theory (DST). From DST we selected entropy, defined here as the level of unpredictability in the relation between mood and rumination, as main variable of interest. Daily electronic dairy measures of mood and rumination were administered in 31 RMD patients and 32 healthy controls. The results indicate that mean levels of rumination and negative mood were elevated in RMD compared with controls. At the group level, entropy did not differ significantly and entropy was also not associated with the number of episodes. However, entropy predicted depressive symptoms in the RMD group and the brooding subtype of rumination in both groups at six months follow-up. These data are specific for entropy and were not obtained using mean levels of momentary mood and rumination.
