The coexistence of depressive symptoms and cognitive decline in older adulthood is well established, whereby greater depressive symptoms are associated with poorer cognitive functioning and cognitive decline (Dotson, Resnick, & Zonderman, 2008). However, the causal and temporal relations between depressive symptoms and cognition remain ill-defined. There are suggestions that depressive symptoms may increase an individual's risk for subsequent cognitive decline. For example, there are reports that those with more baseline depressive symptoms had greater cognitive decline over time than those without depressive symptoms (Kohler et al., 2010; Yaffe et al., 1999). Another study found no increase in depressive symptoms during the prodromal phase of Alzheimer's disease (AD; Wilson, Arnold, Beck, Bienias, & Bennett, 2008), and concluded that depression acts to change cognition, and not the other way around. In contrast, lower cognitive functioning may increase the risk for depressive symptoms. Studies that have found depressive symptoms were unrelated to the rate of cognitive decline (Ganguli, Yangchun, Dodge, Ratcliff, & Chang, 2006; Vinkers, Gussekloo, Stek, Westendorp, & van der Mast, 2004) have consequently concluded that the alternative directional explanation (i.e., cognitive decline leads to depressive symptamotology) is more probable. Thus the connection between aspects of depression and cognition remains equivocal. Further, it may not be best expressed by a simple unidirectional temporal pathway. Han and colleagues (2006) attributed the link between depressive symptoms and general cognitive functioning to short-term situational factors, in that the relation is concurrent or temporary, rather than leading to increased risk. Alternatively, Jorm (2000) noted various hypotheses concerning the common coexistence of depressive symptoms and dementia including other conceptualizations such that depression and dementia share common risk factors (e.g., vascular disease). Nonetheless, we restrict our focus to the time-ordered relation between depressive symptoms and cognitive decline. Insight into the directionality of this association will aid in understanding whether and how their interrelation develops over time, and possibly provide key information into the disease process of dementia and major depression. Although longitudinal analysis has informed our understanding of covariation between depressive symptoms and cognitive decline (Chen, Ganguli, Mulsant, & DeKosky, 1999; Ganguli et al., 2006; Han et al., 2006; Vinkers et al., 2004; Yaffe et al., 1999), there has been no direct test of the directionality of the relation whereby a dynamic association is allowed to occur across time, or where one variable is modeled as being related to change in the other variable over time. With recent advances in statistical modeling, the bivariate dual change score model (BDCSM, McArdle & Hamagami, 2001) indeed allows for such temporal comparisons. This model is based in a structural equation modeling framework, and builds upon the latent growth curve model which estimates latent intercept and slope factors at the population level. The BDCSM allows for examining time-ordered associations between two constructs, thereby testing whether one variable at a given point in time predicts subsequent change in the other variable (see Figure 1). This model has been successfully applied to empirically test associations among other psychological domains, including competing hypotheses about the nature of lead-lag associations between cognition and leisure activities (Lovden, Ghisletta, & Lindenberger, 2005), cognition and well-being (Gerstorf, Lovden, Rocke, Smith, & Lindenberger, 2007), and the dynamic associations of cognitive functioning between spouses (Gerstorf, Hoppmann, Anstey, & Luszcz, 2009). 1 Graphical representation of a two-variable Dual Change Score Model (DCSM(McArdle & Hamagami, 2001)) for a system of two variables X and Y. Observed (manifest) variables are represented by squares, unobserved (latent) variables by circles, regression ... In this study, we applied the BDCSM to 15-year longitudinal data of depressive symptoms and perceptual speed. Perceptual speed was selected as the marker of cognitive functioning, as it constitutes the limiting factor for other cognitive processes (Luszcz & Bryan, 1999) and is a highly reliable and sensitive marker of cognitive change throughout adulthood (Anstey, Hofer, & Luszcz, 2003; Salthouse, 2004). By simultaneously modeling longitudinal changes in depressive symptoms and cognition, we tested various hypotheses about their dynamic relation over time. First, we investigated both unidirectional hypotheses: whether the level of depressive symptoms at time [t] predicts subsequent change in perceptual speed between [t] and [t + 1], or whether the level of perceptual speed predicts changes in depressive symptomatology. Next, we analyzed bidirectional associations, including where both leading pathways exist and are of different magnitude, and where neither variable is associated with changes in the other. Finally, we covaried the effects of baseline age, education, general cognitive status, and number of medical conditions to ensure our findings do not simply reflect the influence of these variables on cognitive functioning and depressive symptoms (Bassuk, Berkman, & Wypij, 1998; Geerlings et al., 2000).