Rumination is defined as ‘a mode of responding to distress that involves repetitively and passively focusing on symptoms of distress and on the possible causes and consequences of these symptoms’ (Nolen-Hoeksema et al., 2008). This tendency characterizes depression (Nolen-Hoeksema et al., 2008), and has been ascribed to deficient control processes that cannot rid memory of negative information (Joormann, 2005). As such, a growing literature has examined the relationship between depressive rumination and cognitive control during demanding cognitive tasks. However, it is likely that the most prominent display of rumination is not when people are engaged in a task, but when they are at rest. Examining how individuals with MDD and healthy controls (HCs) compare during such rest periods is important because interleaved with the ongoing tasks of life are significant periods in which people do not engage in structured tasks, and instead are left to mind-wander or ruminate. In fact, recent research indicates that people mind-wander _10–15% of their wakeful hours1 (Sayette et al., 2009). Neurally, mind-wandering appears to engage regions of a ‘default network’ (Christoff et al., 2009, Mason et al., 2007)_a set of neural regions that activate in unison during off-task or ‘rest’ periods, which include the posterior-cingulate, portions of lateral parietal cortex as well as portions of the medial temporal lobe (MTL) and medial prefrontal cortex (mPFC; Fox et al., 2005; Raichle, 2010; Shulman et al., 1997; Raichle et al., 2001). Recent research examining the default network has revealed striking differences between MDDs and HCs. MDDs show increased default-network connectivity (compared with HCs) with the subgenual-cingulate cortex (SCC), a region located in the mPFC, which is positively correlated with the length of MDDs’ current depressive episodes (Greicius et al., 2007). Other researchers have shown abnormalities in the subgenual cingulate for MDDs (Sheline et al., 2009; see Drevets et al., 2008 for a review), and this brain region has also been linked to poor emotion regulation (Abler et al., 2008) and is activated more when healthy young adults are induced to ruminate (Kross et al., 2009). Moreover, stimulation of white matter tracts leading to the subgenual cingulate in MDDs has been associated with remission of depression concomitant with a decrease in hyperactivity of the subgenual-cingulate itself (Mayberg et al., 2005). Even with all of this research, it is not clear what cognitive processes are reflected by these differences in defaultnetwork connectivity (Raichle, 2010). Although some researchers have speculated that this hyper-connectivity reflects rumination (Greicius et al., 2007), no research has directly tested this hypothesis. The first goal of the present research was to test whether default-network connectivity, particularly in the subgenual cingulate, is related to rumination.
References
Berman, Marc G., Scott Peltier, Derek E. Nee, Ethan Kross, Patricia J. Deldin, and John Jonides. 2011. “Depression, rumination and the default network.” Social cognitive and affective neuroscience 6 (5): 548–55. doi:10.1093/scan/nsq080.