One of the most consistent observations in individual functional imaging is

One of the most consistent observations in individual functional imaging is a network of human brain locations known as the default network boosts it is activity during passive state governments. the default network, was originally noticed during passive, experimental control tasks included in a variety of studies (Shulman et al., 1997; Mazoyer et al., 2001). Raichle 1000023-04-0 IC50 and colleagues (Raichle et al., 2001; Gusnard and Raichle, 2001) drew attention to the network and suggested that its ubiquitous appearance in default says signals an essential, adaptive function. The network has since received growing attention because of its alteration in neurological and psychiatric disorders (Buckner et al., 2008; Broyd et al., 2009). However, despite the widespread interest there has not been consensus around the default network’s functions or even whether its presence signifies an adaptive contribution to cognition (Gilbert et al., 2007; Morcom and Fletcher, 2007). The present series of studies sought to resolve these discrepancies by dissecting its anatomy and function. Possible functions of the default network are 1000023-04-0 IC50 suggested by two sources of evidence. The first source comes from studies of directed tasks that cause activity increases in regions within the default 1000023-04-0 IC50 network. Anatomically, the default network comprises regions along the anterior and posterior midline, the lateral parietal cortex, and the medial temporal lobe (Buckner et al., 2008). Tasks that encourage subjects toward internal mentation, including autobiographical memory, thinking about one’s future, theory of mind, self-referential and affective decision making tend to activate regions within the default network (reviewed in Oschner et al., 2004; Buckner et al., 2008; Spreng et al., 2009). What processing demands are shared in common across these tasks is presently unclear. A challenge to the field has been to disentangle such high level tasks into component processes. Some have suggested a role for components of the default network in scene construction (Hassabis and Maguire, 2007), contextual associations (Bar, 2007), and conceptual processing (Binder et al., 2009). Others have suggested a role for the default network in interpersonal (Mitchell, 2006; Shilbach et al., 2008), self-referential or affective cognition (Gusnard et al., 2001; Wicker et al., 2003; D’Argembeau et al., 2005; in press) with minimal emphasis on mnemonic or prospective processes (but see D’Argembeau et al., in press). Schacter and Addis (2007) highlighted that future-oriented thoughts, which strongly drive activity in the default network, are inherently constructive, building on multiple episodic memories. They further argued that mental simulation based on memory is a core process of future-oriented cognition (Schacter et al., 2007). The divergence across these perspectives, perhaps exemplified best by the different emphases in Hassabis and Maguire’s scene construction model (Hassabis and Maguire, 2007) and D’Argembeau et al’s emphasis on self-referential cognition (D’Argembeau et al., 2005; in press), suggests the default network likely comprises multiple interacting subsystems (e.g., Hassabis et al., 2007a; Buckner et al., 2008). The 1000023-04-0 IC50 second source of evidence about the function of the default network comes from examination of what people think about during passive task states. Associations between default network activity and spontaneous thoughts have emerged in multiple studies (e.g. McKiernan et al., 2006; Mason et al., 2007; Christoff et al., 2009). In terms of content, individuals report spontaneously thinking about personally significant or concerning events (Singer, 1966; Klinger, 1971), a considerable portion of which possess a future orientation (Andreasen et al., 1995; Andrews-Hanna 1000023-04-0 IC50 et al., 2008, submitted). Other researchers have emphasized the interpersonal aspects of spontaneous thought (Mitchell, 2006; Shilbach et al., 2008). Despite these observations, it remains unclear why the specific regions within the default network activate together during passive epochs and how they might support the kinds of internal mentation reported by participants. In this paper we conducted a detailed characterization of the architecture of the default network using analysis of intrinsic connectivity combined with graph-analytic and clustering techniques. Next, task-based functional MRI (fMRI) was employed to explore the differential contributions of the component systems comprising the default network. Participants made decisions GSN about themselves in the future with task variations constructed to selectively minimize self-referential processing or the demand for construction of an imagined scene. As the results will reveal, the task variations differentially modulated distinct components of the default network. We further examined the functions of the dissociated components by exploring the nature of strategies used during each task trial. These dissociated components contribute differentially to two processes common during spontaneous thought: construction of imagined events and assessment of their personal significance. Results Experiment 1 The default network comprises two subsystems that interact with a common.