The default network is activated by diverse forms of tasks that require mental simulation of alternative perspectives or imagined scenes. Four such examples from the literature illustrate the generality. (A) Autobiographical memory: subjects recount a specific, past event from memory. (B) Envisioning the future: cued with an item (e.g., dress), subjects imagine a specific future event involving that item. (C) Theory of mind: subjects answer questions that require them to conceive of the perspective (belief) of another person. (D) Moral decision making: subjects decide upon a personal moral dilemma. Note that all the studies activate strongly PCC/Rsp and dMPFC. Active regions also include those close to IPL and LTC, although further research will be required to determine the exact degree of anatomic overlap. It seems likely that these maps represent multiple, interacting subsystems.
The current set of analyses provides converging evidencethat DMN regions are engaged with specific cognitive behaviors. These behaviors may not be limited to those observed here, but may also include related processes such as moral decision-making (Greene, Sommerville, Nystrom, Darley, & Cohen, 2001), fictional narrative simulation (Mar & Oatley, 2008; Mar, 2004), or mind-wandering (Christoff, Gordon, Smallwood, Smith, & Schooler, 2009; Mason et al., 2007). In order to determine the neural (in)dependence of these processes, however, neuropsychological investigations into co-occurring autobiographical and interpersonal deficits with compromised functional integrity of the midline, and lateral parietal and lateral temporal cortex are also necessary.Our analyses were designed to investigate the neural mechanisms underlying autobiographical memory, prospection, and theory-of-mind, and to determine if thesedomains rely upon a pattern of brain activity operating within the DMN. The results provide the first direct evidence to support previous independent observation that projection of the self into the past, the future, or the minds of others, engages a common set of brain regions largely overlapping with the DMN (Spreng et al., 2009; Buckner & Carroll, 2007).(...)The present set of analyses provides converging evidence that the neuroanatomical correlates of autobiographical memory, prospection, and theory-of-mind are shared and that the DMN is involved in the processing necessary to carry out these specific cognitive behaviors. This sharing of neural resources may allow remembering the past and imagining the future to providea “long view” in decision-making, over and above stimulus–reward driven behavior, thereby facilitating theory-of-mind and promoting social cooperation (Boyer, 2008).