A shared human experience is our active internal mental life. Left without an immediate task that demands full attention, our minds wander jumping from one passing thought to next—what William James (1890) called the “stream of consciousness.” We muse about past happenings, envision possible future events, and lapse into ideations about worlds that are far from our immediate surroundings. In lay terms, these are the mental processes that make up fantasy, imagination, daydreams, and thought….
While remembering, envisioning the future, and conceiving the mental states of others are different on several dimensions including temporal focus (e.g., past versus present) and personal perspective (e.g., self versus another person), they all converge on similar core processes (Buckner & Carroll 2007). In each instance, one is required to simulate an alternative perspective to the present. These abilities, which are most often studied as distinct, rely on a common set of processes by which mental simulations are used adaptively to imagine events beyond those that emerge from the immediate environment….
A central issue for our present purposes is to understand to what degree, if any, the default network mediates these forms of spontaneous cognition. The observation that the default network is most active during passive cognitive states, when thought is directed toward internal channels, encourages serious consideration of the possibility that the default network is the core brain system associated with spontaneous cognition[.]….Within this possibility, the default network plays a role in constructing dynamic mental simulations based on personal past experiences such as used during remembering, thinking about the future, and generally when imagining alternative perspectives and scenarios to the present….
Germane to this possibility, Hassabis and Maguire (2007) recently proposed that interactions among regions within the default network may “facilitate the retrieval and integration of relevant informational components, stored in their modality-specific cortical areas, the product of which has a coherent spatial context, and can then later be manipulated and visualized.” They refer to this process as “scene construction,” a term emphasizing that mental simulation often unfolds in one’s mind as an imagined scene with rich visual and spatial content (see also Hassabis et al. 2007).
Buckner, R. L., Andrews-Hanna, J. R., & Schacter, D. L. (2008). The brain’s default network: Anatomy, function, and relevance to disease. Annals of the New York Academy of Sciences, 1124, 1-38.