The existence of a “default mode” for brain function—an organized baseline mode that is suspended during specific goal-directed behaviors—has become established.1–4
It has recently been proposed that the core set of brain regions including cortical midline structures comprising the “default mode network” may also underlie certain high level human behaviors such as autobiographical memory, prospection, spatial navigation and imagination of another person's perspective (theory of mind,ToM) processes.5
A meta-analysis of neuroimaging studies found support for this proposal, showing a high degree of correspondence within the lateral prefrontal cotex, medial-temporal lobe, precuneus, posterior cingulate, retrosplenial cortex, the temporo-parietal junction and the occipital lobe across these domains.6
Another substantial cerebral network is the fronto-parietal mirror neuron system (MNS), which is active when an agent performs an action, but also when it observes that same action being performed by another agent. The MNS together with the “default network”, have been hypothesized to represent abstract and concrete aspects of the self, respectively, and interact to give rise to a unified representation of the self as a social being.7
It had been suggested in earlier work that areas of the default network may be involved in self-referential mental activity,8
and that this activity may represent the “projection of oneself into another time, place or perspective.”5
Thus, these lines of research on time, space, physical representations and social cognition appear to converge on a common set of brain regions, centered on the default mode network, as well as a set of cognitive processes that are anchored by the Self as point of reference.
Here, we would like to advance the proposal that the Self emerges as an integration of representations across the domains of time, space, physical embodiment and social cognition. Furthermore, the self-representation across all of these domains—time, space, physical and social—is accomplished through simulation. Simulation is a term that has been used in cognitive psychology to describe a variety of processes including Ingvar's “anticipatory programming” of behavior,9
estimates of likelihood of a behavior,10
the imitative representation of an event,11
“reenactments of sensory-motor states”12
and understanding the mental states of others.13
For our current purpose, we define simulation as the rather broad process of using existing representations as templates for processing novel information from one's own perspective. Essentially, this means humans use information that is already known, as a template for re-presenting and understanding new information, in order to plan our short- and long-term behaviors. In the following sections, we will briefly describe how this simulation process may subserve each of the domains constituting the Self—time, space, physical and social—and the brain regions supporting these re-presentations.