Self Comes to Mind

Coordinators
     
    In the working hypothesis presented here, the first stage of the implementation of the neural autobiographical self requires structures and mechanisms already discussed for the core self. But there is something distinctive about the structures and mechanisms needed to implement the second stage of the process, namely, the brain-wide coordination described earlier.
    What are the candidates for this large-scale system-coordination role? Several possible structures come to mind, but only a few can be seriously considered. An important candidate is the thalamus, a perpetual presence in any discussion of the neural basis of consciousness, specifically its collection of associative nuclei. The intermediate position of the thalamic nuclei, between the cerebral cortex and the brain stem, is ideal for signal brokering and coordination. Although the associative thalamus is busy enough constructing the background fabric of any image, it plays a very important, albeit perhaps not the lead, role when it comes to coordinating the contents that define the autobiographical self. I will say more about the thalamus and coordination in the next chapter.
    What are the other likely candidates? A strong contender is a composite collection of regions in both cerebral hemispheres that is distinguished by its connectional architecture. Each region is a macroscopic node located at a major crossroads of convergent and divergent signaling. I described them as convergence-divergence regions or CDRegions in Chapter 6 and indicated that they are made of numerous convergence-divergence zones. CDRegions are strategically located within high-order association cortices but not within the image-making sensory cortices. They surface in sites such as the temporoparietal junction, the lateral and medial temporal cortices, the lateral parietal cortices, the lateral and medial frontal cortices, and the posteromedial cortices. These CDRegions hold records of previously acquired knowledge regarding the most diverse themes. The activation of any of these regions promotes the reconstruction, by means of divergence and retroactivation into image-making areas, of varied aspects of past knowledge, including those that pertain to one’s biography, as well as those that describe genetic, nonpersonal knowledge.

     
Figure 9.2: The task of coordinating the varied images generated by ongoing perception and recall is assisted by convergence-divergence regions (CDRegions), which are located within the nonmapped association cortices. The approximate location of the main CDRegions is suggested in the diagram (darkly shaded areas): the polar and medial temporal cortices, the medial prefrontal cortices, the temporoparietal junctions, and the posteromedial cortices (PMCs). In all likelihood, there are other such regions. Most of the CDRegions depicted in the figure are also part of Raichle’s “default network” discussed later in this chapter. See Chapter 6 and Figures 6.1 and 6.2 for the architecture of these regions. See Figure 9.4 for connectional details of one CDRegion, the PMCs.
    Conceivably, the main CDRegions could be further integrated by long-range cortico-cortical connections of the kind first identified by Jules Déjérine a century ago. Such connections would introduce yet another level of interareal coordination.
    One of the main CDRegions, the posteromedial cortices (PMCs), appears to have a higher functional hierarchy relative to the others and exhibits several anatomical and functional traits that distinguish it from the rest. A decade ago I suggested that the PMC region was linked to the self process, albeit not in the role I now envision. Evidence obtained in recent years suggests that the PMC region is indeed involved in consciousness, quite specifically in self-related processes, and has provided previously unavailable information regarding the neuroanatomy and physiology of the region. (The evidence is discussed in the last sections of this chapter.)
    The final candidate is a dark horse, a mysterious structure known as the claustrum, which is closely related to the CDRegions. The claustrum, which is located between the insular cortex and the basal ganglia of each hemisphere, has cortical connections that might potentially play a coordinating role. Francis Crick was convinced that the claustrum was a sort of director of sensory operations charged with binding disparate components of a multisensory percept. The evidence from