Self Comes to Mind

sensory cortices like those of vision or hearing, where detailed maps of things and events can be assembled. Let us say that the PMC gallery has not enough wall space to exhibit large paintings or, for that matter, to present puppet shows. But that is just fine because the cortices that signal to the PMCs are not like early sensory cortices either; they cannot exhibit large paintings or present puppet shows any more than the PMCs can; they too are largely dispositional, convergence-divergence zone holders of recorded information.
    Given their design, the PMCs as a whole and their component sub-modules are likely to behave as convergence-divergence regions themselves. I envision that the information held by the PMCs as well as by their partners can be played back only by signaling back into other CDRegions in the club, which in turn can signal to early sensory cortices. Those are the cortices where images can be made and displayed—that is, where large paintings can be shown and puppet shows presented. Relative to the other convergence-divergence regions that interconnect with them, the PMCs have a special hierarchical rank. The PMC region sits higher on the totem pole, capable of interactive signaling with the other CDRegions.
    How, then, does the PMC assist consciousness? By contributing to the assembly of autobiographical self states. This is what I envision: separate sensory and motor activities related to personal experience would have been originally mapped in the appropriate brain regions, cortically and subcortically, and the data recorded in convergence-divergence zones and in convergence-divergence regions. In turn, the PMCs would have constituted a higher-order CDRegion record interconnected with the other CDRegions. The arrangement would allow activity in the PMCs to access larger, highly distributed data sets, but with the advantage that the access command would come from a relatively small and thus spatially manageable territory. The PMCs could support the establishment of momentary and temporally cohesive displays of knowledge.
    If the PMCs’ pattern of neuroanatomical connections is noteworthy, so is their anatomical location. The PMCs are located near the midline, the left set looking across the interhemispheric divide at the right set. This geographic position within the brain volume is convenient for both convergence and divergence connectivity relative to most regions of the cortical mantle, and it is ideal for receiving signals from the thalamus and reciprocating them. Curiously, the location also affords protection from external impact, and, because it is supplied by three major and separate blood vessels, it makes the PMCs relatively immune to the sort of vascular damage or trauma that could radically destroy them.
    As I have previously emphasized, consciousness-related structures share several anatomical traits. First, either at the subcortical or the cortical level, they tend toward the old vintage. This should not be surprising given that the beginnings of consciousness occurred late in biological evolution but are not at all a recent evolutionary development. Second, both cortical and subcortical structures tend to be placed at or near the midline, and, just like the PMCs, they like to look at their twin siblings across the brain’s midline—this is the case with thalamic and hypothalamic nuclei, as well as with brain-stem tegmental nuclei. Evolutionary age and convenience of location relative to widespread signal distribution are closely correlated here.
    The PMCs would operate as a partner to the network of cortical CDRegions. But the role of the other CDRegions and the importance of the protoself system is such that consciousness is likely to be affected but not abolished following the hypothetical destruction of the entire PMC region, provided all the other CDRegions and the protoself system remain intact. Consciousness would be restored, albeit not at its peak. The situation of late-stage Alzheimer’s disease, which I describe in the next section, is different in the sense that the PMC insult is virtually the last straw in a process of gradual ravage that has already disabled other CDRegions and the protoself system.
Other Considerations on the Posteromedial Cortices
     
ANESTHESIA RESEARCH
    In some respects, general anesthesia is an ideal means to investigate the neurobiology of consciousness. It is one of the most spectacular developments of medicine and has saved the lives of