Self Comes to Mind

Brodmann’s cytoarchitectonic map, they are areas 23a/b, 29, 30, 31, and 7m.) The interconnectivity of these subregions is so intricate that it is reasonable, to some degree, to treat them as a functional unit. Some distinct connectional affiliations within the subsectors open the possibility that some of them may have distinct functional roles to play. The umbrella term we coined for the ensemble appears justified, at least for the time being.
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Figure 9.3 : The location of the posteromedial cortices in the human brain.
    The pattern of PMC connections, as reported in the first publication to come from these laborious and time-consuming investigations, 3 is summarized in Figure 9.4 . It can be described as follows:
    1. Inputs from parietal and temporal association cortices, entorhinal cortices, and frontal cortices converge in the PMCs, as do inputs from the anterior cingulate cortex (a principal recipient of projections from the insula), the claustrum, the basal forebrain, the amygdala, the premotor region, and the frontal eye fields. Thalamic nuclei, both intralaminar and dorsal, also project to the PMCs.
    2. With few exceptions, the sites that originate converging inputs to the PMCs also receive diverging outputs from them, exceptions being the ventromedial prefrontal cortex, the claustrum, and the intralaminar nuclei of the thalamus. Some sites that do not project to the PMCs do receive PMC projections, namely the caudate and putamen, the nucleus accumbens, and the periaqueductal gray.

     
Figure 9.4 : The pattern of neural connections to and from the posteromedial cortices (PMCs), as determined in a study conducted in the monkey. Abbreviations: dlpfc = dorsolateral prefrontal cortex; fef = frontal eye fields; vmpfc = ventromedial prefrontal cortex; bf = basal forebrain; claus = claustrum; acc = nucleus accumbens; amy = amygdala; pag = periaqueductal gray.
    3. There are no connections to or from the PMCs relative to the early sensory cortices or the primary motor cortices.
    4. From the results described under 1 and 2, it is apparent that the PMCs are a high-level convergence and divergence region. It is a prominent member of the club of CDRegions that I regard as good candidates for coordinating the contents in the conscious mind, and it even has an important connection with another potential coordinator, the claustrum, which significantly projects to the PMCs but is poorly reciprocated.
    A recent study conducted in humans has added support for the idea that the PMCs are neuroanatomically distinct. 4 The study, which was led by Olaf Sporns, used a modern technique of magnetic resonance imaging, diffusion spectrum imaging, which produces images of neural connections and of their approximate spatial distribution. The authors used their imaging data to construct maps of the connectional arrangements throughout the human cerebral cortex. They identified several connectional hubs throughout the cerebral cortex, several of which correspond to the CDRegions I have been discussing. They also concluded that the PMC region constitutes a unique hub, more strongly interrelated to other hubs than any of the others.
The PMCs at Work
     
    We are now in a better position to imagine how the PMCs might contribute to the conscious mind. Although this is a sizable portion of cerebral cortex, the power of the PMCs resides not with territorial possessions but with the company they keep. The PMCs receive signals from most high-order sensory association regions and premotor regions and largely return the favors. Brain areas rich in convergence-divergence zones, which hold the key to composites of multimodal information, are thus able to signal to the PMCs and by and large can be signaled back. The PMCs also receive signals from subcortical nuclei involved in wakefulness and in turn signal to a variety of subcortical regions related to attention and reward (in the brain stem and basal forebrain), as well as to regions capable of producing motor routines (such as the basal ganglia and the periaqueductal gray).
    What are the received signals likely to be about, and what do the PMCs do with them? We do not know for certain, but the huge disproportion between the profusion and strength of the projections toward the PMCs and the actual territory in which they land suggests an answer. The PMCs are mostly of older vintage, territories that one thinks of as holding dispositions rather than explicit maps. The PMCs are not modern early