What about the “Self” is Processed in the Posterior Cingulate Cortex?

A number of brain systems have been implicated in addictive behavior, but none have yet been shown to be necessary for maintaining the addiction to cigarette smoking. We found that smokers with brain damage involving the insula, a region implicated in conscious urges, were more likely than smokers with brain damage not involving the insula to undergo a disruption of smoking addiction, characterized by the ability to quit smoking easily, immediately, without relapse, and without persistence of the urge to smoke. This result suggests that the insula is a critical neural substrate in the addiction to smoking.

The structure of the human orbital and medial prefrontal cortex (OMPFC) was investigated using five histological and immunohistochemical stains and was correlated with a previous analysis in macaque monkeys [Carmichael and Price (1994) J. Comp. Neurol. 346:366-402]. A cortical area was recognized if it was distinct with at least two stains and was found in similar locations in different brains. All of the areas recognized in the macaque OMPFC have counterparts in humans. Areas 11, 13, and 14 were subdivided into areas 11m, 11l, 13a, 13b, 13m, 13l, 14r, and 14c. Within area 10, the region corresponding to area 10m in monkeys was divided into 10m and 10r, and area 10o (orbital) was renamed area 10p (polar). Areas 47/12r, 47/12m, 47/12l, and 47/12s occupy the lateral orbital cortex, corresponding to monkey areas 12r, 12m, 12l, and 12o. The agranular insula (areas Iam, Iapm, Iai, and Ial) extends onto the caudal orbital surface and into the horizontal ramus of the lateral sulcus. The growth of the frontal pole in humans has pushed area 25 and area 32pl, which corresponds to the prelimbic area 32 in Brodmann's monkey brain map, caudal and ventral to the genu of the corpus callosum. Anterior cingulate areas 24a and 24b also extend ventral to the genu of the corpus callosum. Area 32ac, corresponding to the dorsal anterior cingulate area 32 in Brodmann's human brain map, is anterior and dorsal to the genu. The parallel organization of the OMPFC in monkeys and humans allows experimental data from monkeys to be applied to studies of the human cortex. Copyright 2003 Wiley-Liss, Inc.

There is considerable uncertainty about the function of the posterior cingulate cortex (PCC). The PCC is a major node within the default mode network (DMN) and has high metabolic activity and dense structural connectivity to widespread brain regions, which suggests it has a role as a cortical hub. The region appears to be involved in internally directed thought, for example, memory recollection. However, recent nonhuman primate work provides evidence for a more active role in the control of cognition, through signaling an environmental change and the need to alter behavior. For an organism to flexibly react to a changing environment, information processed in functionally distinct brain networks needs to be integrated by such a cortical hub. If the PCC is involved in this process, its brain activity should show a complex and dynamic pattern that partially reflects activity in other brain networks. Using fMRI in humans and a multivariate analysis, we demonstrate that the PCC shows this type of complex functional architecture, where echoes of multiple other brain networks are seen in separable yet overlapping subregions. For example, a predominantly ventral region shows strong functional connectivity to the rest of the DMN, whereas two subregions within the dorsal PCC show high connectivity to frontoparietal networks involved in cognitive control. PCC subregions showed distinct patterns of activity modulation during the performance of an attentionally demanding task, suggesting that parts of the dorsal PCC interact with frontoparietal networks to regulate the balance between internally and externally directed cognition.