Posterior cingulate, precuneal and retrosplenial cortices: cytology and components of the neural network correlates of consciousness - PubMed (original) (raw)

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Posterior cingulate, precuneal and retrosplenial cortices: cytology and components of the neural network correlates of consciousness

Brent A Vogt et al. Prog Brain Res. 2005.

Abstract

Neuronal aggregates involved in conscious awareness are not evenly distributed throughout the CNS but comprise key components referred to as the neural network correlates of consciousness (NNCC). A critical node in this network is the posterior cingulate, precuneal, and retrosplenial cortices. The cytological and neurochemical composition of this region is reviewed in relation to the Brodmann map. This region has the highest level of cortical glucose metabolism and cytochrome c oxidase activity. Monkey studies suggest that the anterior thalamic projection likely drives retrosplenial and posterior cingulate cortex metabolism and that the midbrain projection to the anteroventral thalamic nucleus is a key coupling site between the brainstem system for arousal and cortical systems for cognitive processing and awareness. The pivotal role of the posterior cingulate, precuneal, and retrosplenial cortices in consciousness is demonstrated with posterior cingulate epilepsy cases, midcingulate lesions that de-afferent this region and are associated with unilateral sensory neglect, observations from stroke and vegetative state patients, alterations in blood flow during sleep, and the actions of general anesthetics. Since this region is critically involved in self reflection, it is not surprising that it is similarly a site for the NNCC. Interestingly, information processing during complex cognitive tasks and during aversive sensations such as pain induces efforts to terminate self reflection and result in decreased processing in posterior cingulate and precuneal cortices.

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Figures

Figure 1

Figure 1

A. Co-registration of Brodmann’s map of posterior cingulate and precuneal cortices and a postmortem case for joint histological assessment. Stroked dots outline the border of cingulate cortex and four numbered arrows refer to locations of particular Brodmann areas discussed in the text. Brodmann’s actual numbers 23 and 31 are shown in the co-registration, while all other numbers refer to Vogt et al. (2005). The arrow at 4. points to the level of the coronal histological section taken for B. A critical issue at 4. is the manner in which Brodmann extended retrosplenial areas 29 and 30 onto the gyral surface where area 23 is located. RSC comprises the ventral bank of the cingulate gyrus in the callosal sulcus and is not exposed as suggested in his map. Abbreviations: cgs, cingulate sulcus; IG, indusium griseum; mr, marginal ramus of the cgs; pos, parieto-occipital sulcus; sCC, splenium of the corpus callosum; Sub, dorsal subiculum; VCA, vertical plane at the anterior commissure;

Figure 2

Figure 2

Morphological context of metabolic activity in PCC in monkeys. A. 2-deoxy-D-glucose utilization coded for four levels of utilization and thalamic projections to RSC shown with a tritiated-amino acid injection (hatched) into the anterior thalamic nuclei and a coronal section through RSC areas 29 and 30. The close relationship between high glucose metabolism and thalamic afferents are obvious. Interestingly, high levels of the mitochondrial enzyme cytochrome c oxidase also occur in the granular layer of RSC and in layers III-IV of areas 30 and 23. The asterisk in B shows where the section through ACC in C. was taken. Notice that ACC has much less cytochrome c oxidase activity than does area 23 (shown with the pair of arrows delineating these areas). A midcingulotomy lesion (D.; at coronal level shown with “v” on medial surface in B.) that removes thalamic afferents to PCC/RSC as well as frontal lobe inputs shows a massive reduction of activity in the thalamoreceptive layers as predicted from selective thalamic lesions in rat. There is about a 20% volumetric reduction in the posterior cingulate gyrus and reductions in enzyme activity are emphasized with three arrows from layer III/IV in area 29 and layers III and IV in areas 30 and 23c. Thus, high metabolic activity in PCC, RSC, and PrCC is driven primarily by thalamic afferents.

Figure 3

Figure 3

Estimates of rCBF in precuneal and posterior cingulate cortices during wakefulness and three stages of sleep. The pattern is similar for both cortices with a high level of rCBF during wakefulness and reductions during sleep. The one main difference between these areas is that PCC during stage II sleep has a higher level of activity than during REM than is the case for PrCC. Thus, the transition to sleep involves greater reductions in rCBF in PrCC than in PrCC.

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