Abstract
As different areas within the PMC have different connectivity patterns with various cortical and subcortical regions, we hypothesized that distinct functional modules may be present within the PMC. Because the PMC appears to be the most active region during resting state, it has been postulated to play a fundamental role in the control of baseline brain functioning within the default mode network (DMN). Therefore one goal of this study was to explore which components of the PMC are specifically involved in the DMN. In a sample of seventeen healthy volunteers, we performed an unsupervised voxelwise ROI-based clustering based on resting state functional connectivity. Our results showed four clusters with different network connectivity. Each cluster showed positive and negative correlations with cortical regions involved in the DMN. Progressive shifts in PMC functional connectivity emerged from anterior to posterior and from dorsal to ventral ROIs. Ventral posterior portions of PMC were found to be part of a network implicated in the visuo-spatial guidance of movements, whereas dorsal anterior portions of PMC were interlinked with areas involved in attentional control. Ventral retrosplenial PMC selectively correlated with a network showing considerable overlap with the DMN, indicating that it makes essential contributions in self-referential processing, including autobiographical memory processing. Finally, ventral posterior PMC was shown to be functionally connected with a visual network.The paper represents the first attempt to provide a systematic, unsupervised, voxelwise clustering of the human posteromedial cortex (PMC), using resting-state functional connectivity data. Moreover, a ROI-based parcellation was used to confirm the results.
Highlights
The posteromedial cortex (PMC) is an architectonically discrete region comprising the retrosplenial areas (BA 29 and 30), the posterior cingulate areas (BA 23a,b,c), the mesial parietal area in the precuneus region (BA 7m), and BA 31, a transition area between BA 23c and BA 7m [1,2]
In the lowermost posterior part of BA 7 we found an area characterized by visual connectivity (VIS)
In summary, our study provides further support for the coexistence of functional unity and diversity within the PMC proposed by Parvizi et al [19]
Summary
The posteromedial cortex (PMC) is an architectonically discrete region comprising the retrosplenial areas (BA 29 and 30), the posterior cingulate areas (BA 23a,b,c), the mesial parietal area in the precuneus region (BA 7m), and BA 31, a transition area between BA 23c and BA 7m [1,2]. Over the last few years, the PMC has received an increasing amount of attention because it has been identified as the most active brain region during a baseline state where healthy subjects are asked to lay in the scanner and ‘rest’ (i.e. the resting state). The PMC and other brain regions, including the inferior parietal lobule (principally the angular gyrus), the superior frontal gyrus and the medial frontal gyrus, have been consistently found to be more active at rest than during non-self directed cognitive tasks. This observation has suggested the existence of a resting state in which the brain remains active in an organized manner, the so-called Default Mode Network (DMN). Two research groups [4,5] independently and in parallel proposed the analysis of connectivity in the resting human brain in term of two diametrically opposed brain networks, identified on the basis of both spontaneous correlations within each network and anticorrelations between networks; the authors have identified cortical foci for intrinsically defined anticorrelated networks, the task-positive network (TPN) and the task-negative network (TNN)
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