Echoes of the brain within the posterior cingulate cortex

Abstract

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.

Figure 1.

High-level schematic of the functional connectivity analysis. First, a group temporal concatenation ICA is performed to find separable spatial components within the PCC (top). These are then back projected to find a subject-specific time course for each PCC component. These time courses are then simultaneously entered into a GLM voxelwise throughout the brain, resulting in a functional connectivity map for each component.

Figure 2.

a, The locations (left) and the resulting maps of functional connectivity (right) of six or the 10 data-derived regions of interest. The results of the connectivity analysis are thresholded at p < 0.05, corrected for multiple comparisons. b, The overlap between the regions of interest, demonstrating the highest overlap in dorsal PCC. Warm colors indicate higher overlap.

Figure 3.

Consistency of resulting networks with seven (left), 10 (middle), and 15 (right) components (different columns).

Figure 4.

The effect of a simple attentional task on functional connectivity within the PCC. a, Regions positively activated (warm colors) or deactivated (in cool colors) by a choice reaction time task compared with rest (p < 0.05, cluster corrected for multiple comparisons). The time courses in red and blue illustrate the task-positive and task-negative phases. Representative time courses are shown for task and fixation. b, A comparison of functional connectivity maps for four regions of interest during task (i.e., blocks of active task and fixation) and during a separate rest scan with no explicit task. The spatial correlation between the functional connectivity during the resting scan and during the task scan are as follows: ROI 1, r = 0.86; ROI 3, r = 0.77; ROI 4, r = 0.93; ROI 9, r = 0.55. c, Task-activation of regions of interest. Asterisks indicate regions that are significantly modulated (in this case, deactivated) on task.

Figure 5.

a, Effect of multivariate versus univariate analyses functional connectivity. Left, Similarity (Pearson correlation) between each ROI's average time course (no multiple regression) and all the other ROIs' time courses. Right, Similarity matrix for the same ROIs after multiple regression. Blue colors have a low correlation coefficient; red colors have a high correlation coefficient. b, Functional connectivity results during the rest scan, either using univariate or multivariate statistics. Results have been thresholded using family-wise error correction for multiple comparisons, p < 0.05. c, Comparing the effect of task with the multivariate approach and the univariate approach. An asterisk denotes a result which is significant at the p < 0.05 level and a false discovery rate corrected at q < 0.05.