Effect of prior cognitive state on resting state networks measured with functional connectivity

Abstract

To address the extent to which functional connectivity measures an absolute brain state, we observed the effect of prior performance of a language task on resting-state networks in regions associated with language. Six subjects were imaged during rest before and after a block-design language task. Connectivity maps were generated for each of four language regions (identified from analysis of the language activation portion of the study) in each subject for both rest periods. Conjunction analysis demonstrated distinct networks of voxels for each seed region, indicating separate functional subnetworks associated with the different regions. In a comparison of rest before and after the activation task widespread and significant changes were observed in all individuals, suggesting that the measured resting state network reflects a dynamic image of the current brain state. At the group level, an extended network was observed that was largely persistent over time. Even at the group level an increase in connectivity was observed between left and right middle frontal gyri, and between posterior cingulate cortex and medial frontal cortex in the rest after the language task. These results suggest that functional connectivity may be a powerful measure of cognitive state, sensitive to differences between controls and patients together with the particular cognitive processing occurring during the rest state.

Figure 1

Brain activity during the OLR task. Main effect of OLR task above (activation) and below (deactivation) the baseline fixation condition. A: Results projected onto the surface of a single rendered brain (activation, red; deactivation, green). B: Results are overlaid onto the average EPI of the six subjects, with activation (task > rest) shown in “hot” colours and deactivation in “cold” colours.

Figure 2

Seeded functional connectivity maps of Subject A, showing regions correlated with ACC, PCC, left IFG, and left MFG ROI average signal time‐courses shown in red, blue, green, and yellow, respectively. A: Initial rest period. B: Rest period immediately after an OLR vs. baseline paradigm. C: Comparison of the two rest periods, REST1 > REST2. D: REST2 > REST1. Legend shows the colour scale, with intermediate colours (between two regions) representing the overlap of those two maps.

Figure 3

Seeded functional connectivity maps of Subject B, showing regions correlated with ACC, PCC, left IFG, and left MFG ROI average signal time‐courses shown in red, blue, green, and yellow, respectively. A: Initial rest period. B: Rest period immediately after an OLR vs. baseline paradigm. C: Comparison of the two rest periods, REST1 > REST2. D: REST2 > REST1.

Figure 4

Seeded functional connectivity over the six subjects, showing regions correlated with ACC, PCC, left IFG, and left MFG ROI average signal time‐courses shown in red, blue, green, and yellow, respectively. A: Initial rest period. B: Rest period immediately after an OLR vs. baseline paradigm. C: Comparison of the two rest periods, REST1 > REST2. D: REST2 > REST1. Significant increases in connectivity are seen for the PCC map (cluster in medial frontal cortex circled), and the left MFG map (cluster in the right MFG, indicated by a square)

Figure 5

Average percentage overlap between each of the FC maps in Figure 4, and how these overlaps vary between the two resting periods. From left to right: bars represent overlap between ACC and left IFG, ACC and left MFG, ACC and PCC, IFG and MFG, IFG and PCC, and MFG and PCC. A: Overlap before the language task. B: Overlap after the task period.