Functional network connectivity during rest and task conditions: a comparative study

Abstract

Functional connectivity (FC) examines temporal statistical dependencies among distant brain regions by means of seed-based analysis or independent component analysis (ICA). Spatial ICA also makes it possible to investigate FC at the network level, termed functional network connectivity (FNC). The dynamics of each network (ICA component), which may consist of several remote regions is described by the ICA time-course of that network; hence, FNC studies statistical dependencies among ICA time-courses. In this article, we compare comprehensively FNC in the resting state and during performance of an auditory oddball (AOD) task in 28 healthy subjects on relevant (nonartifactual) brain networks. The results show global FNC decrease during the performance of the task. In addition, we show that specific networks enlarge and/or demonstrate higher activity during the performance of the task. The results suggest that performing an active task like AOD may be facilitated by recruiting more neurons and higher activation of related networks rather than collaboration among different brain networks. We also evaluated the impact of temporal filtering on FNC analyses. Results showed that the results are not significantly affected by filtering.

Keywords: fMRI; functional network connectivity; independent component analysis.

Figure 1

Block diagram of the proposed approach. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 2

SMs of the 10 selected IC components. The time‐course of each component during AOD task was regressed against task paradigms (see section “Component Selection”). The P‐value for the regression coefficients corresponding to novel and target stimulations are color‐coded in the bottom left and right corners of each component, respectively. Reference color bar is shown on the right side of the figure.

Figure 3

Left column: mean of correlation pairs for rest and AOD. Right column: T‐value of each correlation pair resulted from Student t‐test. Top row: unfiltered components. Bottom row: filtered components. Black circles indicate the pairs surviving the t‐test with a FDR corrected P‐value threshold of 0.05.

Figure 4

Left: mean correlation difference between rest and AOD (rest‐AOD) for filtered and unfiltered components. Right: T‐value resulting from paired t‐test with FDR corrected P‐value threshold of 0.05 for filtered and unfiltered components. Stars: pairs surviving the paired t‐test.

Figure 5

Volume of each functional network during rest and task averaged over subjects. Each black error bar is symmetric and twice the standard error of the mean long. Red stars show components surviving paired t‐test at FDR corrected 0.05 level between the volumes in the two states.

Figure 6

Peak activation for each component during rest and task. A voxel‐wise one sample t‐test on each component (each subject is an observation) for each state was performed. Then the highest T‐value of the test is illustrated in this Figure. The highest activated voxel is not necessarily the same for rest and task.