Task-evoked functional connectivity does not explain functional connectivity differences between rest and task conditions

Abstract

During complex tasks, patterns of functional connectivity differ from those in the resting state. However, what accounts for such differences remains unclear. Brain activity during a task reflects an unknown mixture of spontaneous and task-evoked activities. The difference in functional connectivity between a task state and the resting state may reflect not only task-evoked functional connectivity, but also changes in spontaneously emerging networks. Here, we characterized the differences in apparent functional connectivity between the resting state and when human subjects were watching a naturalistic movie. Such differences were marginally explained by the task-evoked functional connectivity involved in processing the movie content. Instead, they were mostly attributable to changes in spontaneous networks driven by ongoing activity during the task. The execution of the task reduced the correlations in ongoing activity among different cortical networks, especially between the visual and non-visual sensory or motor cortices. Our results suggest that task-evoked activity is not independent from spontaneous activity, and that engaging in a task may suppress spontaneous activity and its inter-regional correlation.

Keywords: natural vision; spontaneous activity; task evoked functional connectivity; task-rest interaction.

Figure 1

Seed‐based functional connectivity findings. Seed‐based functional connectivity using a seed in (a) PCu, (b) V1, (c) V5, and (d) M1. Each panel shows the result for within‐session FC during eyes‐closed resting‐state (left), within‐session FC during the movie task (left middle), the within‐session FC difference during the movie relative to rest (right middle), and the task‐evoked FC computed using inter‐subject correlations (right). Cluster‐level significance thresholds were set at a p < 0.05 corrected for multiple comparisons. The color bar indicates z‐values [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 2

Whole‐brain inter‐regional functional connectivity with two levels of granularity. Cross‐correlation matrices corresponding to the FC during the resting state (far left) and the movie task (left middle), the FC difference during the movie relative to rest (right middle), and the task‐evoked FC computed using the inter‐subject approach (far right). FC matrices were calculated using Fan et al. Brainnetome atlas 246‐region functional parcellation (A, top) and the Yeo et al. 17‐network parcellation (B, bottom). The color bar indicates the average z‐transformed cross correlation values; only significant correlations (q < 0.05) are displayed. Abbreviations for the Yeo parcellation: Vis1, Visual network 1; Vis2, Visual network 2; Som1, Somatomotor network 1; Som2, Somatomotor network 2; dAt1, Dorsal attention network 1; dAt2, Dorsal attention network 2; vAt1, Ventral attention network 1; FrP1, Frontoparietal network 1; Lim1, Limbic network 1; Lim2, Limbic network 2; DMN1, Default mode network 1; FrP2, Frontoparietal network 2; FrP3, Frontoparietal network 3; DMN2, Default mode network 2; DMN3, Default mode network 3; DMN4, Default mode network 4; DMN5, Default mode network 5. The Brainnetome atlas abbreviations are provided in Fan et al. (2016) [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 3

To what extent does task‐evoked FC explain the difference in FC between task and rest conditions? The task‐evoked FC was used as a regressor for the task‐rest FC difference, using the 246‐region Brainnetome atlas (a, top) and the Yeo et al. 17‐network atlas (b, bottom). The percent variance explained by the task‐evoked connectivity for the 17‐network atlas was 0.02% and 1.62% for the 246‐region atlas. The color bar indicates z‐transformed correlation coefficients [Color figure can be viewed at http://wileyonlinelibrary.com]