Abstract
Recent resting-state functional MRI (fMRI) studies have revealed that the global signal (GS) exhibits a nonuniform spatial distribution across the gray matter. Whether this topography is informative remains largely unknown. We therefore tested rest-task modulation of GS topography by analyzing static GS correlation and dynamic coactivation patterns in a large sample of an fMRI dataset (n = 837) from the Human Connectome Project. The GS topography in the resting state and in seven different tasks was first measured by correlating the GS with the local time series (GSCORR). In the resting state, high GSCORR was observed mainly in the primary sensory and motor regions, whereas low GSCORR was seen in the association brain areas. This pattern changed during the seven tasks, with mainly decreased GSCORR in sensorimotor cortex. Importantly, this rest-task modulation of GSCORR could be traced to transient coactivation patterns at the peak period of GS (GS-peak). By comparing the topography of GSCORR and respiration effects, we observed that the topography of respiration mimicked the topography of GS in the resting state, whereas both differed during the task states; because of such partial dissociation, we assume that GSCORR could not be equated with a respiration effect. Finally, rest-task modulation of GS topography could not be exclusively explained by other sources of physiological noise. Together, we here demonstrate the informative nature of GS topography by showing its rest-task modulation, the underlying dynamic coactivation patterns, and its partial dissociation from respiration effects during task states.
Highlights
One of the major confounds that limits the cognitive and clinical applications in functional MRI is the global signal (GS), which is defined as the spatial average of time-varying blood oxygen level–dependent (BOLD) signals [1,2]
Rest-task modulation of global signal topography identical GS topography during the resting states on the 2 days (ICC = 0.9986, 95% CI 0.9985– 0.9988) (Fig 1C), suggesting a high reliability of GS topography across time
The spatial correlation between the ΔGSCORR and CAP1 showed significant positive correlations (r = 0.33 on average, p < 0.001), and the CAP4, as its opposite, showed significant negative correlation (r = −0.36 on average, p < 0.001), whereas the ΔGSCORR and CAP2 showed significant negative correlations (r = −0.66 on average, p < 0.001) and its opposite (CAP5) showed significant positive correlations (r = 0.67 on average, p < 0.001). These findings suggested that the GS topography is constituted by a combination of several coactivation pattern (CAP) that were modulated in the frequency of their occurrence during the tasks
Summary
One of the major confounds that limits the cognitive and clinical applications in functional MRI (fMRI) is the global signal (GS), which is defined as the spatial average of time-varying blood oxygen level–dependent (BOLD) signals [1,2]. The GS is often considered to represent.
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