Functional connectivity and brain activation: a synergistic approach

Abstract

Traditional functional magnetic resonance imaging (fMRI) studies exploit endogenous brain activity for mapping brain activation during "periodic" cognitive/emotional challenges or brain functional connectivity during the "resting state". Previous studies demonstrated that these approaches provide a limited view of brain function which can be complemented by each other. We hypothesized that graph theory functional connectivity density (FCD) mapping would demonstrate regional FCD decreases between resting-state scan and a continuous "task-state" scan. Forty-five healthy volunteers underwent functional connectivity MRI during resting-state as well as a continuous visual attention task, and standard fMRI with a blocked version of the visual attention task. High-resolution data-driven FCD mapping was used to measure task-related connectivity changes without a priori hypotheses. Results demonstrate that task performance was associated with FCD decreases in brain regions weakly activated/deactivated by the task. Furthermore, a pronounced negative correlation between blood oxygen level-dependent-fMRI activation and task-related FCD decreases emerged across brain regions that also suggest the disconnection of task-irrelevant networks during task performance. The correlation between improved accuracy and stronger FCD decreases further suggests the disconnection of task-irrelevant networks during task performance. Functional connectivity can potentiate traditional fMRI studies and offer a more complete picture of brain function.

Keywords: FCD; attention; fMRI; hub; performance.

Published by Oxford University Press 2013. This work is written by (a) US Government employee(s) and is in the public domain in the US.

Figures

Figure 1.

Study design (A). After a standard “resting-state” functional connectivity (RSFC) scan, the 45 healthy subjects underwent a “task-state” functional connectivity (TSFC) scan were they tracked 2 of the 10 moving balls, continuously during 5 min, followed by a BOLD-fMRI of a blocked version of this visual attention task during 6 min. Time courses of the MRI signal (left) in the SPC and their Fourier spectra (right) during RSFC and TSFC (B) and BOLD fMRI (C) and the canonical HRF used to compute the brain activation (red-yellow: T-score window: 3–10) and deactivation (blue-cyan: T-score window: −3 to −10) patterns for each subject.

Figure 2.

Statistical t-score maps for brain activation (red-yellow) and deactivation (blue-cyan) during the ball-tracking task (top row) as well as for the task-related decreases in local (lFCD; middle row) and global (gFCD; bottom row) functional connectivity densities superimposed on the surface of the Colin human brain template. Independent within-subjects ANOVA for each image modality. Sample size: 45 healthy subjects.

Figure 3.

Regions that showed significant (P < 0.001, uncorrected) task-related connectivity decreases (red-yellow) for datasets with and without scrubbing, superimposed on axial views of the human brain.

Figure 4.

(A) Nonoverlapping patterns of BOLD-fMRI and task-related lFCD decreases and their overlap. (B) Scatter plot showing the negative correlation of brain activation and task-related lFCD decreases. The lFCD hubs were sorted by their strength into bins of ΔFCD = 1 and the average lFCD and BOLD fMRI values computed within these ΔFCD bins using IDL.

Figure 5.

Statistical significance of the decreases in the strength of the functional connectivity for seed regions that demonstrated lower FCD for the TSFC scans than for the RSFC scans (Tables 1 and 2; bold region labels).

Figure 6.

Statistical t-score maps for the negative correlations with performance accuracy during blocked (BOLD fMRI; left column) and continuous (lFCD and gFCD; middle and right columns, respectively) ball tracking, superimposed on the surface of the Colin human brain template, and scatter plots exemplifying these correlations for the main clusters listed in Table 3. Blue circles mark the approximated locations of the clusters on the brain surface. Red lines are linear regression plots of the data. Labels indicate brain regions and Pearson correlation factors (R). Independent simple regression analyses for each image modality. Sample size: 45 healthy subjects.