Task and task-free FMRI reproducibility comparison for motor network identification

Abstract

Test-retest reliability of individual functional magnetic resonance imaging (fMRI) results is of importance in clinical practice and longitudinal experiments. While several studies have investigated reliability of task-induced motor network activation, less is known about the reliability of the task-free motor network. Here, we investigate the reproducibility of task-free fMRI, and compare it to motor task activity. Sixteen healthy subjects participated in this study with a test-retest interval of seven weeks. The task-free motor network was assessed with a univariate, seed-voxel-based correlation analysis. Reproducibility was tested by means of intraclass correlation (ICC) values and ratio of overlap. Higher ICC values and a better overlap were found for task fMRI as compared to task-free fMRI. Furthermore, ratio of overlap improved for task fMRI at higher thresholds, while it decreased for task-free fMRI, suggesting a less focal spatial pattern of the motor network during resting state. However, for both techniques the most active voxels were located in the primary motor cortex. This indicates that, just like task fMRI, task-free fMRI can properly identify critical brain areas for motor task performance. Although both fMRI techniques are able to detect the motor network, resting-state fMRI is less reliable than task fMRI.

Keywords: intraclass correlation; overlap; primary motor cortex; reliability; resting-state fMRI; task fMRI; thresholding.

Figure 1

Motor task activation of Subjects 2 and 12 for scan Session 1 (in red) and scan Session 2 (in blue), rendered on subject's anatomy, in turn resliced in MNI space. Axial slices are shown in neurological orientation (left is left) with the corresponding coordinate on top of each slice. Z‐values for activated voxels exceeding the threshold (P < 0.05 corrected) ranged from 5.1 to 19.3 for scan Session 1, and from 5.1 to 18.7 for scan Session 2 for Subject 2. Z‐values ranged from 5.1 to 16.3 for scan Session 1, and from 5.1 to 20.5 for scan Session 2 for Subject 12. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 2

Task‐free functional connectivity of Subjects 2 and 12 for scan Sessions 1 (in red) and 2 (in blue), rendered on subject's anatomy, in turn resliced in MNI space. Axial slices are shown in neurological orientation (left is left) with the corresponding coordinate on top of each slice. Z‐values for activated voxels exceeding the threshold (P < 0.05 corrected) ranged from 5.1 to 29.8 for scan Session 1, and from 5.1 to 31.2 for scan Session 2 for Subject 2. Z‐values ranged from 5.1 to 29.4 for scan Session 1, and from 5.1 to 34.3 for scan Session 2 for Subject 12. The highest Z‐values are found near the seed region which is included in the figure. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 3

Individual whole brain ICC_within values for motor task (depicted by blue open squares) and task‐free (depicted by red open circles) fMRI. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 4

Between session averaged across all subjects overlap values for task (depicted by blue open squares) and task‐free (depicted by red open circles) fMRI for different thresholds based on Z‐values. The maximum Z‐value present in all subjects and sessions was 9 for task, and 11.5 for task‐free fMRI. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 5

Between session averaged across subjects overlap values for task (depicted by blue open squares) and task‐free (depicted by red open circles) fMRI for different supra‐threshold voxels (range 10–10,000 voxels). The x‐axis is scaled logarithmically. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 6

The 100 most active motor task voxels of Subjects 2 and 12 for scan Sessions 1 (in red) and 2 (in blue), rendered on subject's anatomy, in turn resliced in MNI space. Axial slices are shown in neurological orientation (left is left) with the corresponding coordinate on top of each slice. Corresponding Z‐values ranged from 10 to 19.3 for scan Session 1, and from 8.3 to 18.7 for scan Session 2 for Subject 2. Corresponding Z‐values ranged from 9.1 to 16.3 for scan Session 1, and from 11.9 to 20.5 for scan Session 2 for Subject 12. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]

Figure 7

The 100 most active task‐free functional connectivity voxels of Subjects 2 and 12 for scan Sessions 1 (in red) and 2 (in blue), rendered on subject's anatomy, in turn resliced in MNI space. Axial slices are shown in neurological orientation (left is left) with the corresponding coordinate on top of each slice. Corresponding Z‐values ranged from 23.2 to 29.8 for scan Session 1, and from 21.8 to 31.2 for scan Session 2 for Subject 2. Corresponding Z‐values ranged from 12 to 29.4 for scan Session 1, and from 21 to 34.3 for scan Session 2 for Subject 12. The highest Z‐values are found near the seed region which is included in the figure. [Color figure can be viewed in the online issue, which is available at http://wileyonlinelibrary.com.]