Resting-state fMRI Acquisition Protocol

Resting-state echo-planar images were acquired on an MR750 3T MR system (GE Healthcare) with a Nova Medical 32-channel head coil and were optimized for the detection of ventral frontal signal (222 volumes; 41 slices; descending sequential acquisition; repetition time = 2000 ms; echo time = 20 ms; matrix = 64 × 64; field-of-view = 211 mm; flip angle = 75°; slice thickness = 2.9 mm, slice gap = 0.1 mm, interslice distance = 3 mm). Shimming was automatically applied as part of the scanner’s prescan procedures, and 4 additional volumes were acquired and automatically discarded at the start of each fMRI run, allowing for T1 equilibration effects. As demonstrated by measurements of the temporal signal-to-noise, i.e., "the mean of a voxel’s blood-oxygen level–dependent signal over time divided by its standard deviation over time" (54 ), we obtained good coverage (Figure S1, Table S2).
Participants were shown a fixation cross on the screen and were instructed to keep their eyes open and let their mind wander while focusing on the cross. This setup has been shown to have higher reliability than other eyes-open or eyes-closed instructions (55 (link)). Respiration rate and heart rate were monitored. The total scan time was 7 minutes and 24 seconds. For more details on image acquisition, see the Supplemental Methods.