Page 34 - Like me, or else... - Michelle Achterberg

Chapter 2
As soon as the participant started the button press, the volume bar started to fill up with a newly colored block appearing every 350 ms. After releasing the button, or at maximum intensity (after 3500 ms), the volume bar stopped increasing and stayed on the screen for the remainder of the 5000 ms. Before the start of the next trial, another jittered fixation cross was presented (0 -11550 ms) (Figure 1). The length of the noise blast duration (i.e., length of button press) was used as a measure of aggression.
MRI data acquisition
MRI scans were acquired with a standard whole-head coil on a Philips 3.0 Tesla scanner. The data of the pilot sample were collected on a Philips Achieva TX MR system, the data of the test and replication sample were collected on a Philips Ingenia MR system. To prevent head motion, foam inserts surrounded the children’s heads. The SNAT was projected on a screen that was viewed through a mirror on the head coil. Functional scans were collected during three runs T2*- weighted echo planar images (EPI). The first two volumes were discarded to allow for equilibration of T1 saturation effect. Volumes covered the whole brain with a field of view (FOV) = 220 (ap) x 220 (rl) x 111.65 (fh) mm; repetition time (TR) of 2.2 seconds; echo time (TE) = 30 ms; flip angle (FA) = 80°; sequential acquisition, 37 slices; and voxel size = 2.75 x 2.75 x 2.75 mm. In the pilot sample the FOV was 220 (ap) x 220 (rl) x 114.68 (fh) mm, with a sequential acquisition of 38 slices. All other parameters were equal. Subsequently, a high-resolution 3D T1scan was obtained as anatomical reference (FOV= 224 (ap) x 177 (rl) x 168 (fh); TR = 9.72 ms; TE = 4.95 ms; FA = 8°; 140 slices; voxel size 0.875 x 0.875 x 0.875 mm). In the pilot sample the TR = 9.79 and the TE = 4.60, all other parameters were equal.
MRI data analyses
Preprocessing
MRI data were analyzed with SPM8 (Wellcome Trust Centre for Neuroimaging, London). Images were corrected for slice timing acquisition and rigid body motion. Functional scans were spatially normalized to T1 templates. Volumes of all children were resampled to 3x3x3 mm voxels. Data were spatially smoothed with a 6 mm full width at half maximum (FWHM) isotropic Gaussian kernel. SPM8’s ARTrepair toolbox (Mazaika et al., 2009) was used to detect and fix bad slices in preprocessed functional data. Slices with >1 mm scan to scan motion were detected and repaired. Children with >20% repaired slices were excluded from further analyses.
First-level analyses
Statistical analyses were performed on individual subjects’ data using a general linear model. The fMRI time series were modeled as a series of two events
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