201 Attention Regulation in Narcolepsy Type 1 MR images (220 slices; TR 8.2 ms; TE 3.8 ms; inversion time 670.4 ms; FOV 240 × 240 × 220 mm; matrix size 240 × 240; flip angle 8°; 1 × 1 × 1 mm3 voxel size). MRI processing The fMRI images were pre-processed and analysed using FMRIB’s Software Library (FSL FEAT, version 5.1, Oxford, United Kingdom). In brief, the scans were motion corrected, brain extracted, normalized, filtered using a 100 s high-pass filter, smoothed with a 5 mm full-width at half maximum (FWHM) Gaussian kernel and coregistered to the corresponding skull-stripped T1 image. Main task effect The main task effect was assessed as the BOLD activity difference combining the blocks of the two difficulty levels over all four repetitions compared to the baseline blocks. Each combined task block lasted for 62.150 seconds and the baseline blocks and individual difficulty levels for 31.075 seconds. Three first-level contrast images were created for each participant: task > baseline; baseline > task; higher difficulty level > moderate difficulty level. All higher-level main task effect analyses results were masked inclusively for the (sub) cortical grey matter, brainstem, and cerebellum. As visual inspection of second-level comparisons on task effect showed similar activation patterns in both groups and no significant between-group differences were seen in the formal group comparisons, we pooled the corresponding contrasts for healthy controls and people with narcolepsy type 1 in one group to increase power of the main task effect. Time-on-task effect To assess changes in brain activation over the entire SART, we compared task activation in the moderate and higher difficulty level combined between repetition one and four (62.150 seconds each) using the preceding baseline blocks as reference (31.075 seconds). In the within-block time-on-task effect, each block was evenly divided in two halves (15.538 seconds each) to reflect the transition from attention initiation to stable attention. A three-level procedure was used to study the overall time-on-task effect. In the first-level analysis, two contrasts were created per participant: task repetition 1 > baseline repetition 1; task repetition 4 > baseline repetition 4. These contrasts were fed in second-level analyses using fixed effects to generate within-participant contrasts bidirectionally comparing activation between repetition 1 and 4. Second-level contrasts were used for third-level 7
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