Chapter 7 – Pharmacological fMRI 233 were realigned to correct for motion artifacts, low frequency drift, temporal autocorrelation, and spatial abnormalities. Structural scans were co-registered to the mean echo planar imaging space, and data was normalized and registered to Montreal Neurological Institute (MNI) space. A Gaussian spatial smoothing kernel of 6mm full width at half maximum was applied to the functional images. Data were visually inspected for successful co-registration. The four functional scans were preprocessed separately, then concatenated to one set of functional images per participant. Heart rate and respiratory data were preprocessed with the PhysIO toolbox 55. For statistical analysis, functional images were modeled on a design matrix consisting of columns for 1. Baseline moderate pain trials, 2. Baseline high pain trials, 3. Acquisition control trials, 4. Acquisition nocebo trials, 5. Evocation control trials, 6. Evocation nocebo trials, 7. Extinction control trials, 8. Extinction nocebo trials (columns 1-8 of the design matrix, each modeled with the onset and duration of the approximately 7000ms pain stimulus), 9. Pain rating periods, 10. Control and nocebo anticipatory cues, 11. RETROICOR regressors for heart rate, respiration, and heart rate-respiration interaction 56; 12. respiratory volume per time; 13. heart rate variability (HRV; 11-13 estimated with the PhysIO toolbox); and 14. six motion regressors for the rigid body transformation. All task regressors (1-10) were convolved with the hemodynamic response function. Data were additionally high-pass filtered with a cut-off of 128s and corrected for temporal autocorrelation with a first-order autoregressive model. First level analyses pertaining to our hypotheses contrasted acquisition control trials with acquisition nocebo trials, evocation control trials with evocation nocebo trials, and baseline high pain trials with evocation nocebo trials. The evocation phase consisted of the first 10 extinction trials and exploratory analyses of the extinction phase included the remaining 18 extinction trials. Second level analyses compared these
RkJQdWJsaXNoZXIy MTk4NDMw