Page 94 - Like me, or else... - Michelle Achterberg

Chapter 4
solved by realignment, we included six additional motion regressors (corresponding to the three translational and rotational directions) as covariates of no interest. The least squares parameter estimates of height of the best-fitting canonical HRF for each condition were used in pairwise contrasts. The pairwise comparisons resulted in subject-specific contrast images.
Higher-level group analyses
Subject-specific contrast images were used for the group analyses. A full factorial ANOVA with three levels (positive, negative and neutral judgment) was used to investigate the neural response to the social feedback event. To investigate regions that were activated during both negative and positive feedback, we conducted a conjunction analysis to explore the general valence effects of social evaluation (conjunction negative > neutral and positive > neutral). Based on Nichols et al. (2005), we used the ‘logical AND’ strategy. The ‘logical AND’ strategy requires that all the comparisons in the conjunction are individually significant (Nichols et al., 2005). Next, we calculated the contrasts negative > positive and positive > negative to investigate brain regions that were specifically activated for social rejection or social acceptance. All results were family wise error (FWE) voxel level corrected, with pFWE<.05. Coordinates for local maxima are reported in MNI space.
Region of Interest analyses
SPM8’s MarsBaR toolbox (Brett et al., 2002) was used to extract patterns of activation from the whole brain group analyses in order to investigate possible brain-behavior associations and as input for the genetic modeling. Parameter estimates (PE, average Beta values) were extracted from regions that were significantly activated in the whole brain analyses. Specifically, the following ten regions were extracted: the left and right insula and ACCg (from the conjunction contrast); the mPFC and left and right IFG (contrast negative>positive); and the left and right DLPFC, SMA, and caudate (contrast positive>negative). For the brain- behavior relations we focused on associations with noise-blast difference scores following negative social feedback (negative-positive and negative-neutral, corrected for age and IQ).
Genetic modeling
Zygosity was determined using DNA analyses. DNA was tested with buccal cell samples collected via a mouth swab (Whatman Sterile Omni Swab). Buccal samples were collected directly after the MRI session, thereby ensuring that the children did not have anything to eat or drink for at least one hour prior to DNA collection. The results of the DNA analyses indicated that 55% of the twin pairs was MZ.
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