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                                Chapter 6
 between sample I and II. Paired sample t-tests were used to test whether there were differences in connectivity between ROIs and the VS and AMY seeds.
Genetic Modeling
Within the final sample (N=220), there were 64 complete twin pairs (37 MZ and 27 DZ, Table 2). Zygosity was determined by 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 had not eaten for at least one hour prior to DNA collection.
Similarities among twin pairs can be due to shared genetic factors (A) and shared environmental factors (C), while dissimilarities are ascribed to unique environmental influences and measurement error (E), see Fig S2. Behavioral genetic modeling with the OpenMX package (Neale et al., 2016) in R (R Core Team, 2015) provides estimates of these A, C, and E components. Since several heritable psychiatric disorders are associated with limbic/subcortical-PFC connections (Bouchard and McGue, 2003; Flint and Kendler, 2014), VS and AMY connectivity might also be heritable. However, these regions have also shown plasticity to the environment (Tottenham and Galvan (2016), which could indicate influences of (shared or unique) environment. Therefore, we calculated the ACE models for each of the 17 seed-ROI connections and report the point estimates and 95% confidence intervals of A, C and E. High estimates of A indicate that genetics play an important role, whilst C estimates indicate influences of the shared environment. If the E estimate is the highest, variance in connectivity is mostly accounted for by unique environmental factors and measurement error. Comparisons of the ACE models with more parsimonious models (AE model, CE model, and E model) are described in the Supplementary Materials.
Results
First, we performed whole brain analyses for the subcortical seeds (VS and AMY) in sample I and II. Next we investigated the overlap between the two samples by using conjunction analyses.
Ventral Striatum
Whole brain functional connectivity with the VS as seed for sample I is displayed in Fig 2a (left top panel) and Table S3. Whole brain results for sample II are displayed in Fig 2a (right top panel) and Table S4. To formally assess which connectivity patterns replicated across samples, conjunction analyses were performed. As visualized in Fig 2a, whole brain VS connectivity in the two
Whole Brain Analyses
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