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Chapter 6
Discussion
We investigated genetic and environmental influences on limbic/subcortical- cortical and limbic/subcortical-subcortical RS-fMRI in a relatively large sample of 7-to-9-year-old MZ and DZ twins. As a complement to prior studies of genetic and environmental influences in adults (for example, Yang et al. (2016)), here we assessed twin concordance in children during a time of rapid development of these connections.
Replicability of childhood resting state connectivity
First we addressed childhood resting state brain connectivity, by studying patterns of connectivity from the ventral striatum and the amygdala, in two genetically independent samples. Reassuringly, and consistent with adult research (Power et al., 2010; Thomason et al., 2011; Misic and Sporns, 2016), we observed strongly replicable brain connectivity patterns over two samples of 7- to-9-year-old children, both in the whole brain seed based analyses and in the post-hoc ROI analyses. The general patterns showed positive connectivity between amygdala and ventral striatum and orbitofrontal cortex; and negative connectivity between these limbic/subcortical regions and dorsal medial and lateral regions. Previous studies showed that orbitofrontal cortex is more strongly involved in affective processes, whereas dorsal medial and lateral prefrontal cortex is more strongly associated with behavioral control, and the current findings fit with the hypothesized top-down control of dorsal lateral prefrontal cortex over the limbic subcortical brain regions (Somerville et al., 2010; Ernst, 2014; Casey, 2015).
In line with adult striatal-cortico connectivity patterns we found positive connectivity between the ventral striatum and vACC, vmPFC, and OFC (Di Martino et al., 2008), suggesting that these connections are already in place during middle childhood. The post-hoc ROI analyses indicated negative connectivity between the VS and the dACC, dlPFC and dmPFC, but these were less pronounced in the whole brain analyses. The difference between the current results and the connectivity patterns in adults could be due to developmental processes, since dorsal medial and lateral PFC regions continue to develop throughout adolescence (Ernst, 2014; Casey, 2015). Moreover, these differences in results might derive from the differences in limbic/subcortical seed regions. To date there is no consensus about the different sub regions of the striatum and different studies have used different approaches. Prior studies have suggested a more detailed subdivision of the striatum with, for example, additional distinctions within the ventral striatum (Di Martino et al., 2008; Choi et al., 2012). For the current paper we specifically chose only the ventral striatum, since this striatal sub region is specifically associated with developmental differences in affective/motivational behaviors. Future research could shed light on
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