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Subcortical-PFC resting state connectivity
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The few studies that examined these contributions in monozygotic (MZ) and dizygotic (DZ) twins in adults reported significant influences of genetics on functional connectivity, with little shared environmental influences (for a review see Richmond et al. (2016)), although some studies reported influences of both genetics and shared environment (Yang et al., 2016). Prior findings are mostly based on adult twin studies, whereas limbic/subcortical-PFC connectivity changes considerably during child and adolescent development. That is to say, functional connectivity from the ventral striatum and the amygdala with (medial) prefrontal regions increases substantially during development (Gabard-Durnam et al., 2014; Fareri et al., 2015; van Duijvenvoorde et al., 2016a). This increase in long range interactions between the ventral striatum, the amygdala, and the PFC may contribute to the improved ability of children to regulate behavior and emotions in the transition to adolescence (Somerville et al., 2010; Ernst, 2014; Casey, 2015). Together, these findings underscore the importance of studying heritability of RS brain connectivity in childhood.
Taken together, the aims of the current study were to investigate (1) the robustness of limbic/subcortical-cortical and limbic/subcortical-subcortical brain connectivity in childhood, and (2) the heritability of these connections in 7-to-9-year-old twins (N=220). We included 7- to-9-year-old twins since they are old enough to produce relatively good MRI data, while still representing (middle) childhood as a developmental phase. The study pursued two goals: 1) to investigate subcortical-cortical and subcortical-subcortical brain connectivity in childhood using two key limbic structures: the ventral striatum and the amygdala, and 2) to examine the heritability of these connections comparing MZ and DZ twins. We specifically focused on connectivity between limbic/subcortical regions and six PFC regions: the vmPFC, the vACC, the OFC, the dmPFC, the dACC and the dlPFC. These regions have been shown to be functionally connected to both the ventral striatum and the amygdala in adults (Di Martino et al., 2008; Roy et al., 2009) and display developmental changes related to increased cognitive control and emotion regulation (Somerville et al., 2010; Ernst, 2014; Casey, 2015), making them key targets to study in our sample.
The first question, regarding replicability of childhood RS connectivity, was addressed in two independent samples in order to examine connectivity patterns without genetic components. This allowed us to test for replication, thereby contributing to the debate about reproducibility of neuroscientific patterns (Open Science, 2015). Next, we specifically focused on RS-fMRI connectivity from the ventral striatum and amygdala to the six PFC regions and two additional subcortical regions (thalamus and hippocampus); since prior studies have shown that these regions show important developmental effects (Gabard-Durnam et al., 2014; Fareri et al., 2015). Based on prior studies, we expect to find replicable and robust resting state connectivity in childhood (Misic and Sporns, 2016), with distinctive patterns for ventral striatum and amygdala (Roy et al., 2009; Choi et al., 2012; Porter et al., 2015).
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