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Subcortical-PFC resting state connectivity
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developmental differences in connectivity from different sub regions within the striatum, by directly comparing children and adults, using the same methodology in both samples (as was previously done for the VS by Fareri et al. (2015)).
Regarding amygdala-cortico connectivity, our developmental results were generally in line with the findings in adults. That is, we found positive connectivity with the OFC, the insula and the IFG, and negative connectivity with the dlPFC, dACC, dmPFC and parietal cortex (Stein et al., 2007; Roy et al., 2009). This is also in line with previous findings spanning ages from childhood to adulthood, showing that amygdala connectivity over development was largely stable (Gabard-Durnam et al., 2014). We did, however, find differences in amygdala-cerebellum connectivity compared to results in adults (Roy et al., 2009). Our whole brain analyses revealed a band of positive connectivity from the amygdala through the brainstem to the dorsal cerebellum, whereas adult results showed negative connectivity between the amygdala and the dorsal cerebellum (Roy et al., 2009). Interestingly, a recent study on amygdala functional connectivity in 4-to-7-year-old children also showed positive connectivity between amygdala and the cerebellum (Park et al., in press). We submit that this is a developmental effect, reflecting positive connectivity to the dorsal cerebellum in childhood that becomes negative over development. Indeed age dependent changes in amygdala connectivity have been documented, with increasingly negative connectivity between the amygdala and cerebellum with increasing age (Gabard-Durnam et al., 2014). Notably, a recent cross-sectional longitudinal study of Jalbrzikowski et al. (2017) reported strong amygdala-mPFC connectivity in childhood, which declined to zero by adulthood (age range 10- 19). However, we did not find strong amygdala-vmPFC connectivity in neither of the samples. This could be due to differences in age ranges, differences in the amygdala and vmPFC sub regions that were examined, as well as methodological differences in RS-fMRI analyses. In the current paper, we chose to use the whole amygdala as seed, to strike a balance between completeness and the number of connections and additional genetic analyses. However, it should be noted that the amygdala is not a single unit, but consists of several nuclei (Ball et al., 2007; Roy et al., 2009). Some studies have shown distinct connectivity patterns from different amygdala sub nuclei in adults (Roy et al., 2009), and over development (Gabard-Durnam et al., 2014).
In sum, our results showed robust and replicable whole brain connectivity in children, for the amygdala as well as the ventral striatum. In addition to previous studies that have shown that limbic/subcortical-cortical connectivity increases during adolescence (Fair et al., 2009; Vogel et al., 2010; Menon, 2013; Rubia, 2013; Gabard-Durnam et al., 2014); the findings from this study show that the vast architecture of this connectivity is already present before adolescence.
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