Page 21 - Like me, or else... - Michelle Achterberg

General introduction
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Previous studies using behavioral data showed high reliability of trait aggression (Miles and Carey, 1997; Rhee and Waldman, 2002; Ferguson, 2010; Tuvblad and Baker, 2011; Porsch et al., 2016). However, the majority of these studies have relied on questionnaire data and very few have used experiments. Also, the number of studies that have investigated heritability of neural mechanisms is scarce. The few studies that investigated genetic and environmental influences on brain function in adults reported significant influences of genetics on functional connectivity, with little shared environmental influences (for an overview, see Richmond et al. (2016)). It is important to note that heritability estimates for brain anatomy and connectivity differ across development such that heritability estimates are stronger in adulthood than in childhood (Lenroot et al., 2009; van den Heuvel et al., 2013). Unraveling the extent to which brain development in childhood is influenced by genetics and environment can provide important insights in which neural mechanisms might be more sensitive to environmental influences (Euser et al., 2016). Specifically, using a behavioral genetic approach can provide insights in the etiology of aggression following social evaluation and might offer a starting point for interventions aimed to improve social emotion regulation.
Imaging the Childhood Brain
The majority of previous experimental neuroimaging studies in youth were aimed at adolescence. Some also included children younger than ten years of age, but the sample sizes were often very small. Why has there been so little emphasis on imaging pre-pubertal youth? One possible reason for this could be because scanning children can be very challenging: The MRI scanner is quite imposing and can induce anxiety in children (Tyc et al., 1995; Durston et al., 2009). Such scanner related distress makes it less likely for children to successfully finish an MRI scan, resulting in reduced scan quantity and quality in children compared to older samples (Poldrack et al., 2002; Satterthwaite et al., 2013). However, in order to investigate individual differences (i.e., why are some children more sensitive to social evaluation than others), large sample sizes are required. Not only do we need large sample sizes to investigate inter-individual (between-person) differences in social behavior, multiple waves of that same large sample are needed to capture intra-individual (within-person) differences across development (Telzer et al., 2018). That is to say, to truly capture development we need longitudinal studies. Although more and more studies are using longitudinal methods, these are still not the norm, despite the overall notion that longitudinal research is the golden standard to study changes across development (Pfeifer et al., 2018).
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