Relations between amygdala:hippocampus ratios and depressive symptoms in typically developing 4- to 8-year-old children
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Previous literature suggests that the coordination between the amygdala and hippocampus, regions critical for encoding of complex memory and emotion, are associated with depression and risk factors for depression, such as negative memory bias, during adulthood (Yavas et al., 2019; Gerritsen et al., 2012). Research on adolescents ages 8-17 suggests that increased amygdala:hippocampus ratios are related to the severity of anxiety in pediatric major depression (MacMillan et al., 2003). Although associations between amygdala:hippocampus ratios and depression are well-documented in older samples, these associations are not well-explored in early childhood (i.e., <8 years). Given this is a developmental period during which both the amygdala and the hippocampus undergo structural and functional changes (Riggins et al., 2018; Stern et al., 2019), it may be especially important to understand how these developmental changes relate to depressive symptoms in early childhood. The present research aims to address this gap in the literature. Specifically, we examined depressive symptoms and amygdala:hippocampus ratios in typically developing 4- to 8-year-old children drawn from a larger, longitudinal study on brain development in early childhood (N=200, 100 female; Riggins et al., 2018). Depression scores were assessed using the Children’s Depression Inventory (CDI; Kovacs, 1985). Brain region volumes were collected using a standard resolution (.9mm3), T1-weighted whole brain structural magnetic resonance imaging (MRI) scan and processed using FreeSurfer (v5.1). In addition to amygdala and hippocampal volumes, intracranial volume (ICV) was collected as a control for participant head size. Analysis using partial correlations revealed a significant association between total amygdala:hippocampus ratios and depressive symptoms, r(50) = -.234, p = .048. The association between right amygdala:hippocampus ratios and depressive symptoms approached significance, r(50) = -.218, p = .060, and the association between left amygdala:hippocampus ratios and depressive symptoms were not significant. Contrary to previous research, smaller amygdala:hippocampus ratios predicted increased depressive symptoms. Implications for this research are discussed further.