Office of Undergraduate Research

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Relations between amygdala:hippocampus ratios and depressive symptoms in typically developing 4- to 8-year-old children
(2020) Coley, Katherine; Turcios, Miguel; Weinberg, Benjamin; Riggins, Tracy; Riggins, Tracy
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.
Relations Between Hippocampal Volume and Story Recall in Early Childhood
(2020) Karayianis, Katherine; Ewell, Arcadia; Allard, Tamara; Weinberg, Benjamin; Riggins, Tracy
Research in adults and children suggest the hippocampus plays an important role in verbal memory (Ezzati et al., 2015; Gold & Trauner, 2014). However, links between verbal memory and the hippocampus in younger children remain relatively under investigated. This relation is important to study during early childhood (i.e., before 6 years) for at least two reasons. First, memory changes rapidly during this time and second, research in children suggests that age- related differences exist between memory and hippocampal subregion volumes (e.g. Riggins et al., 2015; Allard, Canada, & Riggins, March 2019). The current study addresses a gap in the literature by investigating the potential relation between hippocampal subregion volumes and verbal memory in early childhood. A total of 200 children, aged 4-8 years old (mean age=6.21 years, SD=0.11), were enrolled in a larger study on hippocampal memory development. Of these, 177 provided usable behavioral and MRI data. To assess verbal memory performance in these children, the stories subtest of the Children's Memory Scale was administered (Cohen, 1997). In the task, participants heard two stories read aloud by a researcher and were then asked to recall those stories immediately after hearing them, again one hour later, and again one week later. For the current study, analyses focused on the hour-delay performance in order to assess long term memory without the additional prompting that happened before the week-delay performance. Performance on the task was determined by the number of remembered verbatim story units. The maximum number of stories units to be remembered was 57 for both stories heard. Approximately one week following the verbal memory task, a T1-weighted structural MRI scan (0.9 mm3) was obtained. Hippocampal volumes were estimated via Freesurfer v5.1 (Fischl, 2012) and refined using ASAT (Wang et al., 2011). Hippocampal volumes were then divided into subregions (head, body, tail) using standard anatomical landmarks (Weiss, Dewitt, Goff, Ditman, & Heckers, 2005; Watson et al., 1992). Initial analyses examining hippocampal volume and verbal memory performance was non- significant. However, when a median age split was conducted, preliminary findings assessing relations between recall and hippocampal volumes revealed that younger (4- 6.13 years), but not older children (6.14-9 years) showed a significant positive relation between number of story units recalled and volume of the left hippocampal body (r=0.244, n=79, p=0.028). These findings are consistent with previous research that suggests developmental differences exist in brain-behavior relations during early childhood. It also supports the notion that a mature hippocampus is not necessarily larger in size (Riggins et al., 2015). These results reinforce an emerging body of work that propose age-related differences in associations between memory and hippocampal subregion volumes during development. Specifically, these results are consistent with previous findings that showed age-related differences between hippocampal body and performance on a visual spatial memory task and source memory in younger but not older children (Allard, Canada, & Riggins, March 2019; Riggins et al., 2015).

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