Poster #4 - Association between Hippocampal Functional Connectivity, Sleep, and Memory during Early Childhood.

• In Event: Poster Session 10

Abstract

Introduction: Sleep, memory, and hippocampal connectivity all undergo changes during early childhood (i.e., age 3 to 5 years). Specifically, there are important shifts in sleep habits (e.g., cessation of napping) and marked improvements in episodic memory performance (Riggins 2014). Past work has also shown that memory improvements from early to middle childhood are supported by increases in hippocampal connectivity with a network of six cortical ROIs (IOG, OFG, IPL/SPL, ITG, and IFG) that are independently related to memory (Geng et al., 2019).

These coinciding developmental changes may be partially explained by the active consolidation hypothesis that suggests memories are consolidated from the hippocampus to the cortex during sleep (Rasch & Born, 2013). Specifically, increases in hippocampal-cortical connectivity during early childhood may be related to increased efficiency of memory consolidation ability during sleep in this age group. However, previous studies have not examined relations between hippocampal connectivity, sleep, and memory consolidation associated with an afternoon nap. The purpose of this investigation is to explore these associations.

Methods: This investigation utilized a cross-section sample of 39, 3-to-5-year-old participants (M= 4.3 years, SD = 0.10) taken from a longitudinal study. To assess memory performance across a nap and wake session each subject completed a memory task by encoding image locations on a grid. They were then tested on the image locations before (test 1) and after (test 2) a nap and equivalent wake period (within-subject). Wake and sleep difference scores were calculated as follows (test 2 - test 1)/ test 2. Nap benefit score was calculated as sleep difference score - wake difference score.

To assess hippocampal connectivity, subjects participated in an MRI scan where a T1-weighted image and a 7-minute resting state fMRI scan were collected. Hippocampal seed regions were obtained via Freesurfer 6.0 and adjusted with ASAT. To address motion, volumes with a framewise displacement >0.05 were scrubbed. Time-series correlations between total hippocampus and six cortical ROIs drawn from a previous study (Geng et al., 2019) were calculated to measure hippocampal connectivity. The methods and analytic approach used in this investigation are pre-registered, but embargoed, on the OSF website.

Results & Conclusion: Multiple regression was used to assess associations between hippocampal connectivity and nap benefit score, controlling for several confounding variables (e.g., age and sex). Consistent with our hypothesis, there was a positive association between hippocampal connectivity with left Inferior Frontal Gyrus (IFG) and nap benefit score (β = 2.094, p = .01]). This finding suggests that children who have stronger connectivity between the hippocampus and IFG demonstrate greater nap-related memory consolidation.

In contrast, there was also a negative association between hippocampal connectivity with Inferior Occipital Gyrus (IOG) and nap benefit score (β = -2.25, p = .04), suggesting that children who have stronger connectivity between the hippocampus and IOG demonstrate less nap-related memory consolidation. Future analysis will explore additional factors related to these findings (e.g., variations in encoding and nap status) to gain better understanding of relations between hippocampal connectivity, sleep, and the memory benefit associated with an afternoon nap.

Authors

• Tamara Lynn Allard, University of Maryland - College Park
  Presenting Author

• Morgan Botdorf, University of Maryland - College Park

• Jade Dunstan, University of Maryland - College Park

• Sanna Lokhandwala, University of Massachusetts Amherst

• Rebecca Spencer, University of Massachusetts, Amherst

• Tracy Riggins, University of Maryland - College Park