To Nap or Not: Relations Between Napping, Brain Development, and Memory in Preschool Children

• In Event: 3-188 - Sleep, Memory and the Brain During Development

Integrative Statement

While it is uniformly agreed on that children in the U.S. fail to get enough sleep, the amount of sleep needed and the cost of insufficient sleep are unclear particularly in early childhood (Galland et al., 2012). This age is unique with respect to sleep as children transition from a biphasic (consisting of a nap and an overnight sleep bout) to a monophasic sleep pattern. However, there are significant individual differences in the timing of this transition. Research has suggested that this transition reflects brain maturation (Kurth et al., 2010; Lam et al., 2012) and has important consequences for learning and memory (Spencer, 2013). For example, it has been shown that episodic memories are consolidated over naps in preschool age children regardless of nap habituality. However, when children are prevented from napping, memory decay is greater for children who nap habitually compared to children who no longer nap (Kurdziel et al., 2013). We propose that this difference reflects variation in brain maturation of the groups: those who no longer nap have more developed memory networks compared to those who nap habitually.

To address this hypothesis, we compared measures of memory and brain development in 3 groups of preschool children: those who napped (1) habitually, (2) occasionally, or (3) rarely. Parents completed the Children’s Sleep Habits Questionnaire (Owens et al., 2000). Children performed a battery of cognitive tasks, including an ordered recall task that requires participants to reproduce the order of an arbitrarily ordered sequence of pictures (Bauer et al., 2013) and indices of visuospatial and verbal IQ (WPPSI, Wechsler, 2012). Children also underwent MRI scanning, which yielded measures of global brain development (i.e., total gray matter, total white matter) as well as measures of the hippocampus, a critical region for memory (i.e., hippocampal subfield volumes).

Preliminary data are available from 36 children (12 per nap-status group, mean age = 4.48 years). As summarized in Table 1, there were no differences between groups in age, sex, 24-hour sleep duration, IQ, or total gray or white matter volumes. However, there were marginal differences between the three groups in memory performance (p = .10) and significant differences in volumes of hippocampal subfields (ps<.05). Consistent with the hypothesis, memory was better in children who rarely napped, compared to children of the same age who were still napping either occasionally or habitually. Additionally, hippocampal subfield volumes varied as function of nap status, with the smallest volumes observed in children who rarely napped, consistent with previous studies showing a decrease in volume with age (Riggins et al., 2018).

This is the first study to directly examine links between napping, memory, and brain development in preschool children. Our results are consistent with the hypothesis that as the brain (specifically the hippocampus) matures and becomes more efficient, day-time sleep need may decrease and result in an increase in memory performance. This finding is not only important for understanding developmental improvements in memory but also individual differences in memory and sleep in children of the same age.

Authors

• Tracy Riggins, University of Maryland
  Presenting Author

• Rebecca M. C. Spencer, University of Massachusetts Amherst
  Non-Presenting Author