The Structure and Memory Benefits of Infant and Toddler Napping During the Triphasic-to-Biphasic Transition

• In Event: Enhance cognitive functions across development: factors, strategies or interventions

Abstract

Throughout infancy and toddlerhood, daytime napping aids memory (Seehagen et al., 2015; Friedrich et al., 2020). Though previous studies have assessed the general benefits of a nap on early memory, infants prior to 15 months are polyphasic, engaging in multiple morning and afternoon naps along with overnight sleep (Galland et al., 2012). No prior work has investigated whether infants’ morning and afternoon naps differ regarding their structure (physiology) and influence on memory, nor how each nap may support the other in learning across the day.

In the current study, we examine the relative benefits of infants’ morning and afternoon naps for declarative memory starting at 9 months, an age during which triphasic sleep (1 morning + 1 afternoon nap along with overnight sleep) is typical. To capture how the sleep architecture and benefits of morning and afternoon napping change as infants transition into a biphasic sleep pattern (1 midday nap + overnight sleep), we also track infants longitudinally, assessing nap effects on memory at 12 and 15 months. At each longitudinal timepoint, infants participate in two study conditions (order counterbalanced, 1-2 weeks apart). In the Nap condition, infants nap both in the morning and afternoon, with nap architecture recorded using 32-channel polysomnography (or actigraphy during social distancing). In the Wake condition, infants are kept awake during their morning nap, but are permitted to nap in the afternoon. Prior to the nap/wake intervals, infants participate in a deferred imitation task in which an experimenter models actions with novel objects. Infants’ memory for the actions is measured shortly following encoding, and again after each nap or wake period.

At 9 months (Fig. 1), behavioral analyses of our current sample (n=15, 5 female) indicate that when infants took both their morning and afternoon naps as normal, both naps protected new memories from significant decay (both ps>.28, Figs. 1a-b), with no differences in the degree of protection provided (change in memory, AMNapDay vs. PMNapDay: t(14)=.312, p=.759). In contrast, when infants skipped their morning nap, memories encoded in the morning tended to decay across the wake interval (t(14)=2.101, p=.054; Fig. 1c). Additionally, infants showed significant memory decay following their afternoon nap in the Wake condition (t(13)=2.349, p=.035; Fig. 1d), implying that morning wake disrupted the afternoon nap’s ability to protect memories. Despite this change in the afternoon nap’s memory benefits, preliminary nap physiology data (n=10) suggest no conditional differences in afternoon nap architecture (Fig. 2b). Finally, follow-up analyses at 12 and 15 months tentatively suggest a change in the effect of wake on memory, with infants showing improved memory in the morning after skipping their morning nap (12 months: t(6)=-2.465, p=.049; 15 months: t(5)=-2.712, p=.042) and retention of memories after all naps (ps>.203).

Our findings suggest that polyphasic sleep may be essential for protecting new memories at 9 months, but that the necessity of morning naps for memory retention may lessen with age. Further analyses will elucidate how individual differences in infants’ nap physiology may predict memory benefits across age.

Authors

• Gina Marie Mason, University of Massachusetts Amherst
  Presenting Author

• Laura Kurdziel, University of Massachusetts Amherst
  Non-Presenting Author

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