by Dr Caroline Hendry (PhD Developmental Biology)
Many studies have shown that sleep is important for learning and memory in adults1 - 5. During sleep, new experiences acquired during the day are integrated into our memory, providing valuable new knowledge to help us to navigate our ever-changing lives. But is the same true for babies? Could taking a nap enhance your baby’s memory, even helping them to learn?
The answer is yes, according to a convincing study published by Friedrich and colleagues earlier this year in the highly-regarded journal Nature Communications6. In their paper the researchers showed that babies (9 – 16 months) who took a short nap (less than 1.5 hours) could remember the names of objects better than babies who did not nap. Furthermore, when the babies who napped were shown objects similar to those they had just learnt, they were able to transfer the learned name to the new, similar object, which the non-napping babies could not do.
Why is this important?
Remembering the names of objects is critical for language and communication. But the second finding is even more interesting: the babies who napped could group similar but not identical objects into the same general category. This process is called generalisation, and it cuts down on the amount of new information the brain must process in order to make sense of the world. It’s like you looking at a type of shark you have never seen before but still knowing that it is indeed a shark. Your brain recognises familiar items like the overall shape, the fins, the teeth and so on and puts it into the “shark” category that it has learnt from previous experience. This is a critical process in brain development and means that humans do not have to learn everything from scratch – very important for avoiding new types of sharks!
Baby brain: what’s going on during nap time?
Sleep is not a static process. While the body rests, the brain is busy processing everything that it experienced during waking hours. And it does this in a very particular way: certain stages of sleep are associated with different processing activities in different brain regions. In this study, the researchers found that the ability of the babies to group similar objects into categories was associated with a particular type of sleep brainwave called the “sleep spindle” brainwave. This is the same type of brainwave that has been found to associate with memory consolidation in adults7, 8, so it makes sense that it’s happening in babies’ brains too.
What about napping at other ages?
This study looked only at babies aged between 9 and 16 months, and not outside this age range. There have, however, been other studies on the effect of naps on memory and learning in infants, and the results are interesting. While everybody seems to agree that naps promote word generalisation in babies aged up to about 16 months6, 9, 10, it is not yet clear whether this holds true as children grow older. A study looking at naps in toddlers aged 2.5 years found that being awake as opposed to napping was critical for word generalisation11. However, a different study in preschool age children showed that midday naps did indeed enhance learning, although the learning here was to do with spatial memory, not word generalisation12. Importantly, in this last study the researchers identified sleep spindle brainwaves as the critical component in the midday naps, consistent with other studies looking at sleep and memory.
To further muddy the waters, a recent and widely publicised research article reported that napping is associated with later onset and poorer quality of sleep in children over the age of two13. Surprisingly however, there was no negative association found between napping and the cognitive ability (learning, memory), behaviour or health of the children, which one might expect if the children had sleep problems. It is also not clear whether the napping was short, routine napping, or whether it was falling-asleep-in-the-car, unscheduled napping. Since the researchers did not actually conduct any experiments but rather compiled data from a number of existing studies, most of which were based on parent-based reporting rather than controlled experiments, this study should be interpreted with caution.
So what’s the bottom line?
Sleep is good! But you already knew that right? There is a wealth of research that supports the role of sleep in learning and memory processing, not to mention the importance of sleep for rest and repair of our other organs as well. But most of that data relates to overnight sleeping, and understanding why we nap and whether it’s good for us and our children is relatively unchartered territory. It is clear that baby naps are fundamental for cognitive development. A short, routine nap promotes memory formation and the creation of new knowledge. But the results are less clear when it comes to toddlers: most experimental data discussed here still argue that naps are important for memory and learning, but there are a few studies that claim the opposite. Why it would be important for babies and adults, but detrimental for toddlers, is a mystery. One thing is clear though: babies benefit from short naps, showing improved memory and learning compared to non-nappers. So dim the lights, turn on the white noise and get set for some serious napping!
1. Diekelmann et al. 2010. The memory function of sleep. J. Nat. Rev. Neurosci. 11, 114–126.
2. Djonlagic et al. 2013. Sleep enhances category learning. Learn. Mem. 16, 751–755.
3. Fenn et al. 2003. Consolidation during sleep of perceptual learning of spoken language. Nature 425, 614–616.
4. Ellenbogen et al. 2007. Human relational memory requires time and sleep. Proc. Natl Acad. Sci. USA 104, 7723–7728.
5. Wagner et al. 2004. Sleep inspires insight. Nature 427, 352–355.
6. Friedrich et al. 2015. Generalization of word meanings during infant sleep. Nat Commun. Jan 29;6:6004.
7. Gais et al. 2002. Learning-dependent increases in sleep spindle density. J. Neurosci. 22, 6830–6834.
8. Schabus et al. 2008 Interindividual sleep spindle differences and their relation to learning-related enhancements. Brain Res. 1191, 127–135.
9. Gomez et al. 2006. Naps promote abstraction in language- learning infants. Psychol. Sci. 17, 670–674.
10. Hupbach et al. 2009. Nap-dependent learning in infants. Dev. Sci. 12, 1007–1012.
11. Werchan et al. 2014. Wakefulness (not sleep) promotes generalization of word learning in 2.5-year-old children. Child Dev. 85(2):429-36.
12. Kurdziel et al. 2013. Sleep spindles in midday naps enhance learning in preschool children. Proc Natl Acad Sci U S A. 110(43):17267-72
13. Thorpe et al. 2015. Napping, development and health from 0 to 5 years: a systematic review. Archives of Disease in Childhood (Epub ahead of print)
Say! You might also be interested in reading one of these equally enthralling articles:
If you would like personalised help with any sleep issue for a child, newborn to 5 years, contact The Baby Sleep Company today on 0457 473 725 or click here to send us an email.