Sentient from conception, Paul Atreides — the in utero protagonist of the classic novel Dune — awakens abruptly to a superhuman consciousness.
Yet most others in the earthly realm rise at a slower pace, making incremental leaps forward in sudden flashes of understanding, from birth well into adulthood, says Rebecca Gómez of the University of Arizona. Sometimes a slow and steady drip, learning typically comes to infants and young children with a sudden deluge, often following a short nap.
Now, a growing scientific consensus understands how the brain reactivates memories during sleep, with new research gleaning insight into how memories are stored and accessed, says Susanne Diekelmann, a researcher from the University of Tübingen in Germany, who also presented findings at the meeting.
"Sleep is a highly selective state that preferentially strengthens memories that are relevant for our future behavior," Diekelmann said in the statement. "Sleep can also abstract general rules from single experiences, which helps us to deal more efficiently with similar situations in the future."
Among findings from Gómez is the idea that sleep is essential for enabling the young human brain to recognize patterns that may be applied to other situations, a mental process called generalization. Once a child has learned the alphabet, he or she would then recognize those same patterns later, even with alphabet letters printed in different fonts or colors. Language comprehension too comes with the ability to generalize, as children recognize basic grammatical patterns in new lessons moving forward.
To do this, they need sleep. "Sleep is essential for extending learning to new examples," Gómez said. "Naps soon after learning appear to be particularly important for generalization of knowledge in infants and preschoolers."
In one experiment, Gómez tested the nascent ability of infants to recognize new vocabulary during a prolonged period of wakefulness or just shortly after a nap. To do so, she played an artificial “training language” for the babies — think Klingon — that would not be confused with the living languages heard by the infants every day. Later, the researchers gauged the baby learning by measuring the length of time infants spent turning their heads to listen to spoken language — and whether they directed their attention to grammatical patterns gained previously through ambient learning.
"Infants who nap soon after learning are able to generalize after sleep but not after a similar interval of normal waking time," Gómez said.
The researchers also looked into how naps affected a preschooler's ability to learn new words. "Infants who nap soon after learning are able to generalize after sleep but not after a similar interval of normal waking time," Gómez said. "Preschoolers with more mature memory structures do not appear to form generalizations during sleep — [but] naps appear to be necessary for retaining a generalization they form before a nap."
Children in preschool may benefit from sleep in ways different from infants, as research on nonhuman primates suggests substructures of the brain’s hippocampus — present already in infancy — develop further to help replay memories during sleep. That wiring of the brain typically occurs during the course of several years beginning at 16 to 20 months of age.
As children age, sleep remains crucial to the development of the nascent brain, but for different reasons. Among other possible functions for sleep, says Diekelmann, is the need to remember our plans — as most of us are born lacking true sentience, itself a relative concept.