April 9, 2014
Napping Helps Children Retain Memory, Learn New Skills
April Flowers for redOrbit.com - Your Universe Online
It seems like babies and young children are constantly learning new things and making giant developmental leaps. As if overnight, sometimes, they figure out how to recognize certain shapes or what the word "no" means no matter who says it.
A new study from the University of Arizona and the University of Tübingen shows that, in reality, making those leaps could be just a nap away. The findings, presented at the Cognitive Neuroscience Society (CNS) annual meeting this week, demonstrate that infants who nap are better able to apply lessons to new skills, and preschoolers who nap are better able to retain learned knowledge.
"Sleep plays a crucial role in learning from early in development," says Rebecca Gómez of the University of Arizona, whose work looks specifically at how sleep enables babies and young children to learn language over time.
"We want to show that sleep is not just a necessary evil for the organism to stay functional," says Susanne Diekelmann, of the University of Tübingen in Germany, who is chairing the symposium on sleep and memory. "Sleep is an active state that is essential for the formation of lasting memories."
[ Watch the Video: Good Sleep Equals Good Memory ]
According to a growing body of evidence, memories become reactivated during sleep. New research is illuminating exactly when and how memories are stored and reactivated. "Sleep is a highly selective state that preferentially strengthens memories that are relevant for our future behavior," Diekelmann says. "Sleep can also abstract general rules from single experiences, which helps us to deal more efficiently with similar situations in the future."
One of the developmental steps for young children is called generalization, or the ability to recognize similar, but not identical, instances to something they have already learned and apply it to the new situation. For example, the ability to recognize the letter "A" in different fonts, or understanding a word regardless of who is speaking it.
"Sleep is essential for extending learning to new examples," Gómez says. "Naps soon after learning appear to be particularly important for generalization of knowledge in infants and preschoolers."
To test the relationship between sleep and learning for infants, Gómez played a "training language" over loudspeakers to infants 12 months old who were playing. The babies were tested to find out if they recognized novel vocabulary in the artificial language after they had taken a nap, or been kept awake.
Gómez and her team found that infants who napped after hearing the new language were able to take the language rules learned before their nap and apply them, recognizing entirely new sentences in the language. To test the infants' recognition of the linguistic rules, the team measured the length of time infants spent with their heads turned to listen correctly versus incorrectly structured sentences in the language.
In creating artificial languages for her studies, Gómez mimics structure in natural language that may be useful in language learning. In many languages, for instance, nouns and verbs have subtly different sound patterns.
"If I want to study whether these patterns help infants learn language at a particular age, I build stimuli with similar characteristics into an artificial language," she says. "I can then test children of different ages to see when they are able to use this information."
The role of napping for preschoolers who were learning words was also examined.
"Infants who nap soon after learning are able to generalize after sleep but not after a similar interval of normal waking time," Gómez says. "Preschoolers with more mature memory structures do not appear to form generalizations during sleep; however, naps appear to be necessary for retaining a generalization they form before a nap."
The team suggests that the difference in learning and memory in infants versus preschool children could be the result of different neural mechanisms. Non-human primate research has revealed that although most substructures of the hippocampus are in place in infancy, the substructures that support the replay of memories during sleep do not begin forming until 16-20 months of age. These substructures take several more years to reach maturity.
"Therefore, we hypothesize that the benefits of sleep in infancy stem from different processes than those benefiting preschoolers," she says.
For infants, sleep might help to reduce the less redundant information – for example, the speaker's voice, the actual words infants hear over and above the rhythmic pattern occurring for all stimuli. For preschool children, however, Gómez says that hippocampally-based replay may begin to contribute to more active integration and retention of sleep-dependent memories.
ADULTS AND SLEEP
It seems that sleep not only helps us to remember our past, but also to remember the things we want to accomplish in the future.
"Whether we make plans for the next holiday or whether we just think about what to have for dinner tonight, all of these plans heavily depend on our ability to remember what we wanted to do at the appropriate time in the future," says Diekelmann. "The likelihood that we remember to execute our intentions at the appropriate time in the future is substantially higher if we have had a good night's sleep after having formed the intention."
Diekelmann says that there are two methods for keeping our intentions in mind.
One method is to keep those intentions constantly in mind and be alert to opportunities to execute them. "For example, if I want to drop a letter at the post office on my way to work, I can look for a post office all the way to my work place and think all the time 'I have to drop the letter.'" According to Diekelmann, this method is inefficient—using up cognitive resources necessary for other tasks such as driving or walking without stumbling.
"The second way to remember intentions is to store them in the memory network," she says. "If the memory of the intention is stored well enough, it will come to mind automatically in the appropriate situation."
Diekelmann and her team study this second method. Participants in one of her studies were asked to remember word pairs, and after learning, were told they would have to detect these words in a different task two days later. Half of the participants were allowed to sleep the first night, while half were kept awake. Both groups were allowed to sleep the second night so they would not be tired during testing.
Participants performed a task during testing that included some of the previously learned word pairs. They were not reminded of their intention to recognize the words. Instead, the researchers just recorded how many of the words each participant found. This allowed them to determine whether participants still succeeded in detecting the words when they had to do an additional task at the same time that required their full attention.
"We expected that, if participants had stored the intention sufficiently strong in their memory, then seeing the words should automatically bring to mind the intention to detect the words," Diekelmann says.
Those participants allowed to sleep the first night were able to automatically detect the words.
"With sleep, the participants performed perfectly well and detected almost all of the words even when they had to perform two challenging tasks in parallel," Diekelmann says. The participants who remained awake that first night, however, performed substantially worse in detecting words while performing other tasks.
"Even when we have to do a lot of different things at the same time, sleep ensures that our intentions come to mind spontaneously once we encounter the appropriate situation to execute the intention," Diekelmann says.