Babies’ brains do astonishing things during sleep. New research out of Leipzig at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) found that babies can associate meanings to words between six and eight months of age. This skill was previously only seen in older children and adults.
We associate memory with the meaning of words. These memories and meanings pass through the same stages in sleep as they do in lexical development: this personal language development includes things like proto-words that combine both visual and acoustic stimuli to make a word that has a meaning to that person.
For this research, scientists introduced fantasy objects to six- to eight-month-old infants and assigned these objects names like Zuser and Bofel. Similar objects that only differed in minor aspects like color or form were assigned the same names; just as dogs are always dogs, even though they look and act differently. Fantastical objects were used to ensure the infants could not access pre-existing knowledge.
During morning learning studies, the brain’s reaction showed that the babies could not associate or make general relations between similar objects. They were unable to recognize a new Zuser even though it was like other Zusers; however, this changed after a long afternoon nap. Infants who went to sleep after the morning learning sessions could distinguish the terms for new objects, which indicates that their memory consolidated during sleep. Infants who stayed awake during the day or had shorter naps were unable to do this.
The duration of sleep led to one of two types of knowledge development in babies. Following a 30-minute nap, the infants’ brain reaction was similar to that found in a three-month-old's after trying to associate visual and acoustic stimuli. However, the short nap showed they could filter similar object features and connect them to sound, even if the sound has no true meaning.
Infants who took a 50-minute nap saw brain reactions that were only ever seen in adults and older children. The ‘N400’ component happened in these infants’ brains. The N400 component signals when the processed meanings were incompatible, which could be word pairs, picture stores, object-word pairs, or sentences. Scientists used this component to determine that these young infants could learn the meaning of words at this early age.
The research shows that children can consolidate word meanings into their long-term memory a lot earlier than initially assumed. Even though the brain structures for this function are not completely developed, they are already being used to an astonishing extent. Study findings were published in Current Biology.
One sleep stage was particularly important for this process. The second of the four stages seems to influence the development of language memory. Stage two sleep is a lighter sleep, where memories transform from early to advanced development in lexical memory. This transition is comparable to what we see during sleep stages in infant development. In older development, it takes months to move to advanced lexical memory development; in these infants with 50-minute day naps, this transition happened within minutes. Memory consolidation of content takes place fast-paced.
The infants in this study received a lot of information, which would normally be seen or learned over an extended period; however, it is interesting that sleep allows them to disconnect from the outer world to filter and save essential memories. The research indicates that proper sleeping patterns and duration are essential to an infant’s cognitive and language development.
© 2021 American Sleep Association.