Three-month-old infants have better recall when they get a brief nap after learning something new, according to small experiment that suggests sleep may play a role in solidifying memories very early in life.
While previous research has linked frequent naps to better memory in babies as young as 6 months, the current study examined the impact of a single 1.5- to 2-hour nap for infants half that age.
The experiment tested memory by counting on babies to quickly tire of looking at faces they remember. Researchers showed infants one of two cartoon characters with distinctive facial features, let some of the babies nap, then showed all of the babies both characters to see which one captured their attention longer.
More than half of the babies who napped turned their gaze to the unfamiliar cartoon face, indicating they remembered what they saw before they slept, the study found. But without a nap, babies appeared to randomly choose which face they looked at, suggesting they forgot what they had seen before and found both cartoons new and interesting.
“Three month-old babies could only remember the newly shown face if they had a nap right after seeing the new cartoon face,” said lead study author Dr. Klara Horvath, who conducted the study at the University of Oxford in the UK.
“It seems for them having a short period of sleep is necessary to be able to consolidate memories, otherwise they just forget the newly learned information,” Horvath, now a pediatrics researcher at Semmelweis University in Budapest, said by email.
For the study, researchers also looked at something known as sleep spindles, or spikes of brain activity thought to be involved in consolidation of memories. Sleep spindles show up on electroencephalogram (EEG) tests that examine brain wave patterns.
Among babies who napped, infants who also had more sleep spindles appeared to become familiar with the faces more quickly, suggesting that the brief periods of rest might influence how fast the brain processes information, researchers report in Developmental Science.
One limitation of the study is its small size - only 45 infants altogether. There were just 28 babies in the nap group, and only 15 had EEG data.
Another drawback is that all the babies in the nap group saw the cartoon faces right before they went to sleep, making it impossible to rule out the potential for that learning experience to influence the number of sleep spindles, the researchers note.
The study also didn’t find a difference in memory based on the duration of babies’ naps, which suggests that more sleep may not always be best when it comes to learning, said Sabine Seehagen, a psychology researcher at the University of Waikato in New Zealand who wasn’t involved in the study.
“It is possible that some undetermined minimum duration of sleep was all that was needed for infants to ‘succeed’ in the task,” Seehagen said by email. “We also don’t know how effective the nap was compared to, say, a full night’s sleep and we don’t know if several naps might have added benefits.”
Still, the findings offer fresh evidence that sleep is critical to normal development even at a very young age, said Gina Poe, a researcher in physiology and psychiatry at the University of California, Los Angeles, who wasn’t involved in the study.
“We neuroscientists and biopsychologists have a long way to go before we understand how long different types of memory consolidation tasks take and why,” Poe said. “But once the job is done, more sleep may be akin to the builders hammering more nails into a structure that is already securely connected.”
That doesn’t mean that parents should cut short naps to help babies’ development, however.
“Even if the job that you are tracking is done with a short nap, there may be other brain tasks that the brain is attending to during a longer nap that we don’t know about,” Poe added. “So never wake a sleeping baby.”