"The key to learning and memory in early life is a lengthy nap, say scientists," BBC News reports.
The scientists were interested in babies' abilities to remember activities and events.
They carried out a study involving 216 babies, who took part in trials to see whether napping affected their memory for a new activity.
The babies first watched the researchers taking a mitten off a hand puppet, shaking it, and putting it back on. Half had a nap shortly afterwards and half did not.
Babies who had the nap were able to mimic more of the activities when they played with the hand puppet four hours later. This was also true when the babies were tested 24 hours after being shown the puppets. This may suggest napping shortly after a new activity or event helps to consolidate that memory.
The researchers speculate sleep may help "strengthen" the impact of recent memories as they are stored in the hippocampus, an area of the brain associated with long-term memory retention.
The study suggests napping is important for memory in babies. While sleep is important for memory in adults, this study was only in infants, so you can't use it as an excuse if caught napping at work.
The study was carried out by researchers from the Ruhr University Bochum in Germany and the University of Sheffield.
It was funded by a grant from the Deutsche Forschungsgemeinschaft (German Research Foundation).
The study was published in the peer-reviewed journal, Proceedings of the National Academy of Sciences USA (PNAS).
In general, BBC News reported the story accurately, but its headline doesn't make it clear that the research is in babies.
This was a randomised controlled trial assessing whether napping shortly after being taught a new activity influences how well babies remember how to do that activity.
Previous studies assessing sleep and memory in babies have mostly been observational, and could not determine whether the sleep patterns might be directly influencing memory.
This study overcomes this by directly assessing the impact of napping on developing a specific memory in a controlled experiment.
Randomly allocating the babies into groups is the best way of ensuring the groups are well balanced and the only thing differing between them is whether or not they had a nap.
The researchers enrolled babies aged six months or a year old. The babies were randomly allocated to have a nap or no nap after being taught a new activity involving playing with hand puppets.
They were then tested to see if they could remember and repeat the activity, either four hours later (experiment one) or 24 hours later (experiment two). The researchers then assessed whether the babies who had naps remembered the activity better.
The activity involved the researchers showing the babies a hand puppet wearing a mitten with a bell in it. The researcher removed the mitten from the puppet and shook it to ring the bell to draw attention to the mitten. They then replaced the mitten.
This was all done out of the babies' reach and repeated three times for the year-old babies and six times for the six month olds.
The test involved showing the baby the puppet again, but this time within arm's reach. The researchers recorded if the baby removed the puppet's mitten, attempted to shake the mitten, and attempted to replace the mitten within 90 seconds of being shown the puppet.
The babies scored one point for each of the three actions they tried to replicate. The researchers and parents did not verbally or physically encourage the babies to remove the mitten, and the bell in the mitten had been removed so its sound did not prompt the babies to grab the mitten.
For the "nap" group, the researchers scheduled the activity to occur just before they were about to have a nap. For the "no nap" group, it was scheduled for just after they had had a nap, so they would not be due to have another nap in the next four hours.
A nap was considered as at least 30 minutes of uninterrupted sleep, and the babies wore small motion detectors to see if they were awake or asleep. Caregivers also recorded the babies' sleep patterns. The researchers used both of these sources to assess nap timing and duration.
In the study, caregivers were told not to influence their baby's sleep patterns for the study, and babies whose sleep patterns were not compatible with the group they were assigned to were excluded. This may have unbalanced the groups. Another group of babies were excluded for various reasons, such as tester error.
In their first experiment, the researchers compared the nap and no nap groups with babies who had not been shown the hand puppet activity, but just tested to see what they did naturally when shown the hand puppet.
In total, 120 babies took part in experiment one (test at four hours after hand puppet activity), and 96 babies took part in experiment two (test at 24 hours after hand puppet activity).
They looked at whether nap timing had an impact on how well the baby performed.
The researchers found the babies who took naps shortly after the hand puppet activity were better able to remember it after four and 24 hours.
The researchers say that to their knowledge, this is the first evidence sleep enhances the ability of babies to retain memories of new behaviours in their first year of life.
This study suggests napping shortly after an event may help babies up to the age of one to remember those events.
The study was well designed. The design means differences seen between the groups should be attributable to the naps and not other factors.
The fact some babies were excluded – for example, if they did not have naps as intended – might lead to some imbalances in the groups that could influence results. However, it is difficult to tell if this is the case.
The main assessors of the babies' performance were not blinded as to which group they were in, and therefore could theoretically have influenced results consciously or subconsciously.
However, an independent assessor who was blinded to the groups carried out an assessment of half of the test sessions and showed a high level of agreement with the main assessor. This showed assessor bias was not likely to explain the findings.
Sleep is important for brain function and memory in older children and adults, and this study supports a similar role in younger children.