This headline is based on a small study from the US which examined the effect of a midday nap on children’s ability to recall the location of pictures on a grid, which they had learned that morning when playing a memory game.
The study found that children were better able to recall the location of the pictures later in the day if they had taken a nap in the early afternoon, compared to staying awake throughout the day. Memory was also better the next morning, which the researchers suggest means that the benefits of a daytime nap cannot be made up for with overnight sleep.
The researchers speculate that this improvement may be due to what is known as a sleep spindle. This a burst of brain activity that occurs during sleep which may help the brain ‘integrate’ recent events into the long-term memory (though this hypothesis remains unproven).
Limitations of the study include its small size and the fact that it examined only one type of memory ability (declarative memory, which is the ability to recall previously learned knowledge, such as the nine times table).
With these limitations in mind, the results are intriguing and suggest napping may benefit children in ways that move beyond its impact on attention and afternoon sleepiness.
The study was carried out by researchers from the University
of Amherst in the US and was funded by the US National Institutes of Health and
a research grant from the University’s Commonwealth College.
The study was published in the peer-reviewed journal
Proceedings of the National Academy of Sciences (PNAS). PNAS is an open access journal
so the
study is free to read online or download (PDF, 661Kb).
Both BBC News and The Guardian covered the research
appropriately, including an emphasis on the small study size.
What kind of research was this?
This was a cross-over study that assessed the impact of an
afternoon nap on the memory of preschool children. (These types of study are
usually randomised but this was not the case with this study).
Researchers hypothesised that daytime napping plays a role
in early childhood memory by allowing information gathered during waking hours
to be consolidated (improving the efficiency of recalling stored information)
during short sleeps.
To determine possible mechanisms by which afternoon naps may
exert an effect on memory, the researchers conducted a small laboratory based
study that examined brain activity while the pre-schoolers slept. They
determined that a measure of brain activity during sleep, known as sleep
spindle density, was associated with recall.
What did the research involve?
The research included 77 preschool children between the ages
of 36 and 67 months. Overall, 40 children were included in the analysis. The
children completed a visuospatial task (or less technically, they played a
memory game) in the morning at 10:00am.
The task/game involved learning the position of 9 to 12
pictures displayed in a grid on a screen. The pictures were hidden, one picture
at a time was displayed on the right side of the screen and the children were
asked to locate the same picture in the grid and feedback was provided. This
encoding/playing was continued until the children had successfully identified
75% of the pictures.
Finally, the same memory task was repeated (pictures were
hidden, identical pictures were displayed, children tried to recall where the
matching item was in the grid), this time without feedback, and the children’s
ability to recall picture location was assessed – this served as the baseline
measurement.
Later that day, between 1:00pm and 3:00pm, half of the
children took a nap and half stayed awake. All children then completed the
task/game that afternoon at 3:30pm (delayed recall) and again the next morning
at 10:00am (24 hours recall).
Each child completed both sequences (one day they napped,
another day they stayed awake), and ability to remember picture location was
compared between the two sequences.
The researchers also assessed child-reported sleepiness and
experimenter-rated sleepiness of the children in the afternoons. This was done
in order to assess whether differences in performance on the tests were due to
naps reducing fatigue or increasing attention, rather than memory consolidation
during sleep as hypothesised.
They also examined regularity of child napping, as reported
by parents, to see if the effect differed depending on child sleeping habits.
What were the basic results?
On average, the children spent 78 minutes napping when they
were included in the nap sequence. Performance on the memory test was similar
between the two groups at baseline.
Performance on the delayed recall measurement (at 3:30pm)
and the 24 hour recall were significantly better when the children had napped
than when they had stayed awake:
- baseline
recall accuracy, nap vs. no nap (approximately 76% vs. 75%,)
- delayed
recall accuracy, nap vs. no nap (approximately 77% vs. 64%)
- 24
hour recall accuracy, nap vs. no nap (approximately 78% vs. 63%)
The researchers also found no significant differences in
child-reported sleepiness in the nap vs. no nap conditions. When looking at the
experimenter-rated measures, they found that child sleepiness was greater
following the nap compared to the non-napping sequence.
Further analysis found a difference in effect when analysis
was stratified according to regularity of napping. The positive effect on memory
of the two hour preschool-based nap was greatest amongst the 17 children whose
parents reported that the child napped five or more days each week, while the
10 children who napped on fewer than two days each week saw no benefit.
How did the researchers interpret
the results?
The researchers conclude that an early afternoon nap is
clearly beneficial in terms of memory retention amongst preschool children, and
that the negative effects of missing daytime naps cannot be made up during
night time sleep.
They highlighted the fact that there was a lack of
difference in child-rated sleepiness, and an increase in experimenter rated
sleepiness after naps.
There were also significant differences between the groups
in performance on the 24 hour recall test (conducted after a night’s sleep).
All of the points, they concluded, indicate that the differences in memory are
due to processes during the nap as opposed to indirectly due to its impact on
fatigue and attention.
Conclusion
This small study suggests that afternoon naps may have
benefits in terms of the visual memory of preschool students.
Though there is some uncertainty about the ‘direction’ of
the effects that were assessed by the researchers. It could be the case that a
decline in memory recall ability in regular nappers was due to them being
‘deprived’ of their usual afternoon nap, as opposed to an increase in recall
when additional naps are introduced.
That is, children who napped five or more times a week saw
reductions in recall when they did not nap. While children who napped less than
twice a week saw less decline in recall ability when kept awake during the
early afternoon.
One key limitation of the study is the inclusion in the
analysis of children who completed both the nap and wake conditions. Of the 77
children recruited into the study, 48% were excluded from the analysis because
they were unable to complete either the napping or wake condition, or failed to
complete the memory task, or because their immediate recall (the baseline
measurement) was 100%. This may have introduced selection bias into the
study as the children included in the final analysis may not be truly
representative of their peers.
The authors’ conclusions on the unique process-based
benefits of sleep are supported in part by measures of sleepiness as reported
by experimenters. However, it is unclear if the experimenters were blinded to
whether or not the child had napped during the afternoon; lack of blinding may
have biased the results. Additionally, these measures were not reported to have
been included as part of the statistical analysis, so it is unclear if
significant differences were found based on child fatigue.
The researchers suggest that the results of their sleep
laboratory sub-study suggest that benefits are derived due to processes unique
to sleep. However, this portion of the study specifically recruited children
based on their likelihood to sleep in a lab setting, and thus included mainly
habitual nappers. Whether the findings apply to children who nap infrequently
is unclear based on this study.
This small study assessed the impact of daytime naps on one
specific type of memory. So this cannot be interpreted to mean that napping improves
child memory across the board.
The researchers suggest that their findings should be
considered when making decisions about whether or not to include an early
afternoon sleep session in the nursery or pre-school schedule.
There are no official guidelines about daytime napping, but
the Millpond Children’s Sleep Clinic (an international private sleep clinic
specialising in child sleep problems), recommends that toddlers get around one
hour of sleep during the day. Once a child reaches the age of four they then do
not usually require regular afternoon naps.
Analysis by Bazian. Edited by NHS Choices .
Analysis by Bazian. Edited by NHS Choices .
Article retrieved from: http://www.nhs.uk/news/2013/09September/Pages/Midday-naps-may-boost-toddlers-memory-skills.aspx
Images retrieved from: http://myfunnypics.org/d/6507-1/why+did+you+wake+me+up+this+early.jpg
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