The mechanism by which a good night's sleep improves learning
and memory has been discovered by scientists.
The team in China and the US used advanced microscopy to witness
new connections between brain cells - synapses - forming during sleep.
Their study, published in the
journal Science, showed even intense training could not make up
for lost sleep.
Experts said it was an elegant and significant study, which
uncovered the mechanisms of memory.
It is well known that sleep plays an important role in memory
and learning. But what actually happens inside the brain has been a source of
considerable debate.
Researchers at New York University School of Medicine and Peking
University Shenzhen Graduate School trained mice in a new skill - walking on
top of a rotating rod.
They then looked inside the living brain with a microscope to
see what happened when the animals were either sleeping or sleep deprived.
Their study showed that sleeping mice formed significantly more
new connections between neurons - they were learning more.
A connection between two brain cells
And by disrupting specific phases of sleep, the research group
showed deep or slow-wave sleep was necessary for memory formation.
During this stage, the brain was "replaying" the
activity from earlier in the day.
Prof Wen-Biao Gan, from New York University, told the BBC:
"Finding out sleep promotes new connections between neurons is new, nobody
knew this before.
"We
thought sleep helped, but it could have been other causes, and we show it
really helps to make connections and that in sleep the brain is not quiet, it
is replaying what happened during the day and it seems quite important for
making the connections."
Analysis
This is just the latest piece of science to highlight the
importance of sleep.
A new reason for sleep was discovered last year when experiments
showed the brain used sleep to wash away waste toxins built
up during a hard day's thinking.
However, there are concerns that people are not getting enough
sleep.
As part of the BBC's Day of the Body Clock, Prof Russell Foster
argued that society had
become "supremely arrogant" in ignoring the
importance of sleep, leading to "serious health problems".
These include:
cancer
heart disease
type-2 diabetes
infections
obesity
The reward for more sleep, Prof Foster argues, is we would all
be "better human beings."
Further tests showed how significant sleep
was. Mice doing up to an hour's training
followed by sleep were compared with mice training intensively for three hours
but then sleep deprived.
The difference was still stark, with the sleepers performing better and the brain forming
more new connections.
Prof Gan added: "One of the
implications is for kids studying, if you want to remember something for long
periods you need these connections.
"So it is probably better to study and
have good sleep rather than keep studying."
Commenting on the findings, Dr Raphaelle
Winsky-Sommerer, from the University of Surrey, told the BBC: "This is
very impressive, carefully crafted and using a combination of exquisite
techniques to identify the underlying mechanisms of memory.
"They provide the cellular mechanism
of how sleep contributes to dealing with experiences during the day.
"Basically it tells you sleep promotes
new synaptic connections, so preserve your sleep."
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