The team in China and the US used advanced microscopy to witness new connections between brain cells – synapses – forming during sleep.
Their study, 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.
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.
During this stage, the brain was “replaying” the activity from earlier in the day.
Prof Wen-Biao Said: “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.”
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.
Prof Russell Foster argued that society had become “supremely arrogant” in ignoring the importance of sleep, leading to “serious health problems”.
- Heart disease
- Type-2 diabetes