Scientists have known for some time that sleep helps us to consolidate memories from the previous day.
But new research suggests that while we sleep, the brain works harder to process the memories we value more highly.
In a study at Swansea University, scientists taught 80 non-Welsh speakers a series of Welsh words.
Participants who learned the new vocab earlier in the day were less likely to remember the words than those whose study sessions preceded sleep.
But the scientists also discovered that people in the sleep group who placed a higher value on learning the words were more likely to remember them.
Prof Mark Blagrove, who conducted the research with colleague Elaine van Rijn from Swansea University, told the BBC:
“The mere fact that your beliefs about something seem to affect how the brain processes things during the night is really quite astounding.”
The participants were all native English-speaking students who had recently arrived in Wales to study at university. None had previously lived in the country.
Participants were tasked with recalling the words immediately and then 12 hours later, either with no sleep or at least six hours sleep in between.
In the sleep group, the scientists noted a correlation between those who valued the language and their ability to recall the words.
There was no such correlation in the wake group.
Last month, researchers in France found that people who schedule study sessions around sleep revise more effectively.
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