Eighty non-Welsh speaking participants were taught Welsh words before either a period of wake or sleep.
Those who slept showed an increased ability to learn the words, and the effect was greatest in those who placed personal value on the language.
This suggests that memories perceived as important undergo preferential treatment by the brain during sleep.
While it has long been established that sleep helps the consolidation of memories, this is the first study to show that the effect is influenced by how much you care about the memory.
