If you're trying to learn a new word, you may want to sleep on it, a new study suggests.
Researchers taught volunteers new words in the evening and then immediately tested their recall of the words. The deeper the volunteers slept the more words they remembered than they did immediately after learning them.
This improvement was not seen in another group of participants who learned new words and were tested in the morning and re-tested in the evening, with no sleep in between tests.
The brain activity data collected from the volunteers in the sleep group showed that deep sleep (slow-wave sleep) helped strengthen their memories of new words.
The researchers also found that a type of brain activity called sleep spindles played a role in the ability to remember new words. Sleep spindles are brief, but intense bursts of activity that indicate information transfer between two different memory storage areas, the hippocampus and the neocortex.
The more sleep spindles a person experienced during sleep, the more successful they were in using new words in their vocabulary.
"We suspected from previous work that sleep had a role to play in the reorganisation of new memories, but this is the first time we've really been able to observe it in action, and understand the importance of spindle activity in the process," said study co-author Gareth Gaskell, a professor in the psychology department at the University of York in England.
The study was published in the Journal of Neuroscience.