A new study published in the Journal of Neuroscience by researchers at the University of York and Harvard Medical School suggests that sleep may help to do both. The scientists found that sleep helps people to remember a newly learned word and incorporate new vocabulary into their "mental lexicon".
During the study, researchers taught volunteers new words in the evening, followed by an immediate test. The volunteers slept overnight in the laboratory while their brain activity was recorded using an electroencephalogram. A test the following morning revealed that they could remember more words than they did immediately after learning them, and they could recognize them faster demonstrating that sleep had strengthened the new memories.
This did not occur in a control group of volunteers who were trained in the morning and re-tested in the evening, with no sleep in between. An examination of the sleep volunteers' brainwaves showed that deep sleep (slow-wave sleep) rather than rapid eye movement (REM) sleep or light sleep helped in strengthening the new memories.
These results highlight the importance of sleep and the underlying brain processes for expanding vocabulary. Lead author Jakke Tamminen, said: "New memories are only really useful if you can connect them to information you already know." he said their study identifies the brain activity during sleep that organizes new memories and makes those vital connections with existing knowledge.