Sleep assists in assimilating new information as well as in recalling memories, a new study by researchers at the University of York and Harvard Medical School has revealed.
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.
he volunteers slept overnight in the laboratory while their brain activity was recorded using an electroencephalogram, or EEG.
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.
When the researchers examined whether the new words had been integrated with existing knowledge in the mental lexicon, they discovered the involvement of a different type of activity in the sleeping brain.
Sleep spindles are brief but intense bursts of brain activity that reflect information transfer between different memory stores in the brain --
the hippocampus deep in the brain and the neocortex, the surface of the brain.
Memories in the hippocampus are stored separately from other memories, while memories in the neocortex are connected to other knowledge.
Volunteers who experienced more sleep spindles overnight were more successful in connecting the new words to the rest of the words in their mental lexicon, suggesting that the new words were communicated from the hippocampus to the neocortex during sleep.
The study has been published in the Journal of Neuroscience.