It was reported that previous studies had established the benefits of sleep for non-declarative memories, like the steps of learning to tap numeric sequences on a keyboard. It was explained that the new experiment focuses on the declarative memory like those used for recalling the facts for a test, where in the brain's hippocampus is involved.
Dr. Jeffrey Ellenbogen of Harvard Medical School in Boston and his colleagues had conducted the study on 48 healthy adults aged 18 to 39 who had no sleep problems. They had designed their study so as to test whether sleep helps to build and maintain memory and in overcoming interference, which was explained as the trend of forgetting something else when learning a new piece of information.
The researchers made the participants to memorize 20 pairs of words and were later tested on their ability to recall them. The researchers divided the participants into four groups, mainly sleep before testing, wake before testing, sleep before testing with interference, or wake before testing with interference. In this case, the interference or distraction was a second list of word pairs that participants were supposed to try to ignore during testing.
The researchers found that those who slept between learning and testing were able to recall more of the original words as compared with those who didn't get any sleep. They explained in the online issue of the journal Current Biology on Tuesday, that the beneficial effect was even more obvious when compared between the sleep-interference group, with an average recall of 76%, and the wake-interference group at 32%.
Stating that, "This is the first study to demonstrate that sleep protects declarative memories from associative interference in the subsequent day," the researchers wrote, explaining further that sleep plays an active role in declarative-memory consolidation. The researchers further stated that the results add to the evidence that supports the role that sleep plays in declarative memory, which is based on studies on the brain imaging of animals.