According to new research a good nights sleep has more benefits than just making one feel rested.
Researchers at Harvard Medical School say they have discovered new evidence that sleep improves the brain's ability to remember information.
Memory is possibly a person's most distinctive characteristic and defines who we are, and acts as a guide to our present and future.
Memories endure and the loss of memory, because of diseases such as Alzheimer's or as a result of accidental brain damage, is particularly devastating and distressing.
Psychologists have defined normal human memory into procedural and declarative memory.
Procedural memory is used for skills such as how to do something such as riding a bike; while declarative memory is more concerned with knowing that a bicycle is called a bicycle.
Procedural memory persists even in disease states such as Alzheimer's where episodic and semantic memories are progressively lost, which suggests that the ways in which procedural and declarative memories are made and stored may be different.
Lead researcher Jeffrey Ellenbogen a postdoctoral fellow at Harvard's Center for Sleep and Cognition says sleep appears to strengthen memories and makes them resistant to interfering information.
Ellenbogen and colleagues studied the influence of sleep on declarative memory in 60 healthy, college-aged adults who did not use prescription drugs and did not have known sleep disorders or abnormal sleep patterns.
They say their findings indicate that memories of recently learned word pairs are improved if sleep intervenes between learning and testing and that this benefit is most pronounced when memory is challenged by competing information.
There has been a great deal of debate and research on whether sleep helps memory and although most experts agree that sleep promotes learning of certain types of perceptual memories (for example, learning to tap numeric sequences on a keyboard), there is ongoing debate about whether sleep benefits so-called declarative memory.
For the study the group were assigned to one of four groups: sleep before testing, wake before testing, sleep before testing with interference, or wake before testing with interference.
Everyone was asked to memorize 20 paired words; they were tested 12 hours later for recall by completing a cued-recall task.
Those in the interference groups were also given a second list of 20 distracting or interfering word-pairs just before testing which made remembering the first list of word-pairs more difficult.
The researchers found that those who slept between learning and testing were able to recall more of the original words they had learned earlier.
The beneficial influence of sleep was particularly marked when participants were presented with the challenge of "interference"--competing word-pair information--just prior to testing.
Furthermore a subsequent follow-up group further demonstrated that this sleep benefit for memory persisted over the subsequent waking day.
The team say this is clarifies and extends the previous study of sleep and memory by demonstrating that sleep does not just passively and transiently protect memories but does in fact play an active role in memory building and consolidation.
The researchers say the finding may be particularly important for people with mentally demanding lifestyles, such as doctors, medical residents and college students, who often do not get enough sleep.
The report is published in the July 11 issue of Current Biology.