Article 7Sleep: It Does a Memory GoodThe most important time for your memory may be when you areunconscious.by Kimberly Fenn, Ph.D.Psychology Today October 15, 2012You have been creating memories since childhood and ever since you triedto commit that first fact to memory, you likely discovered ways that youcould improve your memory. For example, if you lived back in the days oflandline phones and phone books, you knew that if you rehearsed atelephone number over and over in your head, then you would remember it.And the more times you said it to yourself, the more likely you were toremember it on a subsequent day.What you may not realize, however, is that your memory can bestrengthened in the absence of such practice. In fact, your memory can bestrengthened even in the absence of consciousness! There is a growingbody of literature that has shown that memory is improved during sleep.It turns out that when you go to sleep, your brain does not enter into state ofrest. Instead, your brain is highly active. The nature of this activity isdependent on the stage of sleep (a topic that will be addressed in futureblogs) but this activity may reflect a form of memory processing.Psychologists and neuroscientists distinguish between different types ofmemory, notably declarative and procedural memory. Declarative memoryis your memory for facts and information (i.e. your memory that the bluewhale is the largest animal in the world) whereas procedural memory isyour memory for skills or habits, such as your ability to do a back flip (ifyou are lucky enough to have this skill).Sleep is beneficial to both forms of memory but the exact benefit affordedby sleep varies slightly, depending on the type of memory.
In our work in procedural memory, we found that sleep has two separateeffects on memory. First, waking activity impairs performance but sleepstabilizes performance. Merely being awake can negatively impact yourability to perform a new skill. Therefore, if you learn a skill in the morning,then you may lose about half of what you learned by the evening. Incontrast, sleep stabilizes performance. If you learn the exact same skill inthe evening, then your performance is nearly identical the followingmorning. This means that although a long interval has elapsed, you do notlose any of your learning. Even more exciting, sleep can reverse thedamage caused by waking activity. After a night of sleep, skill memory thatappeared to have been lost is restored. Sleep therefore confers a distinctadvantage to procedural memory; the time at which you learn makes nodifference, as long as you sleep afterward. You can learn a skill in themorning, or in the evening, and your performance will be roughly the samethe next day.Sleep also strengthens memory for declarative information but the benefitsare limited. We, along with several other researchers, have shown thatmemory for pairs of words (i.e. Cobra-Legs) is better after sleep than afteran equal waking interval. This is similar to the findings in proceduralmemory; however, there is one very clear difference in how sleep affectsdeclarative memory. In declarative memory, waking activity canpermanently impair memory. Memory for information that is acquired inthe morning is significantly worse after 24-hours than information that isacquired in the evening.To sum it up, if you are trying to learn to surf or to learn a new piano piece,don’t worry if you seem to be getting worse with time – just sleep andperformance will be restored! But, if you’re trying to memorize theperiodic table, then you might want to study at night to optimize the benefityou receive from sleep.