1. Article 7
Sleep: It Does a Memory Good
The most important time for your memory may be when you are
unconscious.
by Kimberly Fenn, Ph.D.
Psychology Today October 15, 2012
You have been creating memories since childhood and ever since you tried
to commit that first fact to memory, you likely discovered ways that you
could improve your memory. For example, if you lived back in the days of
landline phones and phone books, you knew that if you rehearsed a
telephone 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 to
remember it on a subsequent day.
What you may not realize, however, is that your memory can be
strengthened in the absence of such practice. In fact, your memory can be
strengthened even in the absence of consciousness! There is a growing
body 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 of
rest. Instead, your brain is highly active. The nature of this activity is
dependent on the stage of sleep (a topic that will be addressed in future
blogs) but this activity may reflect a form of memory processing.
Psychologists and neuroscientists distinguish between different types of
memory, notably declarative and procedural memory. Declarative memory
is your memory for facts and information (i.e. your memory that the blue
whale is the largest animal in the world) whereas procedural memory is
your memory for skills or habits, such as your ability to do a back flip (if
you are lucky enough to have this skill).
Sleep is beneficial to both forms of memory but the exact benefit afforded
by sleep varies slightly, depending on the type of memory.

2. In our work in procedural memory, we found that sleep has two separate
effects on memory. First, waking activity impairs performance but sleep
stabilizes performance. Merely being awake can negatively impact your
ability 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. In
contrast, sleep stabilizes performance. If you learn the exact same skill in
the evening, then your performance is nearly identical the following
morning. This means that although a long interval has elapsed, you do not
lose any of your learning. Even more exciting, sleep can reverse the
damage caused by waking activity. After a night of sleep, skill memory that
appeared to have been lost is restored. Sleep therefore confers a distinct
advantage to procedural memory; the time at which you learn makes no
difference, as long as you sleep afterward. You can learn a skill in the
morning, or in the evening, and your performance will be roughly the same
the next day.
Sleep also strengthens memory for declarative information but the benefits
are limited. We, along with several other researchers, have shown that
memory for pairs of words (i.e. Cobra-Legs) is better after sleep than after
an equal waking interval. This is similar to the findings in procedural
memory; however, there is one very clear difference in how sleep affects
declarative memory. In declarative memory, waking activity can
permanently impair memory. Memory for information that is acquired in
the morning is significantly worse after 24-hours than information that is
acquired 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 and
performance will be restored! But, if you’re trying to memorize the
periodic table, then you might want to study at night to optimize the benefit
you receive from sleep.