Sleep and Memory Consolidation

One year, when I was a teenager, my high school put on the musical Cabaret and I was volunteered into the role of pianist for the show.  I was handed a huge binder containing a piano reduction of the orchestral score and told to go to it.  I accompanied rehearsals, helped weak singers learn their parts, and played in the pit orchestra.  And what was extremely clear to me was that I was not actually a good enough pianist for the job.  That music was hard!  I wasn’t experienced enough to be able to figure out what bits to play and what to leave out, and so struggled along trying to play every single note.

At the end of each day, I would fall into bed exhausted, and every night I would dream I was playing the piano.  Not just some random dream where I was playing: in every dream I was sitting at the piano, looking at the music for Cabaret, actually expending mental energy to play the notes in front of me. 

Sleep and Learning

I hadn’t thought much about that time-period in years, but when I read a recent paper, it all came back to me.  The paper, written by Simmons and Duke in 2006, looked at the role of sleep in solidifying memories.  The researchers taught a simple piano melody to two groups of volunteers.  One group learned the melody in the morning, and was tested to see how well they played it in the evening.  The second group learned the melody in the evening and was tested in the morning.  The results were striking:  the second group (tested in the morning) showed a huge improvement in performance compared to the night before, while the first group showed no improvement.  The only real difference between the groups was that the second group had had a night’s sleep. 

Data from Simmons and Duke (2006).  PM/AM refers to the group that practiced in the evening and was retested in the morning (after sleep).  AM/PM refers to the group that practiced in the morning and was retested in the evening.

Sleep enhances memory consolidation

This study is just one of a number of recent studies showing the role of sleep in memory consolidation.  Consolidation is an important stage of memory formation, in which recently formed memory traces are made resistant to interference, strengthened, and anatomically rearranged in the brain.  Studies have shown that for motor memory, there is definitely consolidation happening during non-REM sleep (the deep sleep when we’re not dreaming).  Sleep deprivation blocks memory consolidation and so sleep-deprived people do not show an improvement in performance the next day.

Role of REM vs. non-REM sleep

But let’s step back a second… I just said that consolidation definitely happens during non-REM sleep, when we’re not dreaming.  But at the beginning of this post I was talking about how much I was dreaming about piano practice.  So what’s the relationship?  Well, non-REM sleep has been shown to be critical for motor sequence learning, when we’re learning a pattern of movements, like learning a particular new song.  So sure, when I was struggling with the piano score for Cabaret, I was learning new songs, and that required non-REM sleep.  But there was so much new music that I was also learning how to sight-read better.  That’s not a new motor memory, that’s a new skill.  Skill learning like that is a form of sensorimotor learning, where we have to take sensory input and translate it into the appropriate motor response.  And that type of learning requires REM sleep, the sleep in which we're dreaming.  When people are intensely learning a new skill or immersed in a new language, the proportion of time they spend in REM sleep has been shown to increase.  And depriving people specifically of REM sleep inhibits their learning.

Playing difficult music day in and day out, like I did with Cabaret, is an intensive learning situation, and probably the repeated dreams I experienced were related to memory consolidation during REM sleep.  I literally was practicing in my sleep.

All of this is to say that sleep (both REM and non-REM) is absolutely critical for stabilizing and improving memories.  Just by sleeping, you can improve your music performance. Getting a good night’s sleep on a regular basis is probably the best thing you can do to improve your ability to learn.