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Storage II: Sleep and Memory (Part 7 of 14)

What happens to memories once we make them?  Where do they live?  Why do they last?  More technically: what mechanisms enable us to move memories from working memory into long term memory?  And, what does sleep have to do with all this?
Sleeping and Studying
Some biology will help us out here.

Let’s look for a moment at two important regions of the brain: the cortex, which is the big labyrinthine web of cauliflower in the picture below, and the hippocampus, a much smaller region of the brain deeper into the center of our heads.
Memory and the Brain
The cortex plays a large role in conscious thought and in the processing of information in working memory. 

The hippocampus, however, plays an essential role in the formation of long-term memory, the translation of information from working memory to long-term memory.  In fact, without the hippocampus, we wouldn't be able to make any new long-term memories at all.  (Kind of like the movie "Memento."  Also, there’s a really interesting true story about a man whose hippocampus was removed, and he was thereafter unable to create any new long-term memories.  If you’re interested in this, google “HM psychology.”)

And so here’s the interesting part about the hippocampus, the cortex, and memory:

We’re discovering more and more that sleep plays a significant role in consolidating memory.  An enormous amount of activity happens in these regions during sleep, and it’s been shown to have a significant impact on what happens to our memories in our brains.  

It’s a really exciting area of study right now, and what follows is only a brief entry into the science of sleep.

You may know that we experience sleep in 90-120 minute cycles. Over the course of a night’s sleep, our brains show different patterns of movement, and these patterns occur in fairly predictable cycles.  During some cycles our brains move very quickly, showing tremendous activity.  During others, they move very slowly.

And during these 90-120 minute cycles over the course of a night, the brain performs different tasks:

During hours 1-2, the first hours of sleep, memories are consolidated in the hippocampus, that interior region of the brain, and they are prepared for long-term storage.

During hours 2-6, memories are "moved" to the cortex, where they are kept for long-term memory.  And this means that, on average, if you are getting less than six hours of sleep, then you are not securing that information in long-term memory as well as possible.

But hours 6-9 are when the magic happens: and this is when it gets really cool.  During these hours, the brain actively rehearses memories, replaying them in the cortex during REM sleep.  Some studies have shown that sleeping those extra 2-3 hours can even improve memory performance by up to 25%.

I enjoy telling this to my students: look, without studying any more, you can do better, simply by sleeping!  Your brain actively rehearses what you’ve been working on.  (...of course you have to have understood and studied the material to begin with...)

And, interestingly, it’s not only memory--but also insight and attention.  They all improve with sleep, which really is a topic all its own.
Sleep and Memory

Summary of Storage
And so, storage (memory) has two parts.  We have seen in previous posts that storage is influenced by the intensity and diversity of encoding, and we see here that sleep enhances our storage. 
What makes memories last?
And so, memories are made and strengthened by association, intensity, and repetition.  And they are consolidated and rehearsed during sleep.  This means that as educators, it's helpful to build rich, associative experiences for our students so that their learning is part of an organized network that lasts.  And, the more opportunities we can provide for students to revisit information and then sleep on it, the more opportunities we give them to turn it over in their heads.  Some researchers refer to this practice as "spacing"; if we return to material on separate days--if we leave space between our interactions with it--then we allow students to process what they learn, and this helps maximize their learning.  We'll pick up on this in the next post, on retrieval, the last of the four essential cognitive practices.

Coming up next:  How does retrieval influence memory?  And what can we do to maximize the ease and efficiency of retrieval?

This is the seventh of fourteen posts in a series about the role of cognitive science of education.

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Skull and Sleep images from Wikimedia Commons.

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