1: Shakespeare was right.  

Writing in Macbeth, he tells us sleep is “the chief nourisher in life’s feast.”

Four hundred years later, the science now shows how sleep has a seemingly miraculous effect on our ability to learn and remember. Yesterday, we looked at a controlled experiment in which those who took a nap after doing intensive learning were able to recall 20 percent more information than those who did not.  

What exactly is going on here?  Why does sleep so powerfully impact the learning ability of the human brain?

2: In his book Why We Sleep, Dr. Matthew Walker describes how the hippocampus section of our brain collects our experiences during any given day; it provides “a short-term reservoir, or temporary information store, for accumulating new memories.”

There is a snag, however.  Our hippocampus has a limited storage capacity.  When it’s full, it’s full.

The good news?  While we sleep, inside our brain, there are “short, powerful bursts of electrical activity called sleep spindles,” Matthew writes.  “The more sleep spindles an individual obtained during the nap, the greater the restoration of their learning when they woke up.”

Looking deep into the brain, Matthew and his colleagues are able to see how our sleep modifies the information architecture of our brain: information stored in our short-term memory is moved to a different part of the brain designed for longer-term retention.  

“The pulses kept weaving a path back and forth between the hippocampus, with its short-term, limited storage space, and the far larger, long-term storage site of the cortex (analogous to a large-memory hard drive),” Matthew observes. “In that moment, we had just become privy to an electrical transaction occurring in the quiet secrecy of sleep: one that was shifting fact-based memories from the temporary storage depot (the hippocampus) to a long-term secure vault (the cortex).”

Sleep helps to “future-proof” our memories while “delightfully” clearing out our hippocampus providing “plentiful free space” for new short-term memories.  

“We awake with both yesterday’s experiences safely filed away and having regained [our] short-term storage capacity for new learning throughout that following day. The cycle repeats each day and night,” Matthew notes. “We and other research groups have since repeated this study across a full night of sleep and replicated the same finding: the more sleep spindles an individual has at night, the greater the restoration of overnight learning ability come the next morning.”

3: There is a problem, however, for those of us who do not get enough sleep.

“Of broader societal relevance, the concentration of NREM-sleep spindles is especially rich in the late-morning hours, sandwiched between long periods of REM sleep, Matthew notes. “Sleep six hours or less and you are shortchanging the brain of a learning restoration benefit that is normally performed by sleep spindles.”

More tomorrow.


Reflection:  Am I getting enough sleep?  Do I prioritize sleep?    

Action: Track my sleep over the next two weeks, using a Fitbit, Oura ring, or by manually tracking.

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