Compared to all the
exciting experiences that happen while we are awake, sleep seems rather forgettable.
But, if we didn’t lie down in the dark to rest each night we wouldn’t be able
to remember anything that happened during our waking hours.
Why?
Even though the body is
still during sleep, the brain is actively working and changing. Part of the
brain’s work is to organize and process memories formed during the day.
Multiple scientific studies on the connection between sleep and memory show that interrupted sleep
damages memory formation, but after a good night’s sleep memories are more
resilient.
There are four stages of
sleep, illustrated in the diagram below.
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| Image by blog author |
Sleep stages occur in cycles starting with N1 sleep and ending with Rapid Eye Movement (REM) sleep. During the night, we go through the sleep cycle four to six times. The first few cycles of the night contain mainly non-REM sleep, specifically N2 and N3 or Slow Wave Sleep (SWS). Later cycles have longer periods of REM sleep.
How do these sleep stages
relate to memory?
Early on, researchers
suspected that REM sleep played the most crucial role of all sleep phases in
memory retention since elements of memories formed during the day often showed
up in dreams, albeit in surreal and unrealistic forms.
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| The Dream by Henri Rousseau. Photo taken by author at the MoMA. |
An early study connecting
REM sleep and memory was conducted by Otto Pöetzl in 1917. Pöetzl briefly showed
his research subjects complex images, such as landscape paintings. He then hid
the image and asked the subjects to report everything they remembered from the
picture. After this exercise, his subjects were instructed to go home and go to
bed. The next day they came back and reported their dreams to Pöetzl. Pöetzl
found that the dreams of his research participants contained elements of the
paintings he showed them the day before, even parts of the image they hadn’t
remembered initially.[1]
Pöetzl’s study, though
not exacting enough for today’s standards, indicated that REM sleep played a
role in memory. What exactly this role was required further study.
Read about modern
research in the role of REM sleep and memory in my next post!
[1] LeDoux,
Joseph. The Emotional Brain: The
Mysterious Underpinnings of Emotional Life. Touchstone Books, published by Simon and Schuster, New York, 1998.
pp. 59-60.
Almost every night as Ben is falling asleep, he has a couple big jolts. Are these what you'd classify as "sleep spindles"?
ReplyDeleteCool post, as usual.
Sleep spindles are rapid brain waves in N2 sleep that I don't think are sensed physically. The jolts that often occur before falling asleep happen during N1 sleep. These jolts are actually where we get the phrase "falling asleep" since they occur when we are just drifting off and are often preceded by the sensation of falling.
DeleteAhhhh makes sense. :)
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