Sunday, May 14, 2017

Sleep and Memory Part One

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.


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.

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.
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.


  1. Almost every night as Ben is falling asleep, he has a couple big jolts. Are these what you'd classify as "sleep spindles"?

    Cool post, as usual.

    1. 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.