show/hide words to know

Electrode: a conductor, such as a piece of metal, used to make electrical contact with some part of a circuit.

Electroencephalogram: visual recording showing the electrical activity of the brain (EEG)... more

NREM sleep: the non-rapid eye movement phase of sleep, during which it can be challenging to wake up.

REM sleep: the rapid eye movement phase of sleep, during which we wake easily....more

Studying Sleep

Sleeping girl

Studying sleep was difficult until equipment was developed to monitor brain waves. "Sleeping girl" painting by Nikolai Dmitriyevich Kuznetsov. Click to enlarge.

Studying sleep is hard. When people are sleeping, we can’t ask how it feels or how their thinking changes because, well, they’re sleeping. Luckily, scientists have invented a clever way of measuring changes in brain activity during sleep.

The Brain Wave Monitor

Most sleep scientists use an electroencephalogram (EEG) to study how the brain changes between waking and the different stages of sleep. Now, “electroencephalogram” is a long word, but we can guess its meaning by breaking down the word into its three parts:

  • Electro – electrical
  • Encephalo – head
  • Gram – a type of message or picture
Cap for EEG

EEG caps that house the wires for all electrodes inside the cap make it easier to record brain activity without interfering with sleep.

If we put the meaning of the three parts of “electroencephalogram” together, we can guess that an EEG is a picture of the electrical signals from the head. Indeed, scientists use EEG machines to monitor electrical brain signals.

The EEG machine records information gathered from electrodes that are attached to a cap worn on the head. Because the process of recording EEGs is not interactive, this method is perfect for studying brain activity during sleep.

What Can EEG Tell Us?

To the untrained eye, an EEG recording looks like a bunch of squiggly lines. However, we can get an idea of how (or if) brain activity changes between wake and different sleep stages by comparing different EEG recordings.

EEG recording

EEG recording showing brain activity when a 21 year old woman was awake. Click for more detail.

To the right is an example of EEG recordings from a 21 year old woman. When you compare the recordings from when she is awake (Wake), in REM sleep (REM), and in NREM sleep (N2, N3), what do you notice?

First, you should notice that none of the EEG recordings are flat lines. This shows that the woman’s brain remains active whether she is awake or asleep. Second, you may notice that the REM and NREM recordings look different from each other. Waves during REM sleep are smaller and more frequent than waves during NREM sleep. This means that your brain is going through different processes during REM sleep than during NREM sleep . And last, you’ll notice that the brain signals look very similar during Wake and REM sleep. This suggests that the brain is actually very active during REM sleep almost as active as when the person is awake and going about their day.

Additional images from Wikimedia Commons.

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Bibliographic details:

  • Article: Studying Sleep
  • Author(s): Sisi Gao, Patrick McGurrin
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: June 21, 2017
  • Date accessed: June 28, 2022
  • Link:

APA Style

Sisi Gao, Patrick McGurrin. (2017, June 21). Studying Sleep. ASU - Ask A Biologist. Retrieved June 28, 2022 from

American Psychological Association. For more info, see

Chicago Manual of Style

Sisi Gao, Patrick McGurrin. "Studying Sleep". ASU - Ask A Biologist. 21 June, 2017.

MLA 2017 Style

Sisi Gao, Patrick McGurrin. "Studying Sleep". ASU - Ask A Biologist. 21 Jun 2017. ASU - Ask A Biologist, Web. 28 Jun 2022.

Modern Language Association, 7th Ed. For more info, see

Learn more about the parts of the brain and what they do in our story A Nervous Journey.

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