What Happens During Polysomnography?

What Happens During Polysomnography?
At a sleep laboratory, the electrical output from the brain can be measured during sleep by a special machine called a polysomnograph (PSG). The PSG also measures eye movements, muscle tension, breathing, and heart rate (Kryger, Roth, & Dement, 2005).

The PSG shows what happens in the brain and body while a person sleeps. Most sleep laboratories now use computers to record the results of the PSG. These records are then analyzed by a physician that specializes in sleep medicine to determine if sleep is healthy.

Let’s pretend you are hooked up to a polysomnograph, and see what the PSG will show about what happens in your brain while you sleep.

When you are awake with your eyes open, the markings on the computer screen look fast, jagged and uneven. However, when you lie down and close your eyes, the marks change. They look more even and slower, but still sharp. Scientists call these brain waves alpha waves (Kryger, Roth, & Dement, 2005).

Scientists call the first stage of sleep Stage 1. During Stage 1, sleep is light and you are easily awakened. If someone wakes you up, you might not even know that you have been asleep. You might say that you were thinking about something. The marks on the computer screen look a little bit slower, more even, and not so jagged (Kryger, Roth, & Dement, 2005).

During Stage 2, you go into a deeper sleep. If someone wakes you during Stage 2, you will probably know that you have been asleep. The polysomnograph shows special waves. K complexes look a bit like the letter K. Sleep spindles look like short bursts of very fast, sharp waves (Kryger, Roth, & Dement, 2005).

Scientists also call Stages 3 and 4 sleep slow wave sleep. Have people ever told you that they tried to wake you up, but you were so deep asleep that they could not wake you? You were probably in Stage 3 or 4 sleep. During these stages, the polysomnograph shows slow, smooth brain waves. The amplitude, or height, of the brain waves appears to be much greater. Scientists believe that slow wave sleep is particularly important for body growth and repair (Kryger, Roth, & Dement, 2005).

If someone watches you in REM sleep (the fifth stage), he or she will see your eyes move back and forth quickly under your eyelids. REM stands for Rapid Eye Movement. During Stage REM, you have your most vivid, story-like dreams. If someone wakes you during Stage REM, you will probably remember dreaming. Your brain protects you from acting out your dreams by sending out a signal to most of your muscles to keep them from moving. During REM sleep, your brain waves will look much like when you are awake. In order to tell the difference between wakefulness and Stage REM, the person interpreting the PSG will look for rapid eye movement and for lack of muscle tension. REM sleep appears to be especially important for memory and learning (Kryger, Roth, & Dement, 2005).

As you can see, sleep is much more than the absence of being awake. Every night during healthy sleep, your brain goes through five stages of sleep. You cycle through these stages five or six times. You spend all of those hours asleep for good reasons.

Without enough sleep, your body and brain cannot get the rest needed to maintain health and your quality of life. Research suggests that as many as 40% of individuals with neuromuscular disease have a treatable sleep disorder (Calubras, 2005). If you have difficulty sleeping or breathing during sleep, make sure to talk to your physician.


Culebras A., (2005). Sleep and neuromuscular disorders. Neurology Clinics. 23:4, pp 1209-1223. Abstract can be found at https://www.ncbi.nlm.nih.gov/pubmed/16243623

Kryger, M.H., Roth, T., Dement, W.C., (2005). Principles and Practices of Sleep Medicine (Fourth Edition). Elsevier: Philadelphia, PA.

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