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Hypnogogic Hypersynchrony

This is an EEG sample of a 4 year old with jerking in sleep. What do you see?


At first glance, this may seem alarming. Why? Because this activity is soo different from the rest of the sample. Now we have to determine if this is ictal or artifact.

How do we do we determine abnormal activity?

  • What's the patients' age? 4years old

  • What's the level of consciousness? Drowsy tipping into N1

  • Where is this activity happening? Generalized in all channels

  • Is this normal or abnormal? Normal

  • How do we know? The activity is extremely fast, indicating that muscle artifact is a component of this pattern. The age and background for this patient with a drowsy to N1 level of consciousness suggests a normal sleep pattern. Video (not shown in this sample) shows the patient jerking during this event.

What is Hypnogogic Hypersynchrony (Hypnic Myoclonus)?

Sleep jerks or Sleep Myoclonus - a sudden contraction of muscles during sleep transitions. Hypnogogic Hypersynchrony relates to the the transition from awake to sleep. While Hypnopompic Hypersynchrony is related to the transition from asleep to awake.

What causes Hypnogogic Hypersynchrony?

Sleep deprivation and stress are some of the most common causes of sleep jerks (hypnogogic hypersynchrony). This is also a common activation for EEG especially in children. When doing an EEG especially in children, we ask that they prepare by being sleep deprived. Sleep deprivation can also cause stress especially in a 4 year old that is sleep deprived!

Most often when someone experiences a "sleep jerk" they often remember a vivid dream or other sensations like falling or flashing lights. Some sleep myoclonus can be stimulated much like a K-complex with sound association. Have you ever had a dream where you are falling and suddenly jerk awake? The sample above is what happens in the brain waves when this happens.

Is this an indicator of illness or cerebral dysfunction?

While there are several forms of myoclonus (jerking), Hypnogogic Hypersynchrony is benign. It is a normal sleep transition that can happen to anyone. With that being said, excessive sleep interruptions are not healthy for anyone. Frequent arousals like this can lead to broader health concerns. For more information on sleep deprivation you can visit the link below.

Why does this look so scary?

At first glance, especially if you are learning or a an experienced technician, pattern recognition can really test your confidence and skills. As experience tells us, go back to the basics. Just because this looks different doesn't mean "abnormal". Picture a nice quiet, dark lab. Your patient is all cozy and starting to drift off to sleep. and then this jumps off the epoch and your patient jerks or flails. We automatically think "clinical correlation", that must be abnormal. When in fact the EEG goes right back to that normal state and there's no decrement or post ictal phase should be the first clue that this is normal. The speed and generalized activity would also suggest muscle artifact. Knowing what is normal helps us identify abnormal easily. Although this is a normal EEG pattern, you will not see it on every test.





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