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Glossary of Sleep Terminology A thru I

Sleep Terminology

If all the terms surrounding sleep can get a little confusing, these definitions may help. (photo credit: BigStockPhoto.com)

Sometimes it can be confusing to understand all of the terms used when talking about sleep. So, we wanted to cover some of the more commonly used sleep terminology.


Actigraphy – The practice of using data about body movement during sleep to determine sleep/wakefulness patterns as part of a sleep assessment.  This test can be done offsite at home using a wrist-watch style actimeter or in a sleep lab.


Advanced Sleep Phase Syndrome – This is a sleep disorder that makes people wake up earlier and fall asleep earlier than the average person.


Alpha Activity – This is the type of brainwave that generally signifies that someone is awake but relaxed.  Often seen in people as they are preparing to fall asleep


Apnea – A period of breathing cessation that can occur during sleep if the airway of the sleeper becomes obstructed.


Benzodiazepine – A type of medication that is frequently used in sleep aids.


Beta Activity – This is the type of brainwave that generally indicates full wakefulness.


Brainwaves – These are the patterns made by the electrical activity in our brains that can be recorded using electroencephalography (EEG).  They can be used to determine where a person is in the sleep/wakefulness cycle.


Caffeine – A stimulant that is found in food and beverages that can interfere with sleep in some people.


Cataplexy – This symptom of narcolepsy involves the abnormal and abrupt paralysis or loss of muscle control in response to strong emotions.


Central Sleep Apnea – A type of sleep apnea that is caused by problems with the respiratory control center in the brain instead of by an obstruction.


Circadian Alerting System – The portion of our “internal clock” devoted to waking us up and a key part of how our sleep is regulated.


Circadian Rhythm – The pattern of day/night variations seen in many biological processes during a 24 hour period.


Circadian Rhythm Sleep Disorder – A sleep disorder that causes the person’s circadian rhythm to be out of synch which can result in a shifting of the person’s sleep cycle which can cause recurrent insomnia and excessive daytime sleepiness.

Cognitive Function – The ability of the brain to think reason, learn, and remember that can be impaired by sleep deprivation.


Continuous Positive Airway Pressure (CPAP) – The primary treatment for obstructive sleep apnea that involves delivering a continuous stream of pressurized air through a mask during sleep to keep the airway open and prevent apneas during sleep.


Cortisol – A hormone secreted by the body most commonly associated with stressful situations that can inhibit sleep.


Delayed Sleep Phase Syndrome (DSPS) – This is a sleep disorder that makes people wake up later and fall asleep later than the average person.


Delta Activity – This is the type of brainwave that generally indicates slow wave sleep or NREM deep sleep.


Diurnal – This term describes things that are active during daylight hours, the opposite of nocturnal.


Electroencephalogram (EEG) or Electroencephalograph – The recording of brainwaves that displays the differences in brain activity during different phases of sleep and wakefulness.


Excessive Daytime Sleepiness – This is a sleep problem resulting from several sleep disorders that can cause difficulty staying awake during the day.


Hypnagogic – This term describes something that happens in the time frame known as sleep onset.


Hypnagogic Hallucinations – These hallucinations occur in the moments just prior to falling asleep and mimic dreams.  They are one of the symptoms of narcolepsy.


Hypnogram – This is a graph that shows the pattern of sleep a person experiences over the course of a night.


Hypnotic – A type of sleep aid or something used in creating a sleep aid that makes the person fall asleep.


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