Glossary of Sleep Terms
biological clock – Consists of the control and timing mechanisms for each 24 hour period. Housed in the suprachiasmatic nuclei.
clock-dependent alerting – Signals from the biological clock that tell a person how alert to be throughout the day. Generally highest alerting in evenings and mornings, while lowest in mid-afternoon and throughout the late night.
consciousness – The part of the human mind that is at the level of awareness. It was believed for quite some time that sleep was the ending point of consciousness, but with more research of dreaming, especially lucid dreaming, we now know that is not true.
dreaming – a vivid, complex, hallucinatory experience during sleep generally regarded as real by the dreamer
electroencephalography (EEG) – Brain wave activity used to measure sleep patterns.
electro-oculogram (EOG) – Uses the positive charge of the cornea and the negative charge of the retina to measure eye movements during sleep.
free-running circadian rhythm – when a person is isolated from day and night cues, such as lightness and darkness) their circadian rhythm lengthens slightly and is known as free-running
hypnagogic imagery – Images that become part of a person’s brain activity right around the onset of sleep.
hypnic jerks – See “sleep starts.”
hypnic myoclonias – See “sleep starts.”
hypnopompic – Refers to the period of time when a person is waking up.
minimal units of sleep – People with sleep apnea and other sleep disorders often achieve sleep in very small fragments (1 or two minutes) throughout the night before awakening and falling back asleep again. These minimal units, even if they add up to the sleep need, will still leave the sleeper tired and sleep indebted the following day because they don’t seem to carry enough regenerative power.
multiple sleep latency test (MSLT) – Most widely accepted and objective test to measure the strength of daytime sleep tendency. Measures the speed of falling asleep in a regulated environment at five times during the day, at two hour intervals.
extended MSLT – Evaluates sleep tendency in the evening as well as the daytime by adding two more measurements, making a total of 7 tests.
non-REM sleep – One of the two main stages of sleep. Characterized by lack of rapid eye movements and low muscle activity. There are four stages of non-REM sleep.
opponent process model – the constant interaction of clock-dependant alerting and sleep homeostasis that produces the daily cycle of sleep and wakefulness. In other words, this determines why people fall asleep or are awake at any given time of day, depending on which impulse is stronger.
perceptual disengagement – One of the two essential defining characteristics of sleep. When we are asleep we have virtually no sense of the things around us and the sights, smells, and sounds that we readily perceive during the waking state are not recognized.
Psychomotor Vigilance Test (PVT) – Developed by Dr. David Dinges, this short 10 minute test measures a person’s fitness to perform tasks by having them watch a screen and press a button whenever they see a flash of light.
psychophysiology of dreaming – The relationship of mental and physical activities during dreaming.
REM behavior disorder – A sleeping disorder where a person’s atonia system does not function properly, leaving them unparalyzed during REM sleep and enabling them to physically act out their dreams, often in a dangerous manner.
REM sleep – Stage of sleep where dreams and rapid eye movements occur. The brain is highly active and the body is virtually paralyzed.
REM sleep paralysis – The body’s way of preventing a sleeper from acting out their dreams in REM sleep. Directions from the brain are blocked from going to the rest of the body by the atonia system.
retrograde amnesia – The forgetting of events that happen just before falling asleep, or in the middle of the night. Caused by the body’s inability to turn short-term memories into long-term memories at this time.
reversibility – One of the two essential defining characteristics of sleep. As sleep becomes deeper the awakening stimulus must be increasingly stronger to wake the sleeper up.
sleep crisis – occurs when someone is severely sleep deprived to the point where serious damage to health or safety can occur
sleep debt – Accumulative amount of sleep obtained less that a person’s sleep need.
sleep homeostasis – Process by which our sleep tendency goes up when we don’t have enough sleep and goes down after we obtain sleep.
sleep inertia – Confusion, lack of fine motor skils, and grogginess that occurs immediately following an abrubt awakening
sleep need – Amount of sleep necessary to achieve full and static alertness in the daytime.
sleep onset – When wakefulness changes to sleep, characterized by the end of enhanced alpha rhythms in the EEG.
sleep starts – Also called hypnic myoclonias or hypnic jerks, sleep starts are contraction jerks of the muscles of a sleeper usually occurring within the first 5 minutes of sleep onset. They are often related to the sensation of falling some people have right before sleep onset.
sleep tendency – The propensity to fall asleep at any time of the day defined by the speed one falls asleep. Used for doing sleep latency tests.
suprachiasmatic nuclei – Two small clusters of neurons at the base of the brain that somehow control every person’s biological clock, regulating circadian rhythms.
