RST key terms

A continuous overnight recording of brain activity, eye movements, muscle tone, breathing, oxygen level, heart rhythm, and body position used to stage sleep and diagnose sleep disorders.

Recording of electrical activity from scalp electrodes that reveals wakefulness and sleep stages through frequency and waveform patterns such as alpha, theta, and delta activity.

Recording of eye movements using electrodes near the eyes, used to detect slow rolling eye movements of light sleep and the rapid eye movements of REM sleep.

Recording of muscle electrical activity, usually from the chin and legs, used to identify muscle tone changes across sleep stages and to detect limb movements.

The process of scoring each 30-second epoch as wake, N1, N2, N3, or REM using standardized rules applied to EEG, EOG, and EMG recordings.

A fixed 30-second page of polysomnographic recording that serves as the basic unit for assigning a single sleep or wake stage during scoring.

A sharply contoured negative wave followed by a positive component lasting at least half a second, a hallmark of stage N2 sleep often triggered by sound or touch.

A brief burst of 11 to 16 Hz activity lasting at least half a second, characteristic of stage N2 sleep and associated with protection of sleep from disturbance.

Stage N3 sleep, defined by high-amplitude waves slower than 2 Hz occupying at least 20 percent of an epoch; it dominates early sleep and supports restoration and memory consolidation.

A sleep stage with mixed-frequency low-amplitude EEG, episodic rapid eye movements, and very low chin muscle tone, associated with vivid dreaming and memory processing.

The near-absence of skeletal muscle tone during REM sleep caused by active inhibition of motor neurons, which prevents acting out dreams.

The time from lights out to the first scored sleep epoch, a key measure of how quickly a person falls asleep and a common indicator of insomnia or sleepiness.

Total sleep time divided by time in bed, expressed as a percentage, reflecting how much of the bedtime period was actually spent asleep.

The average number of apneas and hypopneas per hour of sleep, used to classify obstructive sleep apnea severity as mild, moderate, or severe.

A partial reduction in airflow during sleep lasting at least ten seconds that meets scoring criteria for amplitude drop and often is accompanied by oxygen desaturation or arousal.

The number of times per hour of sleep that blood oxygen falls by a specified amount, typically three or four percent, reflecting the frequency of respiratory events.

A noninvasive method using light absorption through the skin to estimate arterial oxygen saturation continuously during sleep recordings.

An abrupt shift in EEG frequency lasting at least three seconds during sleep, often reflecting a brief awakening that fragments sleep without full wakefulness.

Repetitive, stereotyped leg movements occurring in series during sleep, detected on leg EMG and often associated with arousals or restless legs syndrome.

A wrist-worn device that records movement over days to estimate sleep-wake patterns, useful for assessing circadian rhythm and sleep schedules outside the laboratory.

A daytime series of nap opportunities measuring how quickly a person falls asleep, used to objectively assess excessive daytime sleepiness and narcolepsy.

A daytime test measuring the ability to remain awake during quiet, sedentary conditions, often used to evaluate treatment response and fitness for safety-sensitive duties.

A limited unattended recording of breathing, oxygen, and effort performed outside a sleep laboratory, used to diagnose obstructive sleep apnea in appropriate patients.

A treatment that delivers pressurized air through a mask to splint the upper airway open, the primary therapy for obstructive sleep apnea.

An internally generated cycle of roughly 24 hours that regulates sleep timing, hormone release, and body temperature, synchronized mainly by light exposure.

The accumulating pressure to sleep that builds with time awake and dissipates during sleep, working with the circadian system to govern alertness across the day.

A hormone released by the pineal gland in darkness that signals biological night and helps time sleep onset; it is used clinically to shift circadian timing.

Persistent difficulty falling asleep, staying asleep, or waking too early despite adequate opportunity, with daytime consequences, often maintained by worry and habits.

A structured, evidence-based treatment combining sleep restriction, stimulus control, cognitive restructuring, and relaxation to improve sleep without medication.

A behavioral instruction set that reserves the bed for sleep and sex, limits time awake in bed, and keeps a consistent wake time to strengthen the bed-sleep association.

A set of general habits and environmental practices, such as regular schedules, limiting caffeine and alcohol, and a dark quiet bedroom, that support healthy sleep.

A neurological disorder of sleep-wake regulation marked by excessive daytime sleepiness and, in type 1, cataplexy, with low hypocretin and early REM sleep.

A sudden, brief loss of muscle tone triggered by strong emotion such as laughter, a defining feature of narcolepsy type 1.

A disorder in which the upper airway repeatedly collapses during sleep, causing airflow reduction, oxygen drops, and arousals that fragment sleep and raise cardiovascular risk.

Cessation of breathing during sleep caused by absent or reduced respiratory effort from the brainstem rather than airway blockage, common in heart failure and with opioids.

A breathing pattern of gradual waxing and waning of tidal volume separated by central apneas, often seen in heart failure and associated with unstable ventilatory control.

The degree to which a patient uses a prescribed therapy such as positive airway pressure for the recommended hours and nights, a major determinant of treatment benefit.

A circadian rhythm disorder in which sleep onset and wake times are shifted later than desired, causing difficulty waking for school or work despite adequate sleep duration.

The cumulative shortfall between sleep needed and sleep obtained, which impairs alertness, mood, and performance and is only repaid by adequate sleep.

Repeated brief awakenings or arousals that break sleep continuity, reducing restorative sleep quality even when total sleep time appears adequate.