Glossary

Actigraph: A wrist-watch like biomedical device that is used in measuring body movement. The data from the device is used to determine approximate sleep and wake times.

Advanced Sleep Phase Syndrome (ASPS): This is a circadian rhythm sleep disorder. Phases of the daily sleep/wake cycle are advanced with respect to clock time. Here, the sleep phase occurs well ahead of the conventional bedtime and the tendency is to wake up too early. It is more commonly seen in the elderly population.

Apnea: An apnea is a period of time lasting for ten seconds or more during which breathing stops during sleep. There are two types of apneas, the more common obstructive sleep apnea and the less common central sleep apnea.

Bright-light therapy: A form of treatment often used in circadian rhythm sleep disorders and seasonal affective disorders. Exposure to bright, broad spectrum light is used. The timing of light exposure can shift the sleep period in the desired direction i.e. delaying or advancing.

Bruxism: Grinding or clenching of the teeth during sleep.

Cataplexy: Loss of muscle tone that leads to feelings of weakness and/or loss of voluntary muscle control. These episodes are often precipitated by strong emotions such as laughter, anger or excitement. Cataplexy is characteristic of narcolepsy.

Central sleep apnea: A type of sleep apnea in which the airway is not blocked but the brain fails to signal the muscles to breathe. This is often seen in patients with heart failure and kidney failure.

Cheyne-Stokes breathing: A pattern of breathing with gradual increase followed by a decrease in breathing resulting in apnea.

Chronotherapy: A form of treatment for circadian rhythm sleep disorders. The bedtime is systematically adjusted over several days until the desired sleep/wake schedule is achieved.

Circadian rhythms: These are biological rhythms under the control of suprachiasmatic nucleus (also known as “internal clock”) that influences the timing and duration of sleep and also many more physiological functions of the body including body temperature, secretion of certain hormones, etc.

Cognitive behavioral therapy (CBT): A psychological therapy that is aimed at identifying and correcting maladaptive thoughts and beliefs. Relaxation is a key component of behavioral therapy. CBT is often used in the treatment of insomnia.

CPAP (continuous positive airway pressure): A very effective treatment for sleep apnea, it delivers air at a higher pressure to prevent collapse of airways when asleep.

Delayed Sleep Phase Syndrome: This is a circadian rhythm sleep disorder. Phases of the daily sleep/wake cycle are delayed with respect to clock time. Here, the sleep phase occurs well beyond the conventional bedtime and the tendency is to wake up late in the morning or early afternoon. It is more commonly seen in adolescents and young adults.

Delta sleep: Also known as slow-wave sleep or deep sleep, it is the stage 3 of NREM sleep.

Epworth Sleepiness Scale (ESS): A self administered questionnaire used to determine the severity of daytime sleepiness in day-to-day situations.

Gamma-aminobutyric acid (GABA): It is an amino acid and a neurotransmitter in the central nervous system that regulates various physiological functions including sleep.

Hypnagogic Hallucinations: Hallucinations occurring during transition from wakefulness to sleep or at sleep onset.

Hypnogram: A pictorial representation of NREM-REM sleep stages and sleep cycles.

Hypnopompic Hallucinations: Hallucinations occurring during transition from sleep to wakefulness or at sleep offset.

Insomnia: Difficulty with either falling asleep, staying asleep, early morning awakening or non-restorative sleep despite adequate opportunity to sleep.

Jet lag: A condition resulting when travel across time zones leaves a person feeling "out of sync" with the local time at the destination.

Karolinska Sleepiness Scale: A questionnaire used to assess the degree of alertness or sleepiness felt at the time the questionnaire is completed.

Maintenance of wakefulness test (MWT): A sleep test that measures the ability to remain awake in a non-stimulating environment.

Mean sleep latency test (MSLT): A sleep test that measures the ability to fall asleep in a sleep promoting environment.

Melatonin: a neuro-hormone produced by the pineal gland. It is involved in the regulation of circadian rhythms.

Narcolepsy: A sleep disorder characterized by severe excessive daytime sleepiness, cataplexy, sleep paralysis, and hypnagogic/hypnopompic hallucinations.

Night terror: A childhood sleep disorder in which a child wakes up screaming with fright.

Nightmare: A fearful, terrifying dream.

Nocturnal enuresis (bed wetting): Urination during sleep; often seen in children.

Non-rapid eye movement (NREM) sleep: One of the two basic states of sleep. It consists of stages 1, 2 (light sleep) and 3 (deep sleep).

Obstructive sleep apnea (OSA): Sleep apnea caused by a blockage of the upper airway. It is much more common compared to central sleep apnea.

Parasomnias: Abnormal behaviors that occur during sleep that interrupt sleep and can result in injury, insomnia, and/or excessive daytime sleepiness.

Periodic limb movement disorder (PLMD): A disorder in which rhythmic jerking of the legs interrupts sleep, causing insomnia and/or excessive daytime sleepiness and daytime impairments.

Polysomnography: A sleep test that records sleep architecture and a variety of other body functions during sleep, including breathing patterns, heart rhythms, and limb movements.

Progressive muscle relaxation (PMR): This is a relaxation technique that involves tensing and relaxing muscles of the body in a particular order (usually starting at the toes and moving upward toward the head), ultimately to achieve relaxation of the whole body. It is often used as part of relaxation in the treatment of insomnia.

Rapid eye movement (REM) sleep: This is one of the two basic states of sleep. Also known as "dream sleep," it is characterized by rapid eye movements, and more irregular breathing and heart rate compared to NREM sleep.

Rebound insomnia: Insomnia that is worse than before treatment with sedative substances.

Restless legs syndrome (RLS): A neurological condition characterized by unpleasant sensations in the legs accompanied by an irresistible urge to move. Symptoms start or worsen at rest, and decrease when legs are moved/stretched. They are usually worse in the evening especially when lying down, and may interfere with falling asleep. Most people with RLS also have leg jerks while asleep.

Sexsomnia: A type of parasomnia characterized by sexual and sometimes violent acts towards the bed partner.

Sleep apnea: A sleep disorder that occurs when a person’s breathing is interrupted during sleep.

Sleep architecture: Sleep architecture represents the structure of sleep and is generally composed of a cyclical pattern of the various NREM and REM sleep stages.

Sleep cycle: A sequence of sleep stages that usually begins with a period of NREM sleep followed by REM sleep. Each cycle lasts for approximately 80 to 110 minutes and it is repeated four to six times each night.

Sleep deprivation: Lack of sleep over a period of time resulting in physical or psychiatric symptoms affecting day-to-day functions.

Sleep hygiene: A set of practices, habits, and environmental factors that are important for getting a good night sleep.

Sleep latency: the duration of time required to fall asleep after going to bed.

Sleep onset: the transition from awake to asleep.

Sleep paralysis: A temporary inability to move or speak while falling asleep or waking up, often seen in narcolepsy but also seen after sleep deprivation and other sleep disorders.

Sleep talking (somniloquy): A parasomnia characterized by talking in sleep. It originates from NREM sleep.

Somnambulism (sleep walking): A parasomnia characterized by walking in sleep. Often seen in children, it originates from NREM sleep.

Suprachiasmatic nucleus (SCN): A structure in the human brain that is also known as “internal clock”. It regulates sleep and wake in addition to various other physiological functions.