ere at Neurology Associates, we understand that many patients can feel overwhelmed by the use of medical terminology. That is why we make this "Medical Terminology Dictionary" available for your use! We hope you enjoy!

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Click on one of the letters above to jump straight to that portion of the dictionary!


Advanced Sleep Phase Syndrome	A circadian rhythm disorder in which phases of the daily sleep/wake cycle are advanced with respect to clock time. The sleep phase occurs well ahead of conventional bedtime, creating a tendency to fall asleep or wake up too early.

Alpha Rhythm	An EEG brainwave produced when an individual is in a relaxed awake condition with their eyes closed. The frequency is 8-13 Hz in human adults, and is predominately present in the occipital lobe of the brain. It indicates the awake state in most normal individuals.

Alpha Sleep	Sleep in which alpha activity occurs with sleep EEG patterns.

Alpha-Delta Sleep	On rare occasions, Delta brainwaves (deep sleep) are mixed with alpha brainwaves (relaxed wakefulness). Alpha-delta sleep occurs with conditions such as arthritic pain, stimulant use and thyroid imbalance.

Ambulatory Monitor	Portable system used for the continuous recording of multiple physiological variables during sleep.

Amnesia	Loss of memory. Types of amnesia include: anterograde Loss of memory of events that occur after the onset of the etiological condition or agent. retrograde Loss of memory of events that occurred before the onset of the etiological condition or agent.

Apnea	Cessation of breathing for 10 or more seconds during sleep. There are two basic types of sleep apnea: Obstructive Apnea is caused by a closure of the air passage despite efforts to breathe; Central Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most common type. True apnea during wakefulness is extremely rare.



Benzodiazepines	Class of sedative medication commonly used to treat anxiety and insomnia.

Beta Activity	Brain waves seen in alert wakefulness which have a frequency greater than 13 Hz (Hertz).


Central Nervous System (CNS)	The brain and spinal cord.

Central Sleep Apnea	A period of at least 10 seconds without airflow, during which no respiratory effort is evident.

Chronotherapy	Treatment of a circadian rhythm sleep disorder by systemically changing sleeping and waking times to reset the patient's biological clock.

Circadian	Any periodicity that is near but not necessarily exactly 24 hours.



Delayed Sleep Phase Syndrome	A circadian rhythm disorder, which in the daily sleep/wake cycle, is delayed with respect to clock time. Accordingly, the sleep phase occurs well after the conventional bedtime. Usually associated with difficulty getting up in the morning.

Diagnostic Sleep Study	Continuous monitoring of several physiological activities in a sleeping individual. Usually carried out to determine the absence or presence of a specific sleep disorder. A diagnostic sleep study can be performed in a sleep disorders center or in a patient's home with portable recording equipment.

Drowsiness, Drowsy	A state of quiet wakefulness that typically occurs prior to sleep onset. If the eyes are closed, diffuse and slowed alpha activity usually is present, which then gives way to early features of stage 1 sleep.

Déjà vu	A paramnesia consisting of the sensation or illusion that one is seeing what one has seen before

Dyslexia	Inability or difficulty in reading, including word-blindness and a tendency to reverse letters and words in reading and writing.

Dyssomnia	Primary disorders of sleep or wakefulness characterized by insomnia or hypersomnia as the major presenting symptom. Dyssomnias are disorders of the amount, quality, or timing of sleep.

Electrocardiography (EKG) (ECG)	Method of measuring the electrical activity of the heart. EKG is continuously recorded in both diagnostic sleep studies and CPAP titration sleep studies.

Electrodes	Small devices that transmit brain waves or other biological electrical signals from a patient to a polysomnograph machine, where the signal is amplified and displayed.

Electroencephalogram (EEG)	A recording of the electrical activity generated by the brain. Brain wave frequencies are expressed in hertz (Hz) or cycles per second (cps), and amplitude is expressed in microvolts. Characteristic frequency and amplitude patterns of the activity define which stage of sleep the patient is experiencing. Brain waves are recorded in both diagnostic and CPAP titration sleep studies.

Electromyogram (EMG)	A recording of the electrical activity of the muscles. The absence of very low level of EMG activity indicates the presence of REM sleep. Very high levels can help identify periods of wakefulness. Non-invasive EMG is recorded in both diagnostic and CPAP titration sleep studies.



Fatigue	A feeling of tiredness or weariness usually associated with performance decrements.


GABA (Gamma-Amniobutyric Acid)	A major inhibiting compound (neurotransmitter) in the brain, which is considered to be involved in muscle relaxation, sleep, diminished emotional reaction and sedation. GABA is released in the greatest amount from the cerebral cortex during slow wave sleep.

Gastroesphageal Reflux Disease (GERD)	The flow of stomach acid upwards into the esophagus, which can cause arousals and disrupt sleep.


hypersomnia	Excessive sleepiness, as evidenced by prolonged nocturnal sleep, difficulty maintaining an alert awake state during the day, or undesired daytime sleep episodes. ideas of reference The feeling that casual incidents and external events have a particular and unusual meaning that is specific to the person. This is to be distinguished from a delusion of reference, in which there is a belief that is held with delusional conviction

hypnagogic	Referring to the semiconscious state immediately preceding sleep; may include hallucinations that are of no pathological significance.

hypnopompic	Referring to the state immediately preceding awakening; may include hallucinations that are of no pathological significance.

Hyoid Suspension	Surgical procedure sometimes used in the treatment of sleep apnea or snoring. It is designed to improve the airway behind the base of the tongue. The hyoid bone is located in the neck where some tongue muscles attach. If the hyoid bone containing these muscles is pulled forward in front of the voice box, it can open the airway space behind the tongue. This is performed under local intravenous sedation or general anesthesia, and requires a one or two day hospital stay.

Hypnic Jerk	Sensation of falling, and then "jerking" awake just as one drifts to sleep. It is a normal sensation experienced by many people.


insomnia	A subjective complaint of difficulty falling or staying asleep or poor sleep quality.

initial insomnia	Difficulty in falling asleep.

Inappropriate Sleep Episodes	Periods of sleep that are not planned and often occur in an unsafe situation (i.e., while driving). These episodes are always due to sleep deprivation.

"Intermediary" Sleep Stage"	A term sometimes used for non-REM stage 2 sleep.


Jet Lag	A disturbance induced by a major rapid shift in environmental time during travel to a new time zone. Symptoms include fatigue, sleep and impaired alertness.


K Complex	An EEG waveform most commonly found in stage 2 sleep. It has a well-delineated negative sharp wave that is immediately followed by a slower positive component.


Leg Movement	Leg movements are recorded in diagnostic sleep studies to test for Periodic Limb Movement Disorder.

Limit-Setting Sleep Disorder	Occurs when a child stalls or refuses to go to bed, and subsequently does not receive enough sleep.

Linear Sleepiness Rating Scale	A measure of subjective sleepiness. The scale consists of a horizontal line, 100 mm in length on which the right extreme is labeled "Very Sleepy" and the left extreme is labeled "Very Wide Awake."


Middle insomnia	Awakening in the middle of the night followed by eventually falling back to sleep, but with difficulty.

Melatonin	A hormone secreted by the pineal gland in the brain. Melatonin has been reported to have hypnotic properties, leading some to suggest that melatonin, which is released at night, may be an endogenous sleep inducer.

Multiple Sleep Latency Test (MSLT)	The standard test used to quantify the overall daytime sleep tendency by measuring the speed of falling asleep (sleep latency) usually in 5 tests carried out at two-hour intervals. This test also helps in the diagnosis of narcolepsy. Patients with narcolepsy often go directly from wakefulness to REM, which can be evaluated with the MSLT.

Narcolepsy	A sleep disorder characterized by excessive sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations, and an abnormal tendency to pass directly into REM sleep from wakefulness. It was recently found to be caused by an abnormal gene in the brain.

National Commission on Sleep Disorders Research	Created by the U.S. Congress in 1990, the commission conducted a comprehensive study of the social and economic impact of sleep disorders in America, and made recommendations based on its findings to Congress in January of 1993.

Neurology	A specialized branch of medicine that deals specifically with the nervous system and its diseases.

Neurotransmitters	Endogenous chemical components that are released from axon terminals of one neuron and transmit the signal to the next neuron by combining with its receptor molecules. Examples of neurotransmitters that appear to be important in the control of sleep and wakefulness include: norepinephrine, serotonin, acetylcholine, dopamine, adrenaline and histamine. The process of neurotransmission may be inhibited, modulated, or enhanced by other chemical mediators within the brain, or by exogenous pharmaceuticals.

Nightmare	An unpleasant and/or frightening dream that usually awakens a person from REM sleep. Occasionally called a dream anxiety attack, it is not synonymous with a night (sleep) terror.


Obesity-Hypoventilation Syndrome	A term applied to obese individuals who have abnormally slow and shallow respiration (hypoventilation) during wakefulness, resulting in an increased level of carbon dioxide in the blood.

Obstructive Hypopnea	Periodic, partial closure of the throat during sleep resulting in reduced air exchange. The medical consequences of this partial closure can be as severe as sleep apnea (full closure of throat) Usually characterized by snoring, excessive daytime sleepiness, and other symptoms of fatigue

Obstructive Sleep Apnea	Repetitive cessation of breathing during sleep for 10 seconds or more due to complete closure (collapse) of the throat. Usually characterized by snoring, excessive daytime sleepiness, and other symptoms of fatigue.


Paramnesia	A disorder of memory in which dreams or fantasies are confused with reality.

Parasomnia	Abnormal behavior or physiological events occurring during sleep or sleep-wake transitions.

Periodic Limb Movement Disorder	Also known as Periodic Leg Movements of Sleep and Nocturnal Myoclonus. Characterized by periodic episodes of repetitive limb movements during sleep. The movements are often associated with a partial arousal or awakening; however, the patient is usually unaware of the limb movements or frequent sleep disruption. . There can be marked night-to-night variability in the number of movements.

Persistent Insomnia	Continuing insomnia that responds poorly to treatment.

Polysomnogram	A continuous and simultaneous recording of multiple physiological variables during sleep.

Polysomnograph	A biomedical instrument for the measurement of multiple physiological variables of sleep. It records the sleep physiological parameters of EEG, EOG, EMG, EKG, respiratory airflow, respiratory movements, leg movements, and other parameters depending on the situation.


Quiet Sleep	The term frequently used instead of NREM sleep in describing the sleep of infants. Quiet/NREM sleep comprises 50% of a newborns' total sleep time.


Rapid Eye Movement Sleep (REM Sleep)	The sleep stage in which vivid dreaming occurs; identified by the occurrence of rapid eye movements under closed eyelids, motor atonia and low voltage EEG patterns. Also associated with bursts of muscular twitching, irregular breathing, irregular heart rate, and increased autonomic activity.

Restless Legs Syndrome	The sleep disorder characterized by tingling, creeping, crawling, or aching sensation in the legs that tends to occur when an individual is not moving. There is an almost irresistible urge to move the legs that relieve the sensations. Inability to remain at rest can result in severe sleep disturbance.

Restlessness (Referring to Quality of Sleep)	Persistent or recurrent body movements, arousals, or brief awakenings in the course of sleep.


Sleep terror disorder	One of the parasomnias, characterized by panic and confusion when abruptly awakening from sleep. This usually begins with a scream and is accompanied by intense anxiety. The person is often confused and disoriented after awakening. No detailed dream is recalled, and there is amnesia for the episode. Sleep terrors typically occur during the first third of the major sleep episode.

Serotonin	A neurotransmitter in the brain that modulates mood, appetite, sexual activity, aggression, body temperature and sleep.

Sleep	-Overall state in which an individual rests quiescently in a recumbent position, disengages from the environment, and become unresponsive to stimuli.

Sleep Apnea	- Cessation of breathing for 10 or more seconds during sleep. There are two basic types of sleep apnea: Obstructive Apnea is caused by a closure of the air passage despite efforts to breathe; Central Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most common type.

Sleep Architecture	The sequence and duration of each sleep stage and awakening during a sleep period. Often displayed in the form of a histogram.

Sleep Cycle	The progression through an orderly succession of sleep states and stages. In a healthy adult, the first cycle is always initiated by going from wakefulness to non-REM sleep. The first REM period follows the first period of non-REM sleep to complete the first sleep cycle. The two sleep states continue to alternate throughout the night with an average cycle period of about 90 minutes. A full night of normal human sleep will usually consist of 4-6 non-REM/REM sleep cycles.

Sleep Debt	The result of recurrent sleep deprivation that occurs over time, when an individual does not obtain a sufficient amount of restorative daily sleep. Sleep debt is like a monetary debt; it must be paid back at some time. The larger the sleep debt, the stronger the tendency to fall asleep. This accumulation of "lost sleep" may contribute to a decreased quality of life, the onset of related health problems, and the increased risk of injury and/or accident. See Sleep Deprivation.

Sleep Deprivation	An acute or chronic lack of sufficient sleep, which causes a person to feel unrefreshed during wakefulness.

Sleep Disorders	A broad range of illnesses arising from many causes, including; dysfunctional sleep mechanisms, abnormalities in physiological functions during sleep, abnormalities of the biological clock, and sleep disturbances that are induced by external factors.

Sleep Hygiene	Behavioral activities that either contribute to or detract from restorative sleep. Good sleep hygiene would include activities such as going to bed the same time each night, restricting caffeine intake, and avoiding napping during the day.

Snoring	Sounds made during sleep caused by breathing vibrations in the pharynx. In the diagnosis of obstructive sleep apnea, snoring volume and frequency of occurrence often correlate with the severity of the condition. Snoring noise is recorded in both diagnostic sleep studies and CPAP titration studies.


Terminal insomnia	Awakening before one's usual waking time and being unable to return to sleep.

Thoracic Excursion	Thoracic (chest) movement, which indicates respiratory effort. This is recorded in diagnostic sleep studies, and is typically measured by the placement of a sensor band around the chest. The sensor band records chest wall movement associated with respiration. This measurement is used in differentiating the type of sleep apnea.

Transient Insomnia	Difficulty sleeping for only a few nights.


Unintended Sleep Episode	A sleep episode that is not planned and may happen during an activity in which such an episode is hazardous, such as when driving a car or working with machinery.


Wake Time	-The total time scored as wakefulness in a polysomnogram occurring between "lights out" and final awakening.


Zeitgeber	An environmental time cue that entrain biological rhythms to a specific periodicity. Known Zeitgebers are light, melatonin and physical activity. To be effective, these signals must occur when the biological clock is in a responsive phase.

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