![]() Intermittent awakening, the amount of time during the night spent in the awake state after being fallen asleep, i.e., the total time spent awake during sleep period time (SPT). The amount of actual sleep time during recording. The duration of time from the start to the end of a recording. The duration of time from “light off” to final awakening. Time spent in each of the sleep stages based on total recording time (TRT). The duration of time from sleep onset (SO) to final awakening. The duration of time from “lights out” to the first epoch of sleep. Time from lights out to the first epoch of sleep. This basic principle of sleep regulation is known as “sleep homeostasis.” Sleep latency Sleep homeostasisĪ sleep deficit elicits a compensatory increase in the intensity and duration of sleep, while excessive sleep reduces sleep propensity. The ratio of total sleep time to time in bed, i.e., TST/TIB × 100. There is a great deal of interindividual variability among people, and duration of sleep cycles, but the overall pattern is generally consistent in the same individual from night to night. In a healthy individual, a typical night of sleep consists of 4–6 sleep cycles of 90–110 min. One complete sleep cycle includes an episode of NREM sleep followed by an episode of REM sleep. Sleep distributed in a cyclic pattern across the night. Later sleep cycles are defined as the periods from the end of an REM sleep episode to the end of the subsequent REM sleep episode. The first sleep cycle is the period from sleep onset to the end of the first REM sleep episode. Sleep architecture can be represented by a graph called a hypnogram. It allows us to produce a picture of what sleep looks like over the course of a night, taking into account various depths of sleep as well as arousals to wakefulness. It represents the cyclical pattern of sleep as it shifts between the different sleep stages, including non-rapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep. Sleep is not a homogeneous state of unconsciousness, but it is characterized by an internal structure, called “sleep architecture,” described by different sleep stages (stage W, stage N1, stage N2, stage N3, and stage R) and transitions among them. The interval between the first epoch of sleep and the appearance of the first REM sleep episode in a recording. REM density is a function that expresses the frequency of eye movements per unit of time during stage REM. Measurement and recording of EEG activity, typically coupled with measurement and recording of cardiorespiratory activity and eye movements, during sleep. The number of occasions of sleep stages shifting from one to another. If REM sleep continues with interruptions by wake or other sleep stages, such REM episodes are considered to be a single REM episode when the interruption is less than 15 min. The number of REM episodes that appear during sleep period time. EpochĪ hypnogram is a graph that represents the stages of sleep as a function of time (Fig. The electrodes are connected to amplifiers and filters that detect, magnify, and record the electrical activity of the brain. During EEG recordings, electrodes are typically placed across multiple scalp regions. EEG is the measurement and recording of the gross electrical activity of the brain. Electroencephalography (EEG)īrain activity obtained as recorded signals from the scalp using electrodes. Sensors normally made of Ag/AgCl that are used to record electro-encephalogram. ArtifactĪccording to the glossary of the International Federation of Clinical Neurophysiology (IFCN), the term artifact is described as “any potential difference due to an extracerebral source, recorded in EEG tracings” and also includes more generally “any modification of the EEG caused by extracerebral factors such as alterations of the media surrounding the brain, instrumental distortion or malfunction, and operational errors.” Electrodes (channels) The number of arousals per hour of sleep.
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