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The descriptive term ultradian is used in sleep research in reference to the 90–120 minute cycling of the sleep stages during human sleep. [ 2 ] There is a circasemidian rhythm in body temperature and cognitive function which is technically ultradian.
Waking is usually characterized by beta (12–30 Hz) and gamma (25–100 Hz) depending on whether there was a peaceful or stressful activity. [22] The onset of sleep involves slowing down of this frequency to the drowsiness of alpha (8–12 Hz) and finally to theta (4–10 Hz) of Stage 1 NREM sleep. [23]
Traditional classification of the frequency bands, that are associated to different functions/states of the brain and consist of delta, theta, alpha, beta and gamma bands. . Due to the limited capabilities of the early experimental/medical setup to record fast frequencies, for historical reason, all oscillations above 30 Hz were considered as high frequency and were difficult to investigate.
2 Hz: 120 bpm, common tempo in music ~7.83 Hz: Fundamental frequency of the Schumann resonances: 10 1: 10 hertz 10 Hz: Cyclic rate of a typical automobile engine at idle (equivalent to 600 rpm) 12 Hz: Acoustic – the lowest possible frequency that a human can hear [3] 18 Hz: Average house cat's purr 24 Hz: Common frame rate of movies 27.5 Hz
The meaning of SMR is not fully understood. Phenomenologically, a person is producing a stronger SMR amplitude when the corresponding sensorimotor areas are idle, e.g. during states of immobility.
The human range is commonly given as 20 to 20,000 Hz, [3] [4] [note 1] although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours.
Persistent sleeping disturbances can lead to fatigue, irritability, and various health issues. Numerous studies have examined the positive impact of music on sleep quality. As early as 2000 B.C., lullabies were designed to aid infant sleep. For adults with sleep-related disorders, music serves as a useful intervention in reducing stress.
Slow-wave sleep (SWS), often referred to as deep sleep, is the third stage of non-rapid eye movement sleep (NREM), where electroencephalography activity is characterised by slow delta waves. [ 2 ] Slow-wave sleep usually lasts between 70 and 90 minutes, taking place during the first hours of the night. [ 3 ]