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Sleep stages are characterized by spectral content of EEG: for instance, stage N1 refers to the transition of the brain from alpha waves (common in the awake state) to theta waves, whereas stage N3 (deep or slow-wave sleep) is characterized by the presence of delta waves. [107] The normal order of sleep stages is N1 → N2 → N3 → N2 → REM.
During slow wave sleep, the cortex generates brief periods of activity and inactivity at 0.5–4 Hz, resulting in the generation of the delta waves of slow wave sleep. During this period, the thalamus stops relaying sensory information to the brain, however it continues to produce signals, such as spindle waves, that are sent to its cortical ...
During slow-wave sleep, there is a significant decline in cerebral metabolic rate and cerebral blood flow. The activity falls to about 75 percent of the normal wakefulness level. The regions of the brain that are most active when awake have the highest level of delta waves during slow-wave sleep. This indicates that the rest is geographical.
Gamma waves. A gamma wave or gamma rhythm is a pattern of neural oscillation in humans with a frequency between 30 and 100 Hz, the 40 Hz point being of particular interest. [1] Gamma waves with frequencies between 30 and 70 hertz may be classified as low gamma, and those between 70 and 150 hertz as high gamma.
The electrical activity seen on an EEG represents brain waves. The amplitude of EEG waves at a particular frequency corresponds to various points in the sleep-wake cycle, such as being asleep, being awake, or falling asleep. [18] Alpha, beta, theta, gamma, and delta waves are all seen in the different stages of sleep.
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.
Brainwave entrainment, also referred to as brainwave synchronization or neural entrainment, refers to the observation that brainwaves (large-scale electrical oscillations in the brain) will naturally synchronize to the rhythm of periodic external stimuli, such as flickering lights, [1] speech, [2] music, [3] or tactile stimuli.
In rats, theta wave rhythmicity is easily observed in the hippocampus, but can also be detected in numerous other cortical and subcortical brain structures. Hippocampal theta waves, with a frequency range of 6–10 Hz, appear when a rat is engaged in active motor behavior such as walking or exploratory sniffing, and also during REM sleep. [3]