Sleep Distribution Waveform on EEG
Several basic forms of brain electrical activity presented by EEG during sleep
Alpha wave (8-13 times/sec), theta wave (4~7 times/sec), sigma wave (0.5~3 times/sec) and sigma shuttle wave (around 14 times/sec) and “K-complex wave” “.
Several waveforms of EEG
Generally speaking, the wave with fast frequency has a smaller amplitude, while the wave with slow frequency has a larger amplitude. The amplitude of the alpha wave drawn from the adult scalp is in the range of 20-50μu, while the amplitude of the sigma wave is in the range of 20-200u. Therefore, Alpha waves are often referred to as low-amplitude fast waves, while sigma waves are generally referred to as high-amplitude slow waves. “K-complex wave” is a specific type of waveform that appears in the second phase of slow waves, which is composed of large slow waves in negative and positive phases.
Four States of EEG Sleeping
When a person is awake, the cortical EEG activity is dominated by a wave, and the muscle system is accompanied by a high degree of tension. During slow-wave sleep, the cortical brain electrical activity EEG is in the form of a high-amplitude slow wave. During this period, the muscles still maintain a certain degree of tension. This is a kind of light sleep state. Since the EEG is in the form of slow waves during this period, it may be a myriad of cortical layers. Consequences of rhythmic synchronization of neuronal spontaneous electrical activity. The degree of slow wave stage 1-4 sleep ranges from shallow to deep.
The first phase of EEG is nap and light sleep
He still responds to external stimuli, and has many strange experiences, such as body numbness, tremor, swelling, ups and downs, and fragmented thinking activities in the brain, which can be recalled after waking up. , mixed with some β rhythms, generally there should not be spindle waves or K-complex waves, even if there are, their frequency should not exceed once per minute.
The second stage of EEG is moderate sleep
There is no response to external stimuli, and there is no recall of mental activity. The EEG shows a σ-fusiform-complex wave on the background of theta wave activity, and a σ wave can also appear, but the α wave index accounts for 20%. the following.
The third stage of the EEG is moderate to deep sleep
EEG shows high-amplitude (at least 75μU) sigma waves, sigma wave index accounts for 20% to 50%, and there are occasional spindle wave aftertastes.
EEG stage 4 is deep sleep
The EEG presents a large number of sigma waves, and the sigma wave index is above 50%. When a normal person falls asleep, with the deepening of sleep, they experience slow-wave sleep from the first to fourth stages, with uniform breathing and pulse, maintaining muscle tension, and facial features. There is no muscle activity, usually no dreams. This sleep experience lasts 70 to 100 minutes. The sleep goes from the third stage to the fourth stage, and soon, it returns to the third and second stages, and thus turns into deep sleep.
Fast-wave sleep is a deeper sleep than slow-wave sleep, also known as deep sleep. Although it is deep sleep, the characteristics of brain electrical activity are similar to those of waking, so it is also called paradoxical sleep. At this time, the EEG is in the form of a low-amplitude fast wave.
The eye polyelectricity is significantly enhanced, the myoelectricity is significantly weakened, the muscles are completely relaxed, accompanied by rapid eye movements of 50-60 times/min, and a cycle of sleep is completed in 10-30 minutes. After that, switch back to slow-wave sleep, go through the second, third, and fourth stages, then go through the third and second slow-wave sleep, and then enter fast-wave sleep for the second time, and so on for 3 to 6 cycles, ending one night of sleep.
Only in the second half of the night slow-wave sleep gradually decreased or disappeared, while fast-wave sleep time increased. In the whole night’s sleep, slow wave sleep accounts for 75~80% of the time; the first period accounts for 5~10%, the second period accounts for 50%, and the fast wave sleep accounts for 20~25%. During sleep, dreams are mostly reenactment of daytime activities. During the third and fourth fast-wave sleep, most of the dreams appear from past and childhood experiences and situations. During the fifth fast-wave sleep, dreams are both recent and past events. have.
Most of the late fast-wave sleep had dreams (80% of the subjects reported having dreams), while only 7% of those awakened in slow-wave sleep experienced dreams. It should be pointed out that the division of sleep periods is somewhat artificial.
In fact, various sleep stages often overlap and interlace, and it is difficult to find a sharp demarcation point. For example, after falling asleep, in the electrical activity of the brain. The number and amplitude of the waves are gradually increasing. In addition to making a rigid division based on artificial definitions, it is often difficult to clearly distinguish where the boundary between the second and third periods is, and where is the boundary between the third and fourth periods. Gradually from shallow to deep, σ wave gradually from less to more is sure.
Similarly, the physiological characteristics and brain wave characteristics of sleep are more obvious and typical only in the central part of each sleep. Before or after this, REM sleep and the second stage of NREM sleep gradually migrate and penetrate, and it is difficult to determine the specific the demarcation point.
During REM sleep, the arousal threshold of animals is elevated. From this perspective, REM sleep is the deepest stage of sleep, in contrast, humans are more likely to wake up in this stage than other stages. In this measure, human REM sleep is again It is the shallowest stage of sleep, so some phenomena seem to be contradictory. From the point of view of the wake-up threshold, REM sleep is similar to the second wake-up threshold of NREM sleep, and the REM sleep stage is more likely to wake up on its own. In terms of extremely low muscle tone and lack of skin resistance response, REM sleep is very deep, no less than the fourth stage of NREM sleep;
On the other hand, judging from the variability of heart rate during REM sleep and the impulse firing of certain nerve cells in the brain, REM sleep is almost close to an awakening state. Both REM sleep and NREM sleep stage IV decrease with age, especially in infancy and early childhood, and the impact of REM sleep on brain development is particularly striking.