? Recently, many friends reported that when they woke up in the morning, they saw that there was less deep sleep, especially after midnight, and they were worried that their sleep quality would get worse, or that the monitoring of snail sleep was not accurate now.

In fact, we found that this change is because our algorithm is optimized and the monitoring results are more accurate and reasonable, but this change seems a bit "counterintuitive"! If we compare our sleep report with the professional sleep report used in scientific research literature, we can see that the sleep structure we recorded is more and more in line with human physiological characteristics. Let's compare two pictures first. The first one here is a typical record of snail sleep recently. Deep sleep mainly occurs within 4 hours after falling asleep. The following picture is a record of healthy adults sleeping all night in scientific research papers. Healthy adults sleep about 7-9 hours a day on average, and the total length of deep NREM sleep does not exceed 15%-20% of the "total night sleep time", that is, 1-2 hours.

Record the results of data interpretation by professional sleep monitoring equipment PSG (polysomnography) and sleep technicians. The data shows that deep sleep basically occurs within 4 hours after falling asleep. After the optimization of the algorithm, the analysis report of snail sleep is more and more close to the results of scientific research and clinic.

(The picture is taken from the overnight sleep of a 36-year-old healthy man recorded in the conference paper "Development of Household Wearable Life Sensor Sleep Monitoring System" in Eilat, Takuji Suzuki on June 5438+ 10, 2009. Chinese in the picture is marked as the author's note. )

You may be confused. Since Snail Sleep doesn't distribute PSG devices to users, how can we achieve the effect similar to professional sleep analysis on a mobile phone? In fact, the answer is simple,

First of all, this is the result of continuous optimization by using the method of deep learning, which truly embodies the belief that "technology improves sleep".

Secondly, I would also like to thank the snail sleeping friends, who are not shouting slogans in vain, but "do it yourself" and provide training materials for machine learning with their subjective and objective sleep data.

? In our office, there is a set of PSG equipment that comes standard in the sleep lab. At night, it often becomes the Alpha Lab. Our dedicated friends stick electrodes on their heads, connect wires, and simultaneously collect data with various bracelets, mobile phones, sensors and so on. After data collection, we asked medical technicians with international sleep analysis certification and rich clinical experience to interpret the data for us. Then, these results can become qualified "samples" of machine learning. As for how the computer fits the data collected by various sensors with PSG results, it is said that this is a black box, which humans don't really understand, but the more data, the better it will learn. Today, we feel that our algorithm is really smarter than before.

However, we will not easily stop at the conclusions given by the machine. In addition to PSG objective monitoring, we will constantly compare our "subjective estimation" with the optimized algorithm. In this process, the first thing we observe is that the judgment of waking up at night is getting more and more accurate, which is easy to understand, because although people don't know when their deep sleep happened, it is not too difficult to remember how many times they woke up. Until recent months, our deep sleep has become more and more reasonable. At present, the latitude and accuracy of snoring analysis are also improving. In the future, you may not only hear your own snoring, but also learn more about the results of respiratory dynamics. Worms really don't pretend to care about your sleep. Whether it is a monitoring tool or a perfect content, the standard guide and frontier progress of sleep science are our reference.

The change of old and new reports has caused some confusion to everyone, probably because we usually ignore the introduction of sleep physiology knowledge. Today, we will explain the relevant content in depth from two aspects:

Deep sleep, shallow sleep and sleep cycle

Humans can study sleep deeply, thanks to the invention of electroencephalograph more than 90 years ago. In the 1950s, Aselinski, a scholar at the University of Chicago and his tutor Professor Cleitman found that during sleep, there was a special state in the brain that was very similar to the EEG activity during waking, accompanied by rapid eye movement. There are two types of human sleep, namely non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep.

What we usually call deep sleep and shallow sleep are both stages in the process of sleep. Talking about its depth and shallowness may describe the difficulty of awakening a person more intuitively. In the shallow sleep stage, a little noise in the environment may wake people up, while in the deep sleep stage, whether you wake up loudly or nudge your body, you may wake people up at once. But in physiology, strictly distinguishing each sleep stage actually depends on recording different EEG rhythms in the brain. Usually, we say that shallow sleep is shallow NREM sleep, which includes two stages: N 1 and N2. Deep sleep is deep NREM sleep, also known as N3 stage, or slow-wave sleep. In addition, we also have a dream sleep stage, REM sleep. At this stage, our brain is similar to waking state, but our body is almost paralyzed, so it is also called "contradictory sleep".

This is the signal diagram used by the sleep laboratory to record the sleep stage, in which the red box marks the eye movement of rapid eye movement sleep. )

In scientific research and clinical field, PSG (polysomnography) can obtain the data of EEG, eye movement signal, EMG signal and respiratory heart rate through dozens of leads without affecting people's sleep, so that we can know four sleep stages with different physiological characteristics and functions of normal people: 1) shallow 4)REM sleep 1, 2). The following table summarizes the characteristics and some functions of the four sleep stages:

The frequency * duration of brain waves during sleep explains physiological characteristics and some functions.

During shallow NREM sleep 1 phase, the amplitude of α wave generally decreases, the waveform is irregular, and the frequency can be slightly slower in the later stage, with low amplitude θ wave and β wave, but θ wave is the main one. These two parts together are what we usually call shallow sleep. About 55% people who have slept all night have lost their attention to their surroundings and are unconscious. Heart rate and respiration begin to decrease, and peripheral vasodilation will increase by 30-40%. In a warm environment, the sweating rate in the light sleep stage will greatly increase. In the shallow sleep stage, the muscle tension of the whole body decreases and there is almost no eye movement. Light sleep is a necessary stage from waking to deep sleep, and it is also a necessary stage between deep sleep and REM sleep.

On the basis of low amplitude brain waves, a "spindle wave" with a period of 100-300ms and an amplitude of 100-300μV appears in the second stage of shallow NREM sleep.

There are moderate or high amplitude δ waves in deep NREM sleep. With the further increase of sleep depth, the amplitude will further increase, the frequency will be slow and irregular, and the proportion of δ wave will exceed.

Over 50%

About 15-20% of the whole night's sleep. At this time, the heart rate and breathing will be further reduced, the cerebral blood flow will be reduced, and people will not wake up easily. Brain waves during deep sleep will cause cerebrospinal fluid vibration and wash away brain metabolic waste. The pituitary gland secretes a lot of growth hormone to repair the body. The explicit memory dependent on hippocampus was consolidated.

REM sleep is similar to the awakening period, showing low-amplitude mixed frequency waves and intermittent θ waves, and the eye electrical activity is significantly enhanced during REM sleep. About 25% of the whole night's sleep, the brain is active, the heart rate is accelerated, the myoelectric activity is obviously reduced or even disappeared, and the limbs are like paralysis. Dreams increase at this stage. The secretion of stress-related hormones decreased and negative emotions subsided, which was independent of the consolidation of implicit memory in Haima area.

Second, the sleep cycle and sleep structure

Every night, we go from waking to shallow sleep N 1, and then don't go up the stairs, like N2 shallow sleep, N3 deep sleep, and finally REM sleep until we wake up in the morning. The four sleep stages are roughly according to the combination of shallow-deep-shallow-rapid eye movement-shallow-deep-shallow-rapid eye movement-shallow. The average ............................................................................................................................... is about 90 minutes per cycle (from one REM cycle to the next). If you sleep for 8 hours all night, there are about 5 cycles on average. The sleep structure diagram of the whole night actually depicts the progress of sleep stages and cycles. The simplified version of the whole night sleep cycle is as follows: (Only the red box part is deep sleep)

Although this sleep chart is a simplified version, some people can really sleep out this standard cycle as a teaching material, especially healthy young people! Generally speaking, from the awakening state, you first enter the shallow sleep stage of N 1, lasting about 3-7 minutes, then enter the shallow sleep stage of N2, lasting about 10-25 minutes, and then you will enter the deep sleep stage of N3. N3 may last only a few minutes or an hour. After deep sleep, sleep returned to N2 or N 1 light sleep. Next, enter the first REM sleep and complete the first sleep cycle. REM sleep in the first sleep cycle usually lasts for a short time, about 5- 10 minutes. Then it goes on like this. After midnight, N3' s deep sleep is greatly reduced, while REM sleep is increased. For infants and the elderly, it does not conform to this law.

No matter what stage of sleep we are in, we can go straight into the state of awakening (it would be terrible if we can't wake up), but we can't skip shallow sleep and go straight into deep sleep or REM sleep. Only when normal sleep is resumed after sleep deprivation or deep sleep deprivation will N3 deep sleep come earlier and last longer than normal. Therefore, the long duration of deep sleep can only be said to be an accidental phenomenon and should not be the norm. Of course, too little deep sleep, such as only ten minutes or half an hour, is also a concern, which may imply other health risks.

We all know that deep sleep is good. At this stage, the secretion of growth hormone increases, which can promote the synthesis of collagen, repair our bones and muscles and make our skin and hair beautiful. At the same time, it can consolidate memory and keep the brain healthy. So what should I do to increase deep sleep? In fact, we can't control deep sleep. What we can do is to ensure adequate sleep time, regular work and rest, relax before going to bed, do more outdoor activities ... After all, as long as we live according to the most basic health knowledge, sleep health will naturally happen.

Appendix 1: introduction of five kinds of EEG

According to the different frequency and amplitude of EEG, there are five main rhythms of brain activity, namely:

δ (δ) rhythm: the frequency range is about 0.5~3.5Hz, and the amplitude is about 100~200uV, mainly in temporal lobe and occipital lobe. Delta rhythm mainly appears in deep sleep or coma.

θ (θ) rhythm: the frequency range is about 4~7Hz, and the amplitude is about 50~ 100μV, mostly in temporal lobe and parietal lobe. Theta rhythm mainly appears in the shallow sleep stage (NREM sleep stage 2).

α (α) rhythm: The frequency range is about 8~ 13Hz, and the amplitude is about 30~50μV, which is more obvious in the occipital lobe. Alpha rhythm appears when adults close their eyes and relax.

β (β) rhythm: the frequency range is about 13~30Hz, and the amplitude is about 30V, especially in frontal lobe and parietal lobe. Beta rhythm mainly appears in the active state of brain activities such as active thinking.

Gamma (γ) rhythm: frequency range >; 30Hz, no specific amplitude range. Gamma rhythm may be related to consciousness and perception, that is, related concepts are formed by connecting input information from different brain regions.

References:

1. Sleep Medicine, edited by Zhao Zhongxin, People's Health Publishing House 20161-18.

2.s？ Deep sleep drives brain fluid oscillation.