Sleeping is not as easy as you think, there are five stages we have to run through during a sleep, 1,2,3,4 and REM (Rapid Eye Movements) sleep. Usually the brain will go through stage 1 before REM sleep, with the end of first REM sleep it starts from stage 1 again. An average sleeping cycle takes about 90 to 110 minutes. The first cycle of your sleep is begin with light sleep, then comes to short length of REM sleep, and the longer deep sleep. With each cycle, REM sleep period becomes longer with deep sleep period shorten.
Stage 1 is light sleep where you drift in and out of sleep and can be awakened easily. In this stage, the eyes move slowly and muscle activity slows. During this stage, many people experience sudden muscle contractions preceded by a sensation of falling.
In stage 2, eye movement stops and brain waves become slower with only an occasional burst of rapid brain waves. When a person enters stage 3, extremely slow brain waves called delta waves are interspersed with smaller, faster waves.
In stage 4, the brain produces delta waves almost exclusively. Stages 3 and 4 are referred to as deep sleep or delta sleep, and it is very difficult to wake someone from them. In deep sleep, there is no eye movement or muscle activity. This is when some children experience bedwetting, sleepwalking or night terrors.
In the REM period, breathing becomes more rapid, irregular and shallow, eyes jerk rapidly and limb muscles are temporarily paralyzed. Brain waves during this stage increase to levels experienced when a person is awake. Also, heart rate increases, blood pressure rises, males develop erections and the body loses some of the ability to regulate its temperature. This is the time when most dreams occur, and, if awoken during REM sleep, a person can remember the dreams. Most people experience three to five intervals of REM sleep each night.
You cannot talk about science and researches about sleep without knowing how to track a person's sleep scientifically. There are two common method for researchers to study sleep, one is through Polysomnography, the other is through the movement of the body during the sleep.
Polysomnography is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The polysomnography monitors many body functions including brain (Electroencephalography aka EEG), eye movements (Electrooculography aka EOG), muscle activity orskeletal muscle activation (Electromyography aka EMG) and heart rhythm (Electrocardiography aka ECG) during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions respiratory airflow and respiratory effort indicators were added along with peripheral pulse oximetry.
Yet the problem with polysomnography is that, it usually require the test subject to sleep in an environment which is not their own, therefore it may accurately records all the data during the testing, it does not represent the test subject's sleep cycle or sleep state. All the wiring on the subject may also affect their sleep therefore the results are likely to be skewed.
The other method of tracking sleep is through the body's movement while at sleep. This is also the most common technique that is been used in modern mobile apps or products, they utilize the electronic component called "accelerometer", it monitors any slight movement at night and analyzed the data to calculate the result.
This method is much more common than Polysomnography as the subject can sleep in their own bed in their own room which should make them more comfortable for a better sleep, yet the single data of movement by accelerometer still suffers from accuracy, especially those mobile apps.
Dr. Christopher Winter, Medical Director, Charlottesville Neurology & Sleep Medicine, sleep medicine, neurology specialist, has tested several products, apps, and polysomnography to see if the results from these devices are aligned with each other.
Red indicates wakefulness, black is REM sleep, and blue indicates light (light blue) to deep (darker blue) sleep. The graphic shows the comparison very clear, the devices more or less keep up the data with polysomnography, some are relatively similar to the results polysomnography shows yet some are just far out in comparison. This test allows us to understand that commercial products or app may generate the results for your sleep but they are not always (some are never) going to represent a true story of your own sleep cycles.
As my fmp project is about something that helps people, or rather, reminds people to sleep on time. I think this is a good chance to explore things about this activity we do for about third of our entire life. Sleep is a naturally recurring state of mind characterized by altered consciousness, relatively inhibited sensory activity, inhibition of nearly all voluntary muscles, and reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli, but is more easily reversed than the state of hibernation or of being comatose. Mammalian sleep occurs in repeating periods, in which the body alternates between two highly distinct modes known as non-REM and REM sleep. REM stands for "rapid eye movement" but involves many other aspects including virtual paralysis of the body. During sleep, most systems in an animal are in an anabolic state, building up the immune, nervous, skeletal, and muscular systems. Sleep in non-human animals is observed in mammals, birds, reptiles, amphibians, and fish, and, in some form, in insects and even in simpler animals such as nematodes. The internal circadian clock promotes sleep daily at night in diurnal species (such as humans) and in the day in nocturnal organisms (such as rodents). However, sleep patterns vary widely among animals and among different individual humans. Industrialization and artificial light have substantially altered human sleep habits in the last 100 years.
The science today still unable to answer the question of why do human need to sleep, Some believe that sleep gives the body a chance to recuperate from the day's activities but in reality, the amount of energy saved by sleeping for even eight hours is miniscule - about 50 kCal, the same amount of energy in a piece of toast. And there are some other explanations too yet it is unlikely anyone of then is the single answer but all contribute a bit to the real answer.
It seems like sleep does not really contribute much in anyway that is significant enough, however, sleep deprivation could lead to some serious consequences. If you've ever pulled an all-nighter, you'll be familiar with the following after-effects: grumpiness, grogginess, irritability and forgetfulness. After just one night without sleep, concentration becomes more difficult and attention span shortens considerably.
With continued lack of sufficient sleep, the part of the brain that controls language, memory, planning and sense of time is severely affected, practically shutting down. In fact, 17 hours of sustained wakefulness leads to a decrease in performance equivalent to a blood alcohol level of 0.05% (two glasses of wine). This is the legal drink driving limit in the UK. In the US, more than 200000 car accidents are caused by sleepy drivers, killing people more than drunk-driving. It does not take long before brain and body could feel the result of sleep deprivation.
Sleep deprivation not only has a major impact on cognitive functioning but also on emotional and physical health. Disorders such as sleep apnoea which results in excessive daytime sleepiness have been linked to stress and high blood pressure. Research has also suggested that sleep loss may increase the chance of obesity because chemicals and hormones that play a key role in controlling appetite and weight gain are released during sleep.
