What happens in our brain when we stay up late?
Go to bed with the lamb, and rise with the lark. Our body is always honest about when to sleep and when to get up. However, if you stay up all night watching football games or struggling with the assignment, your brain is so easily to get dizzy and dazed. That’s the price you should pay for disobeying your body command.
But why should we get sleep? Some people think that sleep helps people to save energy and protect human in wild from being attacked. Some declare that sleep plays an essential role in helping the body to restore itself. Some theories demonstrate that sleep can make room for new knowledge and memory. Additionally, there are also theories say that sleep is an important activity to give the brain a chance to drain out the daily ‘garbage’ that accumulated in our brain. There are numerous different opinions upon why we should get sleep in scientific community. But there is no exact and universal explanation for this question.
However, one thing has been identified by numerous scientific studies: our sleep mechanism is regulated by both the circadian clocks and homeostasis. The circadian clock regulates the timing of periods of sleepiness and wakefulness throughout the day and tells people when to sleep and when to wake up, whereas the homeostasis is responsible for maintaining the balance between sleep and wakefulness – the longer you are in the awakening state, the greater your demand for sleep. As you can imagine, a long time deprivation of sleep is not a good sign. But how bad it is? Recently, a team of researchers from the University of Liege and the University of Surrey have conducted a study to analyse what happens inside the human brain when staying awake for a day, a night and another day before sleep and 33 volunteers in this study had to sacrifice their sleep for science.
The researchers recruited 17 male volunteers and 16 female volunteers around 21 years old. These volunteers voluntarily accepted a ‘cruel’ treatment – during the process of experiment, they were forbidden to go to sleep for 42 hours! And in order to determine which parts of brain are affected by sleep deprivation, they had to undergo 12 times of functional magnetic resonance imaging (fMRI) scan. During each fMRI, they also need to undergo Psychomotor Vigilance Test (PVT) to detect their response at that time.
Fortunately, these volunteers can get a comfortable sleep after this “42 hours’ non-sleep challenge”. After that, they were required to come back and accept the 13th fMRI, and this fMRI data will be compared with the data collected during sleep deprivation. Additionally, the researchers also monitored the participants’ melatonin levels during the entire experiment because the change of melatonin level can reflect the circadian clock cycles. By contrasting data from different periods, the researchers were surprised to find out that the effects of sleep deprivation on different regions of the brain are not consistent. The response of different brain regions to the circadian clock can be divided into two types: strict type and loose type. Some regions under the cerebral cortex, such as midbrain and thalamus are strict type. They were waxed and waned in sync with the circadian clock even if people don’t get enough sleep. But in most areas of the cerebral cortex, such as the prefrontal cortex, the effects of the circadian clock were overridden by the body’s demand for sleep. As long as the sleep demands are high, these regions will automatically enter an inactive state. The researchers concluded that this is why we will feel dizzy in the daytime after staying up for a whole night – how can you ask your brain to response as usual when many regions of your brain have completely disregarded the circadian clock and enter the inactive state?
The change of brain activity by sleep deprivation is also reflected in the behaviours of the participants. As the awake time went by, they became more and more anxious and blue. The results of the PVT also indicated that the sleep deprivation made their response slower than the usual, particularly in the morning. The factor is that the cognitive abilities and emotion of those participants were negatively influenced by the sleep deprivation. After receiving adequate sleep, according to fMRI data, participants’ body indicators returned to the normal level. However, it should be noticed that the tests used in this study are not designed for determining the long-term effects. Therefore, we can’t conclude that spending whole day for sleep can pay the sleep debt caused by two days sleepless.
It is a hard task to keep your mind clear after staying up for a whole night. This study reveals the reason behind this circumstance. Scientist can have a better understanding of the effects of sleep deprivation on different brain regions, which will benefit the study of neurology. And for the public, this study gives an important advice – which we have heard thousands of times: Don’t stay up late unless you need to.