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Nature of sleep

The true nature of sleep has not been completely understood yet, and probably will remain a mystery forever. Nonetheless, there have been many interesting discoveries and scientific findings on sleep. Here, we try to explain a few interesting facts about sleep without going into too much detail.











Being asleep

Generally speaking, sleep is a state which is in contrast with wakefulness. When you are awake, you can respond more efficiently to external stimuli. When trying to define being asleep, one thing that comes handy is the lack of goal-directed behaviour (in contrast to when we are awake). Being asleep is generally thought of as a state in which the skeletal muscles relax. However, phenomena such as sleepwalking bring some interesting points to the table. Scientists found that during sleepwalking, a portion of the brain is completely awake. This is why a sleepwalker can perform certain tasks that you are not usually capable of when you are fully asleep.

Sleep in animals

In order to find out if other animals sleep in the same way as human beings, scientists use electroencephalogram (EEG) which records brain activities in terms of electrical signals. It has been shown that all human beings have more or less the same EEG pattern while sleeping. Furthermore, this pattern can be used to differentiate if a person is sleeping or not. Similarly, most mammals and birds show more or less the same EEG pattern while sleeping. However, lizards, snakes, reptiles, fishes and insects do no show the same pattern. This makes it more difficult to scientifically differentiate their "sleep" vs awake time. This suggests that the sleep state in some animals might be closer to wakefulness.













Amount of sleep

Adults typically sleep anywhere between six to nine hours per night. However, over the last few decades, in modern societies, the number of people who get less than six hours of sleep has increased drastically. On a separate note, age has a high correlation with the amount of sleep one should get. For example, on average, an infant spends 16 hours a day sleeping. As he/she ages, this number starts dropping sharply.





Sleep phases

Our dreams are clearly influenced by what we do during the day. Our brain is complex enough to divide the night into two phases and process our memories in different ways during these phases. One of these phases is called slow wave sleep (SWS) and the other one is called rapid eye movement (REM). We generally dream during both these phases; but, the nature of our dreams is not the same.







sleep phases





Dreams and our sleep

We saved the best for last. Our dreams are very interesting in nature. Most things we learn during the day are stored in a structure called hippocampus. While we are in SWS, hippocampus starts showing movies to our frontal cortex with a very high speed. In general, these are emotionally charged dreams that are tied to our old memories. Scary nightmares, such as getting buried alive or a beast sitting on your chest, generally happen during this phase. After this, our hippocampus shuts down and we transition to REM. This allows our frontal cortex to process the information. In contrast to SWS, the processing of this information does not happen in a faster or slower pace and that is why REM feels more real. During this phase, our cortex is trying to filter the useless memories out.













One interesting fact about our dreams is that the objects and people are familiar. In our dreams, we typically do not see people that we absolutely do not know. Events that are happening in our lives are the building blocks of our dreams. However, our creativity can play an important role in mixing them up. Moreover, there are studies that suggest our dreams evolve along with our other cognitive developmental processes as we grow up. This one might come as a surprise to you. There have been studies that looked at the quality of sleep in couples. For women, sharing a bed with a partner shown to have a negative impact on the quality of their sleep. However, if there was a sexual contact prior to sleep, this mitigated the negative subjective results without changing the objective ones (balance of SWS and REM was still abnormal though). Nonetheless, for men, the quality of sleep was not affected by the presence of a partner.









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