Why do we sleep?

Sleep is one of the heavily debated topics in different scientific fields, as although there is much known, much of it remains a bit of a mystery in some aspects. Sleep has been found to influence many of our waking behaviors. And a lack of sleep can ultimately be fatal.

Sleeping is good for the brain: better memory
There are several theories on why humans and other animals need sleep. In terms of humans, there is the synaptic homeostasis hypothesis. This hypothesis focusses on the synapses in our body, which can be simplified as the connection between two nerve cells. The synapses between these cells enable signals to pass through, thus a message can pass from one nerve cell to another. These synapses play a big role in regards to memory. When we’re awake we constantly receive information about our surroundings, whereas, during sleep, this isn’t the case. Thus during wakefulness synaptic strength increases, and during sleep homeostasis takes place.
Homeostasis is the regulation in our bodies to keep things constant. For instance, the human body ensures that the temperature is about 37°C. This regulation system is also active in synaptic strength, in which sleep is an important factor. The benefits of this are better memory and learning.
Thus to regulate the synaptic system, sleep is needed to downscale the synaptic strength that has been built up during the day. This system is very energy efficient (Tononi, & Cirelli, 2006).

What is REM sleep and why do we need it?
Rapid Eye Movement sleep is a phase of sleep in which the eyes rapidly and randomly move around. What is interesting about this phase is that people are likely to dream during this time. And brain waves during REM are similar to waves associated with being awake. In order to test the function of REM sleep research is often times carried out on animals such as rats. These animals are deprived of REM sleep and, for instance, put in maze studies. And usually, the results indicate that REM sleep is associated with memory (Rasch, & Born, 2013).

Another theory on REM sleep is that it might be related to protoconsciousness. First, there is primary consciousness which is made up of emotions and perception. And there is secondary consciousness, which is related to language. Examples of this form of consciousness are self-awareness, abstract thinking, and metacognition. These two types of consciousness are different in three different stages we go through each day, being awake and being asleep (REM-sleep vs non-REM sleep). The amount of REM sleep peaks while in the womb, and slowly decreases over a lifetime. The possible reason for this peak in the womb could be due to limited external input. REM sleep then helps to build sensorimotor integration without the presence of this input. Sensorimotor integration is important in creating a unified system of neurons. Thus during sleep and dreaming, primary consciousness (protoconsciousness) is present, we move through a virtual world (perception) and experience emotions. Secondary consciousness is experienced while awake or during a lucid dream. Lucid dreaming is when one is aware that he/she is dreaming and in most cases can consciously alter their dreams. Different parts of the brain are active during these two types of consciousness (Hobson, 2009).
Aside from this, homeothermic animals (includes humans) need to get enough sleep in order to maintain weight and body temperature.
Hobson, J. A. (2009). REM sleep and dreaming: towards a theory of protoconsciousness. Nature Reviews Neuroscience, 10(11), 803-813.
Rasch, B., & Born, J. (2013). About sleep’s role in memory. Physiological reviews, 93(2), 681-766.
Tononi, G., & Cirelli, C. (2006). Sleep function and synaptic homeostasis. Sleep medicine reviews, 10(1), 49-62.

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