Why do we sleep?
About one third of our lives is spent with sleep. What a waste, it seems. But nature is smarter than human beings. If sleep is not necessary the evolution would have eliminated the need for sleep. Several animal experiments have shown that sleep is vital. If sleep is suppressed for a prolonged period of time we most likely will die. We do not exactly know, why we have to sleep. But today we have accumulated a large body of scientific evidence about various structures in the brain which play an important role in sleep and wakefulness.
Sleep can be made visible. Thanks to the invention of Hans Berger the electrical activity of the brain can be measured. Depending on the specific brain wave pattern sleep or wakefulness can be visualized. This is the basic investigation that can be performed in a sleep lab. It is called polysomnography.
During sleep the brain is active
Not too long ago it was thought that sleep is a deathlike state. Thanks to the invention of Hans Berger we know that the brain is highly active when we sleep. Sometimes certain brain regions during sleep are as active as during wakefulness. Other body systems such as the immune system and certain hormone systems are more active during sleep that during wakefulness.
It was also believed that the sleeping individual could not perceive the environment. But now we know that the sleeper can receive information from the surrounding environment and sort them by relevance. One good example is the ability of sleeping new mothers who are able to ignore loud noises from a truck but swiftly react to silent requests of their newborns.