Scientists have been trying to uncover the reason why humans spend as much as one- third of their lives asleep, so far only certain that a lack of it causes many negative health effects.
New research has shown that a lack of sleep can lead to depression, memory loss, and the deterioration of cognitive function, which can significantly affect the way that new learning and development takes place.
Why is sleep important?
In a new study, researchers have proven that sleep helps to reset the build-up of connectivity in the human brain, which occurs during the hours spent awake.
Without this reset, memory and learning are consequentially affected, making it more difficult to adapt to the world around us. Scientists have found that losing just one night of sleep can actually block the brain’s ability to naturally reset, which severely affects learning and memory-building capability thereafter.
Dr. Christoph Nissen, a psychiatrist at the University of Freiburg, led the study and concluded: “Why we sleep is a fundamental question. Why do we spend so much of our lives in this brain state? This work shows us that sleep is a highly active brain process and not a waste of time. It’s required for healthy brain function”.
What exactly needs a reset? 
In 2003, scientists from the University of Wisconsin-Madison concluded a study known as synaptic homeostasis hypothesis (SHY), which explained why our brains need sleep to reset itself for the next day.
It explained that our brains absorb so much information during the day, from climatic conditions to the morning news, to social media catch-ups, to what we’re studying, that they end up being saturated with neural connections. Sleep allows the brain to unwind, consolidate memories, and refresh itself for the next morning.
A sleep-deprived brain also affects the way that memories are built and stored, which can result in blocked experiences and forgotten information. Professor Giulio Tononi from the University of Wisconsin-Madison says that SHY was able to confirm the results from studies previously only conducted on animals, which gave him “elegant and powerful” insight into the importance of sleep in humans.
“Sleep is essential and one main reason is that it allows the brain to learn new things every day while preserving and consolidating memories. Learning and memory require synaptic activity, which is very energetically expensive and prone to saturation. Sleep allows the brain to renormalize this synaptic activity after it increases in the waking day,” he said.
What is therapeutic sleep deprivation?
Dr. Nissen and his team have developed a radical treatment for patients suffering from mental health disorders. Known as “therapeutic sleep deprivation”, Nissen found that depriving people diagnosed with depression with sleep for one night resulted in a 60% improvement in mood, motivation, and cognitive function. “We think it works by shifting these patients into a more favorable state”, he said. 
While therapeutic sleep deprivation has offered some interesting results, many patients relapse after the next night’s rest, which makes it an invalid solution. However, Nissen says that it simply proves that a shift in mood or state is possible within a matter of hours and that sleep itself plays a major role in mental health.
“The idea is that we use sleep and sleep deprivation to understand the brain and develop new treatments. If you think about antidepressants or psychotherapy, it can take weeks or months to see any effects,” he said.
Many scientists and mental health professionals are excited about the findings of these studies, eager to see what ongoing research will bring.
“These new results should strongly motivate further studies in patient groups, both to learn more about the roots of the disorders and how to treat them,” says Professor Westlye from the University of Oslo. “The results could throw light on links between the biology of sleep, more complex brain functions, and severe mental disorders such as schizophrenia and depression.”
Sources:
https://www.biologicalpsychiatryjournal.com/article/0006-3223(91)90255-K/abstract?cc=y=
https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0447.1988.tb05104.x/abstract
https://www.sciencedirect.com/science/article/pii/S0006322312006348
https://www.sciencedirect.com/science/article/pii/S0361923003002594
https://www.sciencedirect.com/science/article/pii/S1087079205000420
https://www.hindawi.com/journals/np/2012/415250/abs/
https://www.annualreviews.org/doi/abs/10.1146/annurev.physiol.63.1.847
