Sometimes, we think of sleep as waste of our time, preferring to study all night before an exam instead of sleeping. No, it is the worst thing you can do to yourself and to your brain.
Did you know that during the day you accumulate toxins in your brain? No? I was shocked when I discovered it too, but it is true.
Jon Hamilton (2013) explains that when you (or your pet) sleeps, your brain "cleans" itself and reduces or gets rid of harmful substances that are present. These substances are mainly responsible for diseases, nasty conditions and cognitive difficulties, like Alzeimer's, headaches, the famous "blank" moment in your exam, an impaired immune system between many others (same example are exposed on the figure below).
Imagine your brain full of poison, do you think it can work properly? Correct, the answer is NO. You will not be able to think clearly about what you studied. So, if I sleep properly just the day before my exam is it enough? hum, to answer this question I will ask another for you to think about: If you eat fast food, artificial products, no fruits, no vegetables during months, years, and one day you resolve by eating healthy food, is it enough to make your body healthy? You know the answer.
Sleep affects your memory and learning too. How? One manner I mentioned before, without toxins you can think clearly. But have more.
During your proccess of learning you study many ideas and concepts. Between them, there are key things you need to consolidate in your brain. While you sleep, your brain works. It develops new sinapses, cleans the less important ideas and strengthens the more important ones.
In the moment of your repose, your brain is in deactivation. That moment the pre-cortex works hard to understand and put together knowledge. If you study before a nap or a night's sleep, you have a better chance of dreaming what you were studying or connect important areas to consolidate your learning.
I am sure you have heard of reports from people (maybe even you) who were trying to sort out a problem, it was hard, so they went to bed to sleep thinking of trying again the next day and during their sleep, they dreamt of the problem and found the solution. It happened with Mendeleiv and the Periodic Table, how related in "A História da Tabela Periódica" (The History of periodic Table):
"Overcome by the tiredness, he fell asleep on the studies' table and had a dream. -- I saw in a dream a table that every element was fit perfectly. When I woke up, I wrote immediately on a sheet of paper -- related Mendeleiv after."
So, learning during sleep is possible!! Sleep ENOUGH and learn more.
Video Lecture by Barb Oakley: 1-7 The importance of sleep in learning. Learning How To Learn. Coursera. https://class.coursera.org/learning-001
John Hamilton. (October 17, 2013). "Brains Sweep Themselves Clean of Toxins During Sleep." NPR All Things Considered.