In Texas, the schools have been in session for two weeks now, and you can see the fatigue starting to set in. The initial excitement of being back in school has worn off. In the mornings, school parking lots are full of students with tired stares who are still getting used to getting up early for school. So, how important is it to get a good night's sleep? What is sleep doing for us, after all?

It is strange that we don't know more about what happens to the body and brain during sleep. After all, we spend about a third of our lives asleep. Think about it, by the time you turn 30, you have spent about 10 years of your life asleep.

A review paper in the September, 2009 issue of Psychological Bulletin by Matthew Walker and Els van der Helm discusses some influences of sleep on . They point out that there are a two key stages to learning new information. First, there is the period in which you are exposed to the information. Psychologists call that encoding. Then, there is the period after you have been exposed to the information in which the information has to be locked into memory by affecting the connections between neurons in your brain. This process of locking in the memory is called consolidation.

It turns out that sleep matters a lot for both aspects of memory.

Sleep deprivation (and particularly deprivation of a particular stage of sleep called or sleep) affects brain circuits that make it harder to remember new things. It has a particularly big effect on information that is emotionally positive or neutral. Because many things learned in school are emotionally positive or at least not negative, that means that lack of sleep can have a particularly large effect on information learned in school.

Sleep also affects the consolidation of memories. There are a few influences that sleep has on this consolidation process. First, quite a bit of memory consolidation happens during sleep, so disrupting sleep will make it harder for memories to be retained for the long term. Second, sleep helps to separate the emotional component of a memory from the other content of a memory. So, if a student has a bad interaction with a teacher or friend during the day, sleep will help make the memory feel less negative the next day.

Now, the way many people try to deal with a lack of sleep is to drink something with (like coffee, soda, or Red Bull). Caffeine does "wake you up." But it does not seem to revive the brain circuits involved in helping you to form memories. Unfortunately, then, there is no liquid substitute for getting a good night's sleep. In the end, you need to sleep both to be prepared to learn new things and to make sure that the things you learn get locked into your brain.