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Most people know the advice "sleep on it" as a piece of folk wisdom, something to say to a friend who cannot decide. Yet research on sleep over the past few decades suggests that this advice may be more scientific than it sounds. While you rest, your brain is far from idle: it is sorting, strengthening, and storing what you learned during the day.
The process is known as memory consolidation, and it is linked to the different stages of sleep. During slow-wave sleep, the deepest stage of non-REM sleep, the hippocampus, a region of the brain involved in forming new memories, appears to replay recent experiences. These memories are then gradually transferred to the neocortex, where they can be stored for the long term. In simple terms, what you learned in the morning becomes more stable during the night.
REM sleep, the stage in which vivid dreams are most common, seems to play a different role. Studies suggest that it is more closely associated with procedural memory, such as learning a skill like playing an instrument, and with the emotional side of memories. Some researchers also believe that REM sleep helps the brain to connect new information with what it already knows, which may be important for understanding and creativity.
The other side of the coin is what happens when sleep is cut short. Sleep deprivation has been shown to impair learning in two ways. First, a person who is tired cannot concentrate properly, so the information is not absorbed well in the first place. Second, without enough sleep afterwards, the consolidation process is disturbed, and new memories may be weaker or may be lost more easily.
This has practical implications. Students who stay awake all night to study before an exam may be working against themselves, since the hours they save may cost them what they have just learned. A better strategy is to study, review briefly before going to bed, and sleep well. Of course, scientists are still debating many details, and the effects vary from person to person.
So the next time you are tempted to sacrifice an hour of rest for one more hour of study, it may be worth asking yourself a simple question. Who is doing the real work of learning: the hour you spend awake, or the night that follows?
