The necessity of sleep has always been a bit of an enigma. Although studies have displayed changes in brain function during sleep or the development of brain damage such as schizophrenia after more than 72 hours of sleep deprivation, no one has yet offered a reason why we need as much sleep as we do.
Due to the vast amount of learning that occurs in childhood, baby birds and mammals need almost 3 times as much sleep as their adult versions. Babies have to learn and remember how to move their muscles, how to recognize sounds and repeat them, and how to get meaning from words. It is believed that remembering all these new things requires the creation and consolidation of neural networks during sleep.
Three Stages of Memory Processing
- Stabilization- In this first stage, a memory is being ‘created’ (the science of which is still incredibly unclear). It’s thought to take approximately six hours. A disruption in this process leaves a memory vulnerable to being lost.
- Consolidation- The second stage of memory processing, consolidation most likely involves a combination of glutamate release, protein synthesis, and neural growth and rearrangement.
- Re-consolidation- When the memory is re-activated (i.e. recalled), it is believed that the connections made during consolidation are modified once again. It is the second and third stages that are most dependent on sleep. However, it is important to note that not all memories appear to be reinforced by sleep, and that certain kinds of sleep seem to better support the process of consolidation.
Memories and Sleep
There are two major kinds of memories: declarative or episode memories such as facts versus procedural memories like driving a car. Each is consolidated during a different kind of sleep. Non REM sleep is the dominant form of sleep, occurring just after falling asleep and before waking up. Rapid Eye Movement (REM) sleep occurs later in the cycle, usually only for 20 to 30 minutes at a time, and is characterized by increased brain activity. This is also when dreaming is most common. Research has revealed that procedural memories are consolidated during non REM sleep, and only if sleep is achieved less than 6 hours after the memory is first made. REM sleep, on the other hand, is necessary for consolidation of facts and happenings (like what you ate for breakfast). Without receiving each kind of sleep on a regular basis, memories are weakened, focus is hindered, and the ability to learn and remember new things is impaired.