Most of us will spend about one-third of our lives sleeping. Have you ever considered that sleeping is actually the flip side of being awake and is very much an active state? It turns out that REM brain waves resemble awake brain waves or, as David Eagleman says “just like you’re conscious except you’re not moving.”
REM is the Rapid-Eye Movement portion of sleep when you dream, and accounts for twenty percent of sleep time. According to Eagleman, during REM your “heart rate goes up, respiration speeds up, your body can twitch, there is heightened cerebral activity, and paralysis in the major voluntary muscle groups.”
It turns out that everybody dreams, though not everybody remembers that they dream. Perhaps you have engaged in lucid dreaming, a state where you are aware you are dreaming and are able to then take control of the dream.
All mammals and birds sleep but the duration of that sleep varies considerably. Eagleman says there is “no relationship between sleep time and activity level” and that although sleep is essential, it is “not a special higher order function.” If that’s the case, the question then becomes:
Why do we sleep?
Probably most of us would answer that we sleep to rejuvenate our bodies and minds. Given the title of Eagleman’s talk, Why is Sleeping so Important to Learning?, you may not be so surprised to learn that sleep has other functions. As Eagleman described it:
We sleep to consolidate memories, which in turn consolidates learning.
We also sleep to forget – to take out the trash – to rid our brain of the stuff we do not need. (This is based on Crick and Mitchison’s “reverse learning” hypothesis.) I particularly liked the image evoked by Eagleman’s comment that sleeping is an “offline practice session”.
If sleep is so important to learning, it may be useful to have a quick summary of how we process information. Typically, data gets sent to the hippocampus where it is filtered and then sent off to various parts of the cortex. As Eagleman reminded us, the hippocampus decides what to keep on the basis of relevancy to our goals and frequency of occurrence.
The areas of the brain that appear to be involved in sleep include the hypothalamus and the reticular formation, which is responsible for maintaining our sleep and wake cycle. Most of us have probably seen the impact on ourselves of insufficient sleep. We are more tired the following day, perhaps a bit irritable, and less attentive.
Do you ever have difficulty falling asleep? LeAnn Nickelsen addressed this issue in her session on brain nutrition, and that will provide food for thought in my next post.
For more about why we sleep:
- Slate’s 5-part series Why Do We Sleep?
- Response magazine, Seattle Pacific University: Why Do We Sleep?
- Neuroscience for Kids: Sleep