Even when we sleep our brains are still engaged – organizing our day, putting things into long-term memory, tying up loose ends and taking care of our life as we get our rest. When you are at rest your brain is not.
Scientists first recorded brain activity, through the use of an electro encephalogram recording (EEG), of sleeping subjects they were surprised to find the brain did not rest, but actually worked at lower frequencies than while awake. They called this occurrence “slow-wave sleep,†or “synchronized state,†because there seemed to be a pattern to the frequency.
After the subject is asleep for around 90 minutes the brain does freeze, referred to as “desynchronized state.†During this phase scientists refer to it as the REM state of sleep (rapid eye movement). It is during this time most of our dreaming occurs, and memory consolidation occurs. We usually have 4-5 REM states a night, lasting approximately 90-120 minutes each, with each state slightly longer than the previous one.
Without these slow and then “desynchronized†states of sleep that our brain is able to burn memory – moving it from short-term to long-term. This is why a good night’s sleep is so important. It improves results on memory tests!
It may be surprising to you to know; when you apply electric current to your forehead at the frequency of slow-wave oscillation (1 Hz) your performance on some memory tasks improves – especially when asked to answer “fact-type†questions.
An interesting study was conducted in 2006 at Germany’s University of Lubeck by researchers Marshall, Helgadottir, Molle and Born involving 13 medical students. The students were asked to remember the English translation of some German words immediately before going to sleep. During the slow-wave stage the researchers induced oscillating currents to the foreheads of some of the students. The next morning the students were asked to remember the words learned the previous day. Those who had the currents applied remembered more than those who did not.
The researchers then tried the same experiment on the students during REM sleep and found no improvement at all. There was no improvement noted when applying different frequencies (5 Hz, for example) during slow-wave sleep either.
What this experiment indicates is that the brain produces distinctive brain frequency patterns for different functions, like memorizing. It also shows a definitive answer to the way our brains consolidate memory.
This study is extremely interesting and answers several questions as to how the brain performs during sleep to form long-term memory. I just hope someone doesn’t try to improve their memory by cranking up the amps and applying them to their forehead. They will get more than a memory jolt.
From the desk of Ron White
Sources:
The Sleeping Brain (some in research) – Rolling Waves and Arctic Icecaps in the Sleeping Brain: Oscillation States Switch, by Chengyu Li, Ph.D
http://brainconnection.positscience.com/content/312_1