It is during sleep when the brain reviews all of the information it received during the day, and either cements it into long term memory or discards it. Until now, the sorting mechanism was a mystery.
Scientists at the University of California San Francisco studied brain waves in rats after teaching them how to use a water spout. During the day, rats practice using a water spout and are rewarding with drinking water. The experiment encompasses all of the ingredients to form a new memory; skill, practice, then reward.
As the rats slept, the researchers tracked two different brain waves that are near the motor cortex, slow oscillation waves, and delta waves. Previous studies linked slow oscillation waves to memory formation, but the purpose of the more abundant delta waves remained a mystery.
Using optogenetics, a technique where researchers control light-sensitive neurons with a laser, the researchers blocked brain waves to see the long term effect. When slow oscillation waves were blocked, rats had a difficult time remembering what they learned about the water spout the previous day — thus confirming the findings of other studies that link slow oscillation waves to memory storage. Interestingly, when the researchers blocked the frequent delta waves, rats were more proficient in recalling the water spout motor skills they learned the day before.
If confirmed, this study clearly shows the function of delta waves is to sort new information into the 'discard' pile of the brain. Next, researchers want to learn more about how the brain decides when the slow oscillation waves or when the delta waves will prevail.
Learning more about this pathway could help develop therapies for recovering stroke patients.