It has been known for some time that we process memories and experiences during our sleep. However, it is new that our brains selectively process memories during sleep. The latter fact is the conclusion that emerged from research conducted by researchers at the UMC St. Radboud.
The importance of sleep
There are still many discussions going on about the function of sleep. What has been proven is that people who are sleep deprived have difficulty concentrating, are mentally tired, have a longer reaction time and are forgetful. There have even been extreme cases where people have started hallucinating and even died from sleep deprivation.
Sleep stages
The time we sleep is divided into different phases:
Phase 1: falling asleep
This phase only lasts a few minutes and during those minutes you slowly fall asleep. Your body temperature drops, your heart rate slows and your breathing becomes calmer. You may wake up with a start because you felt like you were falling. This is because the muscles of your arms and legs tighten completely for a short time. The name for this is a sleeping convulsion.
Phase 2: light sleep
In this phase you really start to sleep. You still wake up easily from strange sounds or other observations, but your body relaxes more and more. This sleep phase lasts between 30 and 40 minutes and you spend about 50% of your sleep time in this phase.
Phase 3: transition phase
The third sleep phase is a transition phase from light sleep to deep sleep. In this phase, your breathing becomes more regular, your heart rate drops further and your muscles relax even more.
Phase 4: deep sleep
In this phase your breathing is the slowest, your heart rate is the slowest and your muscles are completely relaxed. In this part of sleep, growth hormones are released and your body recovers. This phase also plays a role in processing experiences.In this phase you have difficulty waking up and when you wake up you are confused and drowsy. This phase lasts longest at the beginning of the night and becomes shorter with each cycle.
Phase 5: REM sleep (Rapid Eye Movement)
This is the phase in which you dream. Your muscles are completely relaxed, so you don’t actually perform the movements of your dreams. During this sleep phase, blood pressure rises, your eyes move quickly back and forth and your brain is very active. The theory is that you process experiences and memories in this phase.After this phase, which takes up about 25% of your sleep time, you unconsciously wake up and start a new sleep cycle.
Process memories selectively
During the research at the UMC St. Radboud, two groups of test subjects were used:
- A group that had to remember the location of photos with buildings and furniture on them in the morning. After learning, some participants were told that they would only be tested on the location of the photos with the furniture. Others were told they would only be tested at the building site. This group then simply went to work or school and returned in the evening to undergo the test.
- The other group had to learn the locations of the photos at night and then simply went to sleep at home and performed the test in the morning. Also in this group, some were told immediately after learning that it was about the furniture and others that it was about the buildings.
After exactly 14 hours, the participants took the test. Just before the test, the participants were told that this concerned all locations. The results:
- The people who went to sleep were able to remember more locations from the category they had first been told was most important than from locations that were not important.
- The people who started carrying out their daytime activities knew fewer locations from the important category than from the non-important category.
Sleep apparently ensures that specific memories are retained longer. Moreover, the experiences selected by the brain are easy to influence . For the participants, a simple instruction after learning was sufficient to create the differences. Follow-up research could clarify how sleep can be used to improve study results.