Sleep plays a huge part in our lives. If we don't get enough sleep, we feel groggy and irritable. But did you know that sleep affects our memory and our learning too? Many studies have shown that not only the quantity of sleep, but the quality of sleep affects learning and memory.
Biologists study sleep and the part it plays in learning new skills in two different ways. Firstly, they look at the different stages of sleep and how this affects the brain taking in and retaining new information. The second study is how sleep deprivation affects the brain when learning new skills and remembering them.
First things first, let's take a look at what a memory is.
There are 3 different types of memories.
- Fact- based e.g., remembering the capital city of the UK.
- Episodic e.g., an event in your life (getting married)
- Instructional e.g., how to drive a car or how to play an instrument.
For any of the above acts to become a memory, there are 3 things that need to happen.
- Acquisition - experiencing or learning something new
- Consolidation - the thought becoming a memory in the brain
- Recall - being able to access the memory in the future
Acquisition and recall happen when we are awake, and consolidation happens when we are asleep. Scientists believe that consolidation needs to happen whatever the memory type (fact based, episodic, instructional) and can only happen when you are asleep. This is called the consolidation theory by biologists. The consolidation theory is the theory in which your brain has to sleep in order for your learnt skills to be held in your brain to become a memory for you to access.
Next, let's take a look at the different stages of sleep:
Awake (No Rapid Eye Movement):
- Before you fall asleep
- When you first wake up
- Brief moments during sleep. These moments can be so quick you don't remember that you even woke up.
Light sleep (NREM):
- Muscles are relaxed but might jerk and jolt
- Respiration and heart rate slows
- Body temperature drops
- It is easier to wake up if you are in this sleep stage
Deep sleep (NREM):
- Blood pressure drops
- Blood flow increases to muscles
- Growth hormones are released
- Tissue growth and cell repair starts
- Long and slow brain waves
- Waking up is hard - you can feel groggy when woken
REM (Rapid Eye Movement):
- Respiration and heart rate increases
- Vivid dreams can occur
- Temporary paralysis - except for eyes and breathing muscles
- Memory, learning and problem-solving are being processed
- Eyes move rapidly (hence the name)
- Brain activity is almost the same as when we are awake
How do things we have learnt turn into memories?
If you have a healthy sleep pattern it is likely you will go through all of these sleep stages at some point. Typically, you would experience REM sleep during the later hours of your sleep. This explains why sometimes we have extremely vivid dreams right before waking up. Many believe that the REM stages of sleep are crucial for things like memories and learning and is when the consolidation theory takes place.
Short-term memories are created in the hippocampus and neocortex part of the brain. Scientists think that the hippocampus replays the events of the day and then the neocortex reviews and processes the memories. During the review, the neocortex will decide if the memories and skills of the day are worth keeping. Anything that is deemed as important will be sent to the cerebral cortex to be kept and turned into long-term memories. This could explain the vivid dreams during the REM stage.
Other scientists think that this process happens during the NREM stages of sleep too. It is thought that the NREM stages prepare the brain for learning new things the next day. Then as you transition into REM sleep, the hippocampus and neocortex work their magic. This is something that has divided scientists for many years. However, scientists have now come to the conclusion that it is likely that this process of storing memories happens during all stages of sleep. Perhaps the process needs all stages of sleep to be completed.
What happens if you don't get enough sleep?
Sleep is incredibly important for our health. If we don't get enough sleep our physical and mental health really does take a beating. Studies have shown that when we don't get enough sleep, we find it hard to concentrate, we work slower, and careless errors can be made. When we are over-tired, we can microsleep. This is when the brain waves slow down as if you are asleep when in fact you are awake. If you've ever 'spaced out' before, this is what is happening in your brain. Many huge disasters have happened because of over tiredness and microsleeping.
According to scientists, when we are tired, our learning abilities decrease by 40%! The University of Cambridge in the UK often asks volunteers to come into the science labs and perform a mathematical task. They choose maths because it requires problem-solving and learnt skills (memories). They first perform this task when they are not tired. The scientists use brain imagers to take a look at what happens in the brain when they are busy solving the task. They notice that the front of the brain, the thalamus, has lots of blood rushing there. This is because this part of the brain is where most of the memories are stored. When parts of the brain are being used, oxygenated blood is rushed to the neurons in that area, Neurons need oxygenated blood to function properly. They then ask their volunteers to stay awake for either 24 hours or 48 hours and then get them to repeat the mathematical process. The scientists learn that only a small amount of oxygenated blood rushed to the front of the brain. They also notice that generally, there is not a lot of oxygenated blood around the brain. This is why it is believed that when we are tired, we cannot focus. There is a lack of oxygenated blood going to the brain.
Chronic tiredness and memory
As well as learning errors, people who are persistently sleep-deprived are likely to have high blood pressure, diabetes or narrow blood vessels. All these conditions decrease blood flow to the brain. Scientists have also looked at the possibility of persistent sleep deprivation and dementia. Biologists had 2 groups of mice. Group A were not allowed to rest and sleep. Group B were allowed to do so. After a period of time, they ran some tests on the mice who were not allowed any sleep. They discovered that the mice had developed proteins called beta amyloid in their brains. Group B did not develop this protein. In humans, beta amyloid in the brain is known to make memory and learning skills decline. Often people with lots of beta amyloid proteins in their brain, will have been diagnosed with dementia. Because of this, scientists believe that there is a direct link between lack of good sleep and dementia. Not only does persistent lack of sleep cause short-term problems but can cause long-term problems too!
In conclusion, sleep is a vital part of our mental and physical health and wellbeing. It gives us the ability to take on new challenges, learn exciting new things and remember special moments in our lives. It is recommended that adults get around 7-9 hours of sleep a night. Of course, this isn't always possible, but this should be the goal. If you are struggling to sleep or feel like you aren't getting a good quality sleep, you should contact your doctor for sleep advice and help.