Sleep is an essential daily activity that we automatically partake in and rarely give a second thought. We know that we need a good night's sleep in order to function properly the next day and that if we sleep poorly, our mental capabilities are reduced, and we feel tired. It is as important to our health and survival as eating and drinking, and yet why we need sleep is still somewhat a mystery and continues to baffle scientists. However, as science has developed, we are now understanding more about the purpose of sleep and what happens in our brain.
Why do we need sleep?
Most adults require between seven and nine hours' sleep a day in order to stay healthy and function at optimal capacity. Sleep allows our cells to repair and regrow, helping the brain restore itself so that we wake up feeling refreshed and energized. We may think that during sleep our brain “switches off,” when in fact our brains are working hard to store new information from the day, process memories and get rid of toxic waste.
We’ve all experienced the effects of sleep deprivation at some point in our lives and may be familiar with the exhausted-walking-zombie feeling. A lack of sleep not only makes us feel sleepy, but can also impact many aspects of brain function including learning, memory, problem-solving, creativity, decision making, focus and concentration.
How does sleep affect the brain?
There are four main stages to sleep. The first three are deep, non-rapid eye movement (REM) sleep and the fourth one is light, REM sleep — where dreams occur.
According to a 2017 study published in Nature Communications, a restless deep sleep may reduce the brain’s ability to learn and store new information. Throughout the day, information we obtain is passed between neurons in the brain via connections called synapses. When we learn new information or skills, new synapses are formed. That lightbulb moment when you suddenly understand something is really just the formation of these synapses. The brain’s ability to rewire itself in this way is known as neuroplasticity, which is crucial for learning new skills. During sleep, these synapses become inactive and without this restorative period, the brain’s neuroplasticity is weakened.
A recent study reveals that REM and non-REM sleep work together to increase learning capability. REM sleep strengthens new synapse connections between neurons, to prevent them getting erased by subsequent learning. Practice makes perfect - whilst you sleep soundly, your brain is making sure you remember those important things you learnt the day before. The amygdala, a small almond shaped structure in the brain involved in processing emotions also becomes very active during REM sleep, which helps us extract meaning from what we have learnt.
However, further research suggests sleep is just as important for forgetting information, as it is for learning new information. The brain stores information and memories for a short amount of time whilst it processes them and decides what is important and needs to be stored as long-term memory. It is thought that during deep sleep, the brain discards information deemed as unimportant or suppresses memories to allow it to have space to obtain new information without becoming overwhelmed.
Additionally, it is currently believed that our brain performs housekeeping whilst we sleep by removing toxic proteins from the brain. These toxic proteins build up throughout the day and can impair the flow of information between neurons. These toxins can also cause harm to brain tissue and memory function and lead to neurodegenerative diseases such as Alzheimer’s.
Sleep may have anti-anxiety and pain-relieving affects on the brain - you may be familiar with the sour mood following a poor night’s sleep. Research suggests an area of the brain associated with pain sensitivity becomes hyperactive after a bad night's sleep. Activity is simultaneously reduced in the area of the brain responsible for releasing dopamine, a hormone which makes you feel pleasure.
In order to live a healthy, happy life, a good night’s sleep is essential. If you experience sleep deprivation, your brain may not be functioning as well as it could be, and by simply improving your length or quality of sleep, you could unlock a whole new you.
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