We primarily exist in any one of 2 states at all times, either conscious or unconscious. When we are conscious, our brain tends to work as an on-floor manager who functions around the clock to respond to situations we deal with throughout the day and go through our daily routines. The scenario changes when we go to sleep. Our brain is the night manager now, sorting through the events of the day and tidying up the workspace in the brain. Sometimes it hops onto the couch with some popcorn and turns on its version of the TV: dreams.
Whenever we get tired because we haven’t had enough sleep, it is precisely due to the lack of time our brain has received to clean up the clutter. Our body is also busy as it performs maintenance when we sleep, including tasks such as repairing and regrowing tissues, building bone and muscle, and strengthening the immune system. Our sleep is managed through two internal biological mechanisms- circadian rhythm and homeostasis. The circadian rhythm regulates our body’s functioning throughout the day with the help of our biological clock. It lasts roughly around 24 hours for most people. Meanwhile, homeostasis maintains our body’s equilibrium and tracks our need for sleep. It is the reason why we get increasingly sleepy as our day comes to an end.
Once our body has fallen asleep, we enter non-REM sleep. Our sleep is primarily categorised into rapid eye movement (REM) and non-REM sleep. REM refers to the rapid movement of the eyes back and forth when we are asleep. Despite such sharp movements, the brain is not alerted and no visual signals are sent to the brain. There are 4 stages in our sleep cycles and the first 3 are non-REM.
Another important thing to note at this point would be our brain waves. When we are awake, our brain produces alpha waves. After we fall asleep, our brain waves change frequency and result in different types of waves. Brain waves are recorded using a piece of medical equipment known as an electroencephalogram (EEG).
Stage 1: During this phase, our breathing gradually slows down. The muscles relax and may occasionally twitch in the process. Typically, it lasts 5 to 10 minutes. This is the point where are falling asleep and not quite “there” yet. That is why, people in this stage of sleep do not realise that they were sleeping when awakened. They are also relatively easier to wake up. Brain activity slows down as well and the alpha waves in the brain gradually transform into theta waves. This is also the stage during which we experience hypnic jerks. If you’ve ever suddenly dreamt that you were falling and awoke with a start, you might know what I am talking about. It is not certain why this occurs, although some experts speculate that it might be related to our evolutionary history. Back when man would climb up trees to sleep in the branches, such jerks stopped the muscles from relaxing completely which could result in a nasty fall from the tree.
Stage 2: Significant changes occur during this phase. You are properly asleep now, and the body relaxes completely. Breathing and heart rate becomes regular and eye movements come to a standstill. The body temperature drops and you are on your way to deep sleep. An EEG will record theta waves with brief bursts in between known as sleep spindles. This phase lasts for about 20 minutes and you may sleeptalk.
Stage 3: You have finally entered deep sleep. This is the period when the brain gets to work, decluttering your mental recesses. It is very hard to wake up a person in stage 3 sleep. During this phase, children may sleepwalk. The brain waves fully transition into slow delta waves. Memory consolidation begins as the brain sorts through our memory and organises it properly. The body begins to work on physical repairs and making us ready for the next day. As our blood pressure drops, our body becomes completely still and rests properly
Stage 4 (REM): The 4th stage of sleep and perhaps the most exciting. Before reaching this stage, we cycle through stage 2 once more in a transitory manner. After 90 minutes of falling asleep, we enter REM sleep. Ironically, our brain activity in this phase is very similar to what it would be if we were awake. Along with memory consolidation, our brain also processes emotions. Our eyes move back and forth rapidly as we dream and our muscles are temporarily paralysed to stop us from acting out our dreams. Only those muscles required for respiratory and circulatory functions are kept in motion. Our breathing becomes faster and irregular as we dream and our brain (naturally) gets very busy.
We tend to cycle through these stages a few more times throughout the night. The REM stages which occur later gradually get longer in duration. If a person is unable to sleep for the appropriate length of time, the lack of REM sleep results in an REM rebound. When the person sleeps undisturbed the next time, he/she/they will experience REM sleep for a longer duration than usual. This might be connected to the role it plays concerning learning and memory. Individuals under stress also tend to sleep longer due to the emotional processing and regulation that occurs during the phase.
Sleep has many regulatory functions and benefits as discussed at the start of this article. It is quite necessary to have a good night’s sleep daily. Lack of sleep hampers our normal functioning and may result in an inability to concentrate, crankiness, obesity, a weaker immune system, etc. Unfortunately, many bad habits in the modern world tend to interfere with our natural sleep patterns. Screen time is the biggest culprit as it tricks our brain into thinking that it is still daytime. Most experts recommend stopping using devices an hour before bedtime for this reason.
