Sleep

We spend about one-third of our life sleeping. It is a normal body process that allows our body and brain to rest. For most people, it’s just a matter of getting comfortable, closing your eyes and drifting into slumber. So, sleep looks deceptively simple. But despite how simple it seems, sleep is one of the most complex and mysterious body processes known to science. Even Researchers and experts struggle understanding it because of the mysteries surrounding how and why we sleep and what happens to us while we sleep.

Before the 1950s, most people believed sleep was a passive activity during which the body and brain were dormant. But subsequent studies have revealed that sleep is a period during which the brain is engaged in a number of activities necessary to life. Hence, sleep is essential for life and not an overhead.

Your body cycles between being awake and asleep throughout each day, with certain processes only happening when you’re asleep. When you’re asleep, your body “powers down” and most body systems — including your brain — become less active.

Some of the key things that happen while you’re asleep include:

• Energy conservation and replenishment. While you’re asleep, your body uses less energy. That lets body cells conserve energy and stock up for the next day.

• Self Healing and Repair. Being less active makes it easier for your body to heal injuries and repair issues that happened while you were awake.

• Memory Consolidation - While you’re asleep, your brain does a memory consolidation – linking information received while awake in the form of short term memories, with previous experiences and puts the important and useful information into long term memories. And, discards the trivial short term experiences.

Sleep Cycle

You may not know it, but while you're asleep on a night, you're going through multiple sleep cycles. And, in each sleep cycle, you're going through four sleep stages.

Stage 1 (N1) Light Sleep

Lasts from 1 to 7 minutes. In this stage you're moving from wakefulness to sleep. Your muscles start to relax. Your eye movement starts to slow down, your heartbeat slows down, and your breathing slows down. As you're sleeping very lightly, it's very easy to wake up during this stage – like due to a small movement, or a light or a sound. If you wake up, you could feel like you just came out of a deep sleep and feeling very groggy.

Stage 2 (N2) Intermediate Sleep

Lasts for about 25 minutes. There is further slowdown of your heartbeat, breathing and eye movements. Your muscles relax further. Your brain activity starts slowing down, as well as your body temperature. The sleep in this stage is deeper than N1 stage, but you are still sleeping somewhat lightly. So, you could wake up quickly if some sound goes off or the lights go on in the room. But if you do wake up during stage two, you shouldn't feel too groggy.

Stage 3 (N3) Deep Sleep

Lasts for 40 minutes. Also known as slow wave sleep. In this stage, your body relaxes even more. Your muscles and bones are recovering and growing – extremely important for athletes and after workout. Your immune system is strengthened. Your breathing and heart rate are very slow. The brain waves show a clear pattern of slowed activity that is markedly different from waking brain activity.

It is believed that deep sleep plays an important role in recuperation of the body as well as effective thinking and memory. It is the deepest part of sleep when it's hard to wake up, even if light goes on in your room or you hear a loud noise. But if you do wake up, you're going to feel very groggy.

Stage 4 REM Sleep

REM stands for Rapid Eye Movement as this is the sleep stage when your eyes are moving behind your eyelids. Also, this is when your body is going into beast mode. Your heartbeat actually increases, blood pressure goes up, breathing increases and becomes more irregular. At the same time, your legs and your arms get paralyzed.

During this time, brain activity picks up significantly, and most of the body — except the eyes and breathing muscles — experience temporary paralysis.

While you can dream in all four stages, your most vivid dreams are going to happen during stage four. So, you don't want to act those out in real life. At the same time, during stage four, a lot of learning is happening. Your memories are being consolidated and indexed, and your mood is also being regulated.

How Sleep Occurs? - Two-Process Model of Sleep & Awake

The sleep-wake cycle is regulated by two separate biological mechanisms commonly referred to as Process S and Process C:

1. Process S (Sleep-wake Homeostasis)

causes a pressure to fall sleep. It is the accumulation of sleep-inducing substances like adenosine in the brain. 

It's really like a balloon which is flat in the morning when you wake up – all sleepiness drained out. As you go throughout the day and use your energy, it gets filled up. And when it reaches a tipping point, you go to sleep and sleepiness again gets drained from the balloon. It effectively reminds the body that it needs to sleep – so the longer you’ve been awake, the stronger your desire for sleep becomes. 

2. Process C (Circadian Rhythm) 

dictates the daily rhythm of sleep.

What is Circadian Rhythm?

Your body needs to follow a schedule because there are many functions that your body needs to perform every single day. But your body cannot perform all of those functions at the same time. And some functions only make sense at specific times.

The Circadian Rhythm is scheduling and optimization of your body functions based on your body’s internal Biological Clock. Our body cells produce their own 24-hour Biological Clock by accumulating and breaking down proteins in a cycle that takes around 24 hours.

The circadian rhythm regulates body’s sleep patterns, feeding patterns, core body temperature, brain wave activity, and hormone production over a 24-hour period. This is what controls the timing of sleep in coordination with the light-dark cycle of day and night. Sleep is promoted by hormone Melatonin, which is naturally produced as light exposure decreases.

These two (process S and process C), work together to create a balanced sleep-wake cycle. While you’re sleeping, the homeostatic sleep drive rapidly dissipates while melatonin is produced as light exposure is reduced. By the early morning, melatonin secretion stops and the circadian alerting system begins. This will overcome the existing sleep drive, thus triggering the body to wake up.  

Even though this model dominates the scientific understanding of sleep regulation, external factors such as work schedules, genetics, food, stress, and exercise also influence sleep times. 

Sleep and Learning

Studies have found that you need sleep after learning to preserve those new memories.

Studies also indicate that you not only need sleep after learning, you also need sleep before learning, to actually prepare your brain, almost like a dry sponge ready to initially soak up new information. Without sleep, the memory circuits of the brain become waterlogged and you can't absorb new information.