What is the Deepest Stage of Sleep?

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As I tossed and turned last night, I started to wonder what is the deepest stage of sleep I get at night? Sometimes the slightest noise can wake me up, but I will sleep through rumbling thunder. I woke my girlfriend up at around 3:39 am this morning to ask her, which was met with aggression. So to save anyone here the hassle, I got your answer.

The deepest stage of sleep is REM Stage 4. Usually around 90 minutes after being asleep, your body enters the rapid eye movement stage, or REM, that usually lasts around 10 minutes. During this phase of sleep, that sleepwalking, bed-wetting and the most powerful dreams occur in this state.

That is the short answer, however, lets dive deeper into what this stage of sleep is and how it affects your sleep.

What Happens at the Deepest Stage of Sleep?

During REM (Rapid Eye Movement) sleep, the first thing you will notice is, as the name implies, the rapid eye movement. Your eyes will rapidly move in all directions while your eyelid is closed. During this phase of sleep, it is reported that sleepwalking, bed-wetting and the most powerful dreams occur in this state.

Ever have one of those dreams where something happens and it wakes you up? You probably have a vivid memory of this event for the next few minutes, but this usually happens in REM sleep. REM sleep can get longer and longer as you sleep and can last up to an hour as the night continues. During REM, you can also experience increased respiration and heart rates during your sleep.

Why Do We Have REM Sleep?

The science is out on the exact reason why we enter into this type of sleep, and what benefits it offers us during this time. It is estimated about 25%, or two hours, of your total sleep time is spent in REM. We do know from brain scans of patients in REM, that the brain is highly active during this time.

UCLA did a study back in 2015 that was posted in Nature Connections and suggested that our brain is switching to a different type of mental imagery, which could account for why our eyes move randomly during REM sleep.

But WHY do we have REM sleep?

It is theorized that during REM sleep, the brain is processing memories, storing information and balancing your mood. Since the EXACT reason we enter REM sleep is not known, what exactly is going on is still not understood.

What We Do Know About REM Sleep

Different parts of the brain light up right before we enter REM sleep and it begins in response to the signals sent from different areas of the brain. The cerebral cortex, which is what takes care of things like thinking, learning from your environment and centralizing information, get the signals from your brain and shuts down movement from the neck down. This creates a temporary paralysis to prevent you from moving or damaging yourself during REM sleep.

Ever had a dream that snapped you awake? Get hit with something in a dream that woke you up and you could swear you actually felt it? This is a disruption of those signals and your brain alerting you to danger that wakes you out of this state. Your body’s natural defenses to threats that should have been turned off during REM.

While your brain is in this state, the parts of it responsible for learning are also stimulated. Studies show that when people are not allowed to enter into REM sleep, they are unable to remember things they were taught before they went to sleep. This study was done by the National Institute of Neurological Disorders and Stroke in 2007.

How Important is REM Sleep?

Apparently very important. As the brain uses this time to process memories and store learning experiences, well, we think it does anyway. Most mammals and birds also show signs of REM sleep as well. Sigmund Freud believed that dreaming during REM was a “safety valve” for you unconscious desires. It was not until after 1953 the scientists found REM in sleeping infants and took serious notice with sleep, REM and dreaming.

Today, scientists believe that your brain uses this time to interpret, organize and categorize your memories. Events and activities of the most recent few days to store the important memories for you to remember. Not everything we see and do every day is important to be saved.

As a quick example, think of a food that you really do not like. I am sure you can remember the taste and when you tried it last. Can you remember what time of the day it was? How about the weather outside? How about the day of the week it was? You can now see that not everything you experience is worthy of remembering. This is what scientists think what happens during REM sleep. This is your brains time to “clean up” your memories.