Light Sleep: Do you wake up feeling refreshed?
Sometimes you just don’t wake up feeling refreshed. Why is that? In this article, we will answer: what is light sleep, what are the sleep cycles, what are the benefits of light sleep, how does light sleep work, how does it affect the brain and what are the hormones involved?
What is light sleep?
Light sleep, also known as shallow sleep, is a non-REM stage sleep that is known because it’s easier to wake someone up during a light sleep. Noises, temperature, touch, and movement can easily wake us up. We are more easily and readily awoken in light sleep. Sleep inertia, that feeling of grogginess when we wake up, is less powerful when we wake up from a light sleep than from any other form of sleep. Sleep itself is incredibly important in general because a poor quality of sleep or a reoccurring lack of sleep can lead to an increase in disorders like diabetes, depression, hypertension, cardiovascular disease, and obesity.
What is the difference between light sleep and deep sleep
Light sleep and deep sleep are terms thrown around a lot when talking about sleep. Deep sleep, also known as delta sleep, slow wave sleep, or N3, is defined as “a time of nearly complete disengagement from the environment,” according to Psychology Today.
When we dream during light sleep, it’s different than when we dream during a deeper REM sleep because the light sleep dreams don’t form stories. If we wake up during a dream in light sleep, we can remember that we had the dream, but we probably won’t be able to form any coherent narrative about them. Light sleep dreams come from images and brain epiphenomena like emotions and memories.
What are the stages of sleep?
Sleep stages, also known as the circadian cycle, was a phenomenon discovered by Alfred Lee Loomis, an American scientist, in the 1930’s after they began doing EEG recordings on people sleeping throughout the night. Our sleep changes throughout the night, and each stage was shown in the EEG. By the 1960’s, scientists knew that we had five stages of sleep and were able to identify what each stage meant. Overall, we have REM sleep and non-REM sleep. However, it can get more specific and be broken down into five stages. The five stages of sleep (sleep cycles) we pass through are:
- Stage 1 is when we drift in and out of sleep and can be easily awakened. Our eyes tend to move slowly and our muscles experience lower activity. Stage 1 is when people can experience the sensation of falling due to muscle contractions.
- Stage 2 is when our eye movement stops and our brain waves become slower and slower with the occasional rush of rapid brain waves. Stage 2 is when our body temperatures begin to drop and the heart slows down because our body begins to prepare itself for a deeper sleep. When people are awakened from Stage 2, they often deny they were sleeping or claim that they were already awake.
- Stage 3 is a form of deep sleep that happens when extremely slow brain waves (known as delta waves) are interspersed and combined with faster, yet smaller brain waves. Stage 3 is when people can experience parasomnias (night terrors, talking during one’s sleep, sleepwalking, or wetting the bed) because of the transition between non-REM sleep and REM sleep.
- Stage 4 occurs when our brains produce delta waves almost exclusively. When woken from Stage 4, people are usually disoriented for a few minutes.
- Stage 5 is known as REM– a stage that stands for Rapid Eye Movement and happens when our brain waves mimic the activity that happens during our awake state. Our eyes remain closed but will move from side-to-side- usually related to the brain activity, like dreams, that happens during the REM stage.
A complete sleep cycle (from Stage 1 → REM → Stage 1) takes about 90-110 minutes with each stage lasting roughly 5-15 minutes. However, the amount of time each of us spends in our sleep cycles depends on our age. Infants will spend about 50% of their time asleep in the REM stage. Adults will spend about 50% of their sleep in Stage 2, 20% in the REM stage, and 30% in Stages 1,3, and 4. We progressively spend less time in REM sleep the older we get.
Light sleep occurs within the first two sleeping stages. Stage 1 is mainly a transition between Stage 2 and waking up. Stage 1 also makes up about 3% of our total sleep time. Stage two is almost entirely light sleep. Adults spend about half, if not a little more, of our total sleep time in light sleep.
How does light sleep work?
Light sleep is tracked using an analysis of electroencephalographic rhythms (EEG) to help discover what happens while we sleep. After placing electrodes, little electrical conductors, on the scalp of someone sleeping, you can see the patterns of rhythmic discharges of brain neurons through the thalamocortical system. Our brain waves change depending on the stage of sleep we are in.
Sleep spindles and K-complexes are two of the electromagnetic waves seen through an EEG. Sleep spindles are little sudden bursts of back-and-forth brain activity that is produced in the nucleus of the thalamus during Stage 2. They are known as “spindles” because of how they look printed on an EEG. It’s believed by neuroscientists that these spindles on the EEG represent the transfer of facts and memories from one section of the brain to another. K-complexes have established brain waves in Stage 2. They don’t look or act like sleep spindles. Instead, they are large brain waves that react to external stimuli (noise, movement, etc.) while sleeping.
Sleep and the brain
Sleep plays a large role in how our brains function, including how our nerve cells, known as neurons, are able to communicate with each other. Furthermore, our brains remain rather active while we sleep During light sleep, our bodies rest and cell repair occur- though not to the extent it does in deeper sleep. Neuroscientists have suspected that our brain transfers memories from our short-term memory to our long-term memory during Stage 2. Essentially, our memory is “backed-up,” A recent study has found that sleep removes the toxins that we accumulate in our brains while we are awake.
There are several parts of the brain that sleep affects greatly:
- The hypothalamus contains a large group of nerve cells that act as a control center for sleep. This is because the hypothalamus has the suprachiasmatic nucleus (SCN), a cluster of cells that receive information about light exposure in our eyes. Damage to the SCN can cause issues with our bodies knowing when to get sleepy because they won’t receive the signals that “it’s dark outside so you should sleep” properly. Blind people can have an ability to sense light and using the SCN is how they are able to modify their sleep cycles.
- The pineal gland is located between our two brain hemispheres and receives signals from the SCN and produces melatonin. Scientists theorize that the ups-and-downs of melatonin production in our brains over time are important for matching the body’s external cycle of lightness and darkness.
- The brain stem (including the pons, medulla, and the midbrain) communicates with the hypothalamus to control the transitions between our awake state and our sleeping state. Sleep-promoting cells produce a brain chemical called GABA, gamma-Aminobutyric acid, which acts to help reduce the activity in our brain stem and hypothalamus. The brain stem also sends messages that signal our muscles to relax, essential for our body posture and our limb movements, which help us not physically act out when we dream.
- The thalamus relays information from our senses to the cerebral cortex, where we process our short-term memories to become long-term memories. When we are in a stage of light sleep, the thalamus quiets and helps us tune out the rest of the word.
- The basal forebrain is located near the bottom and front of the brain and it promotes our states of sleep and wakefulness. Adenosine, a chemical made from our cells when they consume energy, is released in our basal forebrain and supports our sleep drive. Caffeine counteracts adenosine.
Sleep and hormones
Our brains begin to know that we are ready for bed by activating clusters of sleep-promoting neurons. These neurons begin to “switch off” brain activity and begin to signal cells to relax.
- GABA, gamma-Aminobutyric acid, comes from the brain stem and is a neurotransmitter (brain hormone) associated with muscle relaxation and sleepiness.
- Norepinephrine and orexin, also known as hypocretin, are produced in the hypothalamus and they keep parts of the brain active while we are awake. They also control our appetite. When GABAs pass through the brain, our hypocretins begin to become less active.
- Acetylcholine is the most widely spread neurotransmitter that is produced by our nervous system. The purpose of acetylcholine is to stimulate muscle behavior.
- Adrenaline, also called epinephrine, and commonly known as the fight or flight hormone, is produced in the medulla as well as in some of our central nervous system. Cortisol, like adrenaline, is a stress hormone produced in the WHERE. Both of these hormones contribute to the rhythm of our heartbeats. When our hearts beat fast, our relaxation brain hormones are produced and it makes it difficult to fall asleep.
- Serotonin, derived from tryptophan, is what makes us sleepy after we eat turkey. It comes from our central nervous system but also lives in our blood platelets and our digestive system. Its entire purpose is to be a natural mood stabilizer.
- Melatonin is the brain-produced hormone that helps us get sleepy and comes from our pineal glands. Its main role is to be the body’s natural pacemaker- signal the time of day and regulate our internal clock.
How much light sleep do you need?
Sleep works like our shoe sizes- everyone’s need differs. Some people need more sleep than others to function. Although, it is scientifically thought that on average babies need about 12-18 hours of sleep a day. Kids need about 10-11 hours. Teenagers, contrary to popular belief, need about 8.5 hours of sleep a night. Adults can do with 7-9 hours of sleep.
However, babies barely spend time in light sleep. When an EEG is done on a baby, sleep spindles begin don’t show up until the baby is 6-8 weeks old. After that, the more the baby and the baby’s brain grow up, the more time they spend in light sleep. Adolescents and teenagers spend about 3.5-5 hours a night in light sleep. Middle-aged people can often experience a decline in deep sleep, which raises their time spent in light sleep. Many people become “light sleepers” as they age because they suffer from fragmented sleep– dipping in and out of sleep. However, the sleep that they are dipping in and out of is often light sleep.
Some sleep scientists claim that it doesn’t matter whether or not you get lots of light sleep because you’ll make up for the lost time with deeper sleep and REM sleep.
The benefits of light sleep
Light sleep is essential to our sleep cycle. Our bodies are able to rest, our cells repair themselves, and our memory is “backed-up” all during light sleep.
How to track light sleep
- There are some alarm systems, like the Eight Smart Alarm or the Sleep Cycle Alarm, that uses sensors in its sleep tracker to detect when your body is in light sleep. It will then wake you up when you are within a half hour of when you set your alarm and in your lightest sleep so you’re better able to wake up refreshed.
- Fitness bands, like a Fitbit or Jawbone, also are an available light sleep tracker. You can wear the fitness band on your wrist and it can track your sleep. When you sync the fitness band to your phone, you can see (depending on the fitness band) how much light sleep and REM sleep you got the night before.
Let us know how you track light sleep in the comments below!
Anna is a freelance writer who is passionate about translation, psychology, and how the world works.