Before scientists had a clear understanding of sleep, they thought that the brain “turned off” or became inactive at night to reset itself from daily activities. Now researchers know that the brain goes through a series of cycles during sleep that is sometimes more active than when we’re awake. Understanding these cycles is an important part of making healthy choices that result in the best sleep possible.
Many inventions today such as the sleep cycle calculator have made sleep an easier process. You can also download a sleep cycle app on your phone to tell you when you should go to bed based on what time you need to wake up. With all of this new technology available, it’s hard to believe that 45 percent of Americans suffer from sleep problems (1). Here’s what you need to know about your sleep cycle as well as some tips for regulating it.
The two systems that determine your sleep cycle are known as the sleep-wake homeostasis and the internal biological clock. These two systems work together to sync your sleep cycle based on internal and external factors. Before scientists began studying sleep in the 1920’s, they thought that the brain became inactive at night during sleep and restarted in the morning upon waking. Researchers now know that this couldn’t be further from the truth.
In 1929, scientists began using an EEG to record brain activity during sleep. This allowed them to determine that sleep was a much more complicated process than originally thought. They concluded that the brain was highly active during sleep and did not turn off at all. Scientists also began to monitor muscle activity and eye movements during sleep to determine the two different types of sleep: rapid eye movement (REM) and non-rapid-eye movement (NREM).
REM sleep is identified on an EEG by small and fast brain waves, along with rapid eye movements. Dreams occur during REM sleep, and experts think it has something to do with why the eyes move rapidly during REM sleep. When people are woken up during REM sleep, it’s often in the middle of a dream.
Some sleep calculators work by determining a formula that prevents you from waking up during REM sleep. It is believed that waking up during REM sleep leaves you extra tired and groggy. On the other hand, people report dreaming less frequently when woken up during NREM sleep. Total body paralysis is most commonly experienced during REM sleep. Scientists believe this is because of a neurological barrier that prevents movement (2).
You have two internal biological systems that control your sleep cycle. The circadian cycle and the sleep-wake homeostatic processes work together to make up your inner sleep cycle. Your circadian cycle collaborates with a wide variety of body functions to determine your individual sleep needs, including body temperature, hormone levels, and metabolism. It is responsible for making you feel tired at night and determining what time you will wake up in the morning.
The circadian cycle is based on your body’s 24-hour biological clock. It synchronizes to environmental cues such as time of day, temperature, and light, but it’s so powerful that it also works when these signals are not present.
The sleep-wake homeostasis process reminds you to go to sleep after a particular time. It is responsible for regulating the intensity of sleep. Every hour you are awake, your homeostasis process reminds you that you are becoming sleep deprived. Your homeostasis process is affected by stress, your sleep environment, what you eat and drink, and what medications you take (3).
Exposure to light is by far the most important factor that affects your sleep cycle. Located in the retina of your eyes are specialized cells that tell your brain whether it’s time to go to bed or wake up. When you’re exposed to darkness, your body produces a hormone called melatonin that makes you sleepy. Melatonin levels are decreased during the daylight or anytime you are exposed to light, such as when you wake to television late at night. People who work the night shift or travel across several different time zones commonly experience a disruption in their sleep cycle.
Several parts of your brain are involved in the sleep process. Your hypothalamus is a small structure located deep in the brain that contains a group of nerves that control how well you sleep. The hypothalamus contains the suprachiasmatic nucleus or SCN, which is made up of thousands of cells that determine your exposure to light. Your SCN sends messages to the brain to tell it when to produce chemicals that help you fall asleep. People who have erratic sleep schedules damage their SCN from being able to regulate sleep mechanisms correctly.
The brain stem, located at the bottom of the brain, works with the hypothalamus to control your sleep and wake transitions. The brain stem is made of the following structures: pons, medulla, and midbrain. It also contains cells that promote sleep by generating a chemical called GABA, which is needed to settle arousals in the brain so that you can fall asleep. The pons and medulla are required to relax your muscles so that you can act out your dreams (3).
The thalamus relays messages from the cerebral cortex, which is the part of your brain needed to process short term and long term memory. When you sleep, the thalamus quiets down and lets you tune out the outside world so you can sleep. When you dream, the thalamus becomes active and sends messages to the cortex that illustrate images, sensations, and sounds associated with dreaming.
Located between the brain’s two hemispheres is the pineal gland. Its job is to receive messages from the SCN to produce melatonin. Over time, the regulation of melatonin can help you sync your circadian rhythm to match that of your external environment, such as exposure to light. Located near the bottom front of the brain is the basal forebrain, which is part of the midbrain that promotes sleep and wakefulness by determining your arousal reactions. The basal forebrain releases a chemical called adenosine that helps you become sleepy. Caffeine works by blocking adenosine to keep you feeling alert, which is why you shouldn’t drink it close to bedtime or when you want to sleep (3).
Finally, the amygdala is an almond shaped structure in the brain that processes emotions. It is activated when you dream. Your brain is responsible for omitting many different chemicals that regulate sleep. As you get ready for bed at night, clusters of neurons develop in the brain to cause you to become sleepy. These neurons send signals called neurotransmitters that turn off cell activity that is responsible for arousal to stimulate relaxation.
GABA is an example of a neurotransmitter that helps your muscles relax. It has a relaxing effect on the brain that allows you to fall asleep easier. Orexin, also known as hypocretin, and norepinephrine are needed to stimulate the brain when we are awake. Other transmitters responsible for influencing the sleep-wake cycle include histamine, adrenaline, acetylcholine, serotonin and cortisol.
Sleep Cycle Stages
Your sleep cycle can be broken up into the following four stages:
Most adults begin their sleep cycle in NREM sleep. During the first stage of sleep, the brain experiences alpha activity, which means that you are in a relaxed state of wakefulness with your eyes closed just before drifting off to sleep. Your brain waves indicate a mixed frequency pattern with low voltage on the EEG. It only takes you a few seconds to fall asleep once N1 occurs. This stage lasts anywhere from one to seven minutes.
The second stage of sleep is N2. It lasts around ten to 25 minutes. During N2, your brain waves gradually give way to a higher voltage. The final stage of NREM sleep is N3. It lasts 20 to 40 minutes and is also referred to as the deep sleep stage. As you progress into N3 sleep, you become less responsive to stimuli around you, and it’s harder for you to wake up.
You usually enter REM sleep approximately 90 minutes after you fall asleep, but this number is different for everyone. The average person has five to six 90 minute sleep cycles each night. REM sleep is the final stage of this 90-minute cycle. During REM, your brain becomes more active and begins to dream. Your eyes experience a rapid jerking movement, and your heart rate and blood pressure increase.
REM sleep is highly restorative, meaning that it helps you recover from the day’s activities. Your brain cells shrink, and the body naturally detoxes waste materials from them. During REM sleep, your brain strengthens your memory and learning components. Sleep calculators work by determining when you’ll enter REM sleep and making sure you are not woken up during this critical time.
How To Use A Sleep Calculator Or App To Determine Your Ideal Sleep Cycle
Because your sleep cycle is such a complicated process, it doesn’t take much to throw it off. Stress, improper diet, eating too late at night, and lack of exercise can all keep you awake at night. The best way to get your sleep back on track is to determine your ideal bedtime. A sleep calculator is designed to help you do just that.
Although your sleep cycle is uniquely different from others, a sleep calculator can help you determine when you go to sleep based on what time you need to wake up. It uses your wake up time to calculate how many 90 minute cycles you will go through based on what time you go to bed. Then it gives you several bedtime options. For example, if you need to wake up at 6 am, your sleep calculator recommends that you go to bed at one of the following times: 8:45 pm, 10:15 pm, or 11:45 pm.
You can find most sleep calculators on the internet for free. Here are some examples:
You can also find a sleep calculator app for your phone, but some of them may cost money. Some smartphone apps come with wearable technology to determine your sleep patterns and make suggestions based on your personal needs. An app can send a signal to your phone when it’s time to go to bed. It might be a good idea to try a sleep calculator on the internet for free and then download an app to your phone if it works for you. Here are some examples:
To use your sleep calculator or app, enter the time you need to wake up. The sleep calculator will then calculate what time you need to go to bed. Some sleep calculators give you the option of calculating what time you should wake up if you were to go to bed immediately. If you choose not to use a sleep calculator, you can try to determine your sleep cycle by going to bed when you feel tired and allowing yourself to sleep until you wake up naturally.
Although there is no magic number, your age can help you determine how much sleep you need at night. Most adults need about seven to nine hours while babies need up to 18 hours a day. Some research shows that you cannot make up missed sleep, so be sure to stick to a nightly routine for best results. A good rule of thumb is to wake up at the same time every day, even if you stay up past your bedtime. This will help sync your circadian rhythm to natural environmental factors such as light and darkness so you can get the most restorative sleep possible.