Just as deep sleep renews the body, REM-sleep renews the mind by playing a key role in learning and memory. During REM-sleep, our brain consolidates and processes the information we have learned during the day, forms neural connections that strengthen memory, and replenishes its supply of neurotransmitters, including feel-good chemicals like serotonin and dopamine that boost our mood during the day.
Improving our overall sleep will also increase our REM-sleep. If we aren’t getting enough deep sleep, our bodies will try to make that up first, at the expense of REM-sleep.
REM-sleep in adult humans typically occupies 20–25% of total sleep, about 90–120 minutes of a night’s sleep. REM-sleep normally occurs close to morning. During a normal night of sleep, humans usually experience about four or five periods of REM-sleep; they are quite short at the beginning of the night and longer toward the end. Many animals and some people tend to wake, or experience a period of very light sleep, for a short time immediately after a bout of REM-sleep. The relative amount of REM-sleep varies considerably with age. A newborn baby spends more than 80% of total sleep time in REM-sleep. During REM-sleep, the activity of the brain’s neurons is quite similar to that during waking hours; for this reason, the REM-sleep stage may be called paradoxical sleep.
The two main types of sleep are rapid-eye-movement (REM) sleep and non-rapid-eye-movement (NREM) sleep. On an EEG, REM-sleep, often called “active sleep,” is identifiable by its characteristic low-amplitude (small), high-frequency (fast) waves and alpha rhythm, as well as the eye movements for which it is named. Many sleep experts think that these eye movements are in some way related to dreams.
Typically, when people are awakened from REM-sleep, they report that they were dreaming, often extremely vivid and sometimes bizarre dreams. In contrast, people report dreaming far less frequently when awakened from NREM-sleep. Interestingly, during REM-sleep muscles in the arms and legs are temporarily paralyzed. This is thought to be a neurological barrier that prevents us from “acting out” our dreams.
The EEG recorded during REM-sleep shows very fast and desynchronized activity that is more random than that recorded during NREM-sleep. It actually looks similar to the EEG (low voltage with a faster mix of frequencies) from when we are awake. REM-sleep is characterized by bursts of rapid eye movements. The eyes are not constantly moving, but they dart back and forth or up and down. They also stop for a while and then jerk back and forth again. Always, and just like waking eye movements, both eyes move together in the same direction. Some scientists believe that the eye movements of REM-sleep relate to the visual images of dreams, but why they exist and what function they serve, if any, remains unknown.
Additionally, while muscle tone is normal in NREM-sleep, we are almost completely paralyzed in REM-sleep. Although the muscles that move our bodies go limp, other important muscles continue to function in REM-sleep. These include the heart, diaphragm, eye muscles, and smooth muscles such as those of the intestines and blood vessels. The paralysis of muscles in the arms and legs and under the chin show electrical silence in REM sleep. On an EMG, the recording produces a flat line. Small twitches can break through this paralysis and look like tiny blips on the flat line.
Sleep is a cyclical process. During sleep, people experience repeated cycles of NREM and REM-sleep, beginning with NREM stages. This cycle lasts approximately 90 to 110 minutes and is repeated four to six times per night. As the night progresses, however, the amount of deep NREM sleep decreases and the amount of REM-sleep increases.
REM-sleep and personal development
Researching REM-sleep is one of the most fascinating sleep study areas. Because the amount of REM-sleep varies considerably between different age groups, researches assume that REM-sleep is linked, one way or another, to development of an individual. We believe that REM-sleep is especially necessary for brains to function and for this specific reason half of new born babies’ sleep is indeed REM-sleep. Respectively, adults only have 1.5-2 hours of REM-sleep a night.
Furthermore, if we compare the amount of REM-sleep between a 20-year-old and a 60-year-old we can learn that the amount of REM-sleep declines as we age. This decline can also explain why older people can’t remember new events as clearly as young. During REM-sleep we store new memory material and therefore capabilities to deal with new information and memorise new events gets more difficult as the amount of sleep (and especially REM-sleep) declines.
During deep NREM-sleep (stages 3 and 4 described in sleep stages) at early night we learn new stuff. This learning is linked with long-term memory. REM-sleep is so important for the brain that other bodily systems will be exposed in favour of REM-sleep! For example, in the early hours during REM-sleep, blood pressure fluctuates, heart beat varies and arrhythmia is possible even with a completely healthy person. As body systems slow down, only local blood circulation in our brains speeds up. The human being is then totally limp and his/her heart and lungs operate lazily. This is a time when both arrhythmia and cerebral embolism are plausible.
REM-sleep and memory
Our bodies rest at night, but our brains don’t. Our brains deal with the daily events and experiences, create relevant connections and fulfil dried up energy resources. Experts believe that sleep has a vital role to play attaching memories at night.
Memory has been typically divided into three categories based on how long the memory lasts:
- The sensory memory – this acts as storage for the stimulus received by our senses: what we see, hear, taste, smell, touch and feel. This site stores short-lived memories of seconds or even less.
- The working memory – this stores memory for a little longer but also processes information before forwarding it on to the third memory site.
- The long-term memory – this stores information anywhere between an hour to a lifetime.
The working memory acts as an intermediary for information we are dealing with every moment of our lives. It is often burdened with data and constantly working over-time about day thinking, calculating, assessing, remembering, communicating.
Lively sleep during the early hours reminds us of our waking state because then human beings deal with complicated matters unconsciously. If an unsolved issue has been troubling our minds, we can wake up in the morning with a clear solution at hand. This is possible because during sleep, and especially during REM-sleep, nerve cells discuss with each other and ‘agree’ how the new information is organised and managed. At the same time, unnecessary information is deleted. This all said, it’s good to remember that we can’t program brains to solve a specific issue during a night – even though that would certainly sound lucrative!
However, the working memory is only of finite size and can only hold a limited amount of information. Yet in today’s 24/7 society most of us feel that we need to be available all the time and share our pillows with smart-phones and tablets. What’s worse, it seems that mega-multitasking is seen as virtue.
The working memory only frees up storage when we go totally ‘offline’, daydream and/or sleep. In fact, we try to work against our natural limitations. As a consequence, our brains start ‘boiling’ and sleep is disturbed. It appears that this memory debt that accumulates during the day interferes with the memory consolidation process at night.
Dr Remina Ramlakhan strongly believes that this is where much of our Tired but Wired sleep can come from. She believes that technology and the resulting lack of ‘downtime’ has expanding our need for REM sleep that has given rise to this noisy, jangling, information-filled sleep that many of us complain of. We are sure progressing and evolving as human beings but perhaps the technology evolution beats our human pace.
REM-sleep and creativity
There’s a strong indication that REM dreaming is vital for processing of creativity and sorting our inner world. Ernest Hartmann is a psychologist who has studied the personality difference between ‘long’ and ‘short’ sleepers. He found out that long sleepers tend to be creative, more introverted, more emotional with complex personalities. By contrast, the shorter sleepers tended to be more easy-going, contended and socially-adept. This all sounds a bit black and white and categorical yet it can indicate that REM dreaming is essential for creativity.
A study reported by the University of California, San Diego School of Medicine suggests that REM-sleep enhances creative problem solving. The key finding suggests that REM-sleep actually fosters unique associations, compared not only to non-REM sleep but also waking consciousness. From the article at ScienceDaily: “We found that – for creative problems that you’ve already been working on – the passage of time is enough to find solutions,” said Mednick. “However, for new problems, only REM-sleep enhances creativity.”
The phenomenon of REM-sleep and its association with dreaming was discovered by Eugene Aserinsky and Nathaniel Kleitman with assistance from William C. Dement, a medical student at the time, in 1952 during their tenures at the University of Chicago.