by Kieran O’Mahony, University of Washington LIFE Center
If you have teens living in your home, they probably treat their alarm snooze button like a whack-a-mole. This obsession with sleeping in, staying up late and maintaining irregular sleep patterns may seem like a slovenly waste of time. Not really!
While asleep, our brains are not shut down. In fact our brains are a flurry of activity moving through a predicable cycle of 5 stages every 90 minutes or so. Even though progress through these sleep cycles is relatively predictable, each individual has unique sleep needs and patterns based on an individual circadian rhythm.
Memory Consolidation is what happens when information and other activities that occurred during the conscious state (daytime) are processed in an unconscious state (sleep time). Rapid Eye Movement (REM) sleep is the last stage of sleep. It is in this stage that the brain is busiest, retracing events that occurred during the day, dreaming and consolidating memories from the day. When we are dreaming our bodies are comatose so that we do not act out our dreams.
Restorative Actions take place in non-REM sleep — a stage prior to REM sleep that is characterized by restorative functions, which are essential for health and fitness. It is at this stage that healing of tissues occurs; muscles grow after working out that day, and strength returns after illness.
Teens & Sleep
Adolescents require more sleep than adults (Taylor, Jenni, Acebo, & Carskadon, 2005) and their circadian rhythms shift – something that makes early morning less productive for them (Carskadon, 1990). They experience a phase delay based on melatonin levels.Additionally, they spend more sleeping time in the REM stage than older adults and younger children (Roffwarg, Muzio, & Dement, 1966). This is a good thing and parents should understand why.
Five Stages of Sleep
Stage One: We drift off to sleep. We slowly lose consciousness. We enter Stage One of Sleep. This stage lasts maybe five or ten minutes. It’s very easy to wake a person up. It is a transition stage. We gradually enter Stage Two.
Stage Two: This stage lasts about ten or fifteen minutes. We start to look like a sleeping person – our breathing gets really deep; we exhibit a sleep posture (slump over etc.); the heart rate starts to drop; we take deeper breaths as we enter the deeper stages of sleep.
Stages Three and Four. This is what many people think of as a very deep sleep. During these stages, scientists believe that this is where the restorative actions of sleep are taking place in the body. It is in these stages that all the things that we consider beneficial for a good nights sleep for our bodies take place. For example, the immune system starts to be restored; if we are fighting off a cold, this is the time when our immune system kicks into high gear. If we have been exercising, this is the time when our muscles grow; it is the time when we are losing weight, burning calories. These stages three and four can last anywhere from thirty minutes to an hour. It is really important to get these stages of sleep because they basically heal the body from all the wear and tear that has happened during the day. Sleep is healing the wear and tear within each individual cell in our bodies in terms of metabolism and restoring nutrients etc. Athletes need this time in particular because muscles are growing, and they replenish the energy source.
Figure 1. EEG waves that describe the five stages of sleep
Rapid Eye Movement: A really interesting thing happens next. We enter a period of sleep known as Rapid Eye Movement (REM)—because when we look at someone who is going through this stage of sleep, we can see their eyes rapidly moving underneath their eyelids. The remarkable thing is that the eyes are the only thing moving – the entire body is relatively paralyzed (no twisting or turning). What stages three and four are for the body, it’s thought that REM sleep is for the mind and for the brain. The idea is that during REM sleep, consolidation of the things we learned during the day is occurring. The brain is processing the information that was experienced during consciousness—both in terms of (i) consolidating memories that we want to keep, and (ii) getting rid of memories that we don’t want to keep.
A lot of things that we experience during the day are not important and even though they might have been important for a few moments at that time, they are not important in the long scheme of things. During REM sleep we actually forget that stuff while we remember the things that are really important to us. That’s why it is important to get a good amount of REM sleep because it consolidates all that information. It appears that we replay these memories while we are sleeping—whether it is an event that happened or even muscle memory (as in people learning to play ball) there is motor memory in terms of our brain remembering exactly the sequence of muscle movements we did in order to be successful. Thus, in REM sleep we consolidate the good things and get rid of the bad things.
Then we cycle back to Stage One after REM is over and slowly progress through the five stages two or three times each night.
Quality sleep is defined as the ability to transition through these stages without having a lot of disruptions (being woken up) — smooth transitions from stages one through four and into REM sleep and cycling back through three or four times per night.
Sleep for Adolescents: Sleep is different for newborns than for teenagers. It seems that there is no textbook definition of what is a normal sleep cycle as one gets older. For adolescents however, there is a layer of complexity added to sleep. It’s easy to understand as adults that it is important to rejuvenate the body and to rejuvenate the mind and brain. But for adolescents, there is more going on. Think about the physiological changes that are taking place in an adolescent. Not only is there a tremendous amount of learning happening in the brain during adolescence, but also there is a tremendous amount of normal development that requires sleep. For example, growth hormone is released during adolescence.
If one doesn’t get enough sleep then one might not get enough growth hormones circulating through the body. Consequently an adolescent who is severely sleep deprived and who accumulates a lot of sleep debt might not have normal levels of growth hormone circulating at night and might not grow as much as they could or should. We usually think about the negative affects of sleep deprivation and sleep debt in the short term, but in the case of adolescents it might have an impact on them for their whole lives. They might not have the same bone density that they would have normally acquired; they might not grow as tall as they normally would have. This is a time when all the changes become permanent and so for adolescents it is vital to get quality and quantity sleep.
Midnight Teaser: Why is it so hard to keep our eyes open when we are sleep deprived (eyelids are heavy, drooping uncontrollably)?
The brain knows when it’s time for sleep. It stops pumping the neurochemical acetylcholine (transmitter at neuromuscular synapses) into our eyelids. This is the neurotransmitter that is used when we move our muscles – our peripheral nervous system that goes out to our muscles and secretes acetylcholine. It actually stops pumping in the neurotransmitter – so the eyelids from our standpoint are getting really heavy, because it takes more and more effort to secrete more and more acetylcholine. The brain is essentially tricking us – forcing us to go to sleep.
Students Dilemma. Student has an exam tomorrow. She does not know (or assumes she does not know) the information. The dilemma is this: should she spend more time awake learning it or does she spend that time sleeping and feeling more refreshed and consolidating it.
The trouble is we often think we don’t even have enough to consolidate so we stay up all night… pull an all-nighter before the test (I can’t consolidate something I don’t know).
Circadian Rhythm: recurring naturally on a twenty-four-hour cycle, even in the absence of light fluctuations.
Memory Consolidation: The brain is processing the information that was experienced during consciousness—both in terms of (i) consolidating memories that we want to keep, and (ii) getting rid of memories that we don’t want to keep.
Melatonin: a hormone secreted by the pineal gland that inhibits melanin formation and is thought to be concerned with regulating the reproductive cycle.
Sleep: a condition of body and mind such as that which typically recurs for several hours every night, in which the nervous system is relatively inactive, the eyes closed, the postural muscles relaxed, and consciousness practically suspended.
REM: Rapid Eye Movement – a jerky motion of a person’s eyes occurring in REM sleep.
Non-REM: Stages one through four of the sleep cycle.
Sleep Hygiene: Healthy approach to sleep time that enables quality and quantity for the human mind and body to experience rejuvenation.
Carskadon, M. (1990). Patterns of sleep and sleepiness in adolescents. Pediatrician, 17, 5-12.
Roffwarg, H., Muzio, J., & Dement, W. (1966). Ontogenetic development of the human sleep-dream cycle. Science, 152, 604-619.
Taylor, D., Jenni, O.G., Acebo, C., & Carskadon, M. (2005). Sleep tendency during extended wakefulness: insights into adolescent sleep regulation and behavior.
Journal of Sleep Research, 14, 239-244.
Tokuhama-Espinosa, T. (2010). The new science of teaching and learning: using the best of mind, brain and education science in the classroom. New York: Teacher College Press.
Carter. M., et al., (2011). Optogenetic disruption of sleep continuity impairs memory consolidation. Proceedings of the National Academy of Sciences. 108, 32, 13305-13310.