Although we may not even realize it, we spend a good portion of our lives sleeping. Despite sleep being essential to our lives, many people know very little about it, because we experience it without remembering or thinking about it. Perhaps two experiences of sleep we are aware of is that of becoming sleepy, and that of "dreams".
Basics of Sleep
Contrary to a long held conception that sleep is a simple process of merely "shutting down" our brains, the brain is very active when we are sleeping. Sleeping follows a five-stage cycle that usually takes 90 to 110 minutes to complete (1).
The five stages are grouped into one through four being Slow Wave Sleep (SWS) and stage five being Rapid Eye Movement Sleep (REM). Stage 1 is known as "light sleep". At this point we drift in and out of sleep, and so can be easily awakened at this point. In stage 2, our brain waves generally become slower and our eye movements stop. Stages 3 and 4 are known as deep sleep that involves extremely slow brain waves called delta waves. The difference between the two stages is that stage 3 has smaller waves mixed in with the delta waves while stage 4 only involves delta waves. In REM sleep, the brain is more active, but our muscles become temporarily paralyzed (1).
The difference between REM sleep and SWS is the difference in EEG (electroencephalogram-brain activity), EMG (electomymogram-muscle activity) and EOG (electroculogram- eye movements). When compared to our wake stage, the EEG frequency in SWS is less. When we are awake, our EEG Rate is about 8-25 Hz while when we are in SWS it is from 6-8 Hz in Stage 1, and decreases in frequency to as low as 1 Hz in Stages 3 and 4. Both muscle activity and eye movement are also noticeably lower. On the other hand, the EEG rate is more than 10 Hz for REM sleep, meaning the brain is as active as certain times when we are awake. Eye movement in REM sleep is also noticeably frequent than SWS, but muscle movement is almost unnoticeable. We breath more rapidly, our heart rate increases, and blood pressure rises but for some reason our limb muscles become temporarily paralyzed during REM (2).
Why we get sleepy, and what to do about it
Our bodies work on a circadian rhythm, controlled by an internal "clock". The clock is actually the Suprachiasmatic nucleus (SCN) located in the hypothalemus (1). Research has found that although we would naturally run on a 25-hour cycle, because sunlight regulates the clock, we run on a 24-hour cycle. Sunlight regulates this system by the retina sending signals to the SCN upon receiving sunlight, which then results in the SCN sending signals throughout our body including the pineal gland. This gland is responsible for regulating melatonin, a chemical that makes us drowsy. Travelling to different time zones, working at odd hours or plain bad sleeping habits can cause a disruption of the circadian rhythm. This disruption of the circadian rhythm results in being sleepy at odd hours, being unable to sleep when you should be sleeping, and in the long run potentially result to more severe symptoms (1).
The amount of sleep one needs usually reflects their age, but there are differences on a personal basis. Babies need about 16 hours of sleep while the elderly need only about 5 hours. And while a teenager needs about 9 hours, average adults need about 8 hours of sleep per night. Amazingly, one or two in a hundred adults can do with an average of 5 hrs per night, but on the other extreme some need as much as 10 hours per night. This personal difference is the reason different people will act differently even while getting the same amount of sleep (1). The amount of sleep required can be a reflection of how fast the sleep cycle progresses for that individual, the speed of recovery of tired neurons, and other factors yet unclear.
Although eight hours is the recommended sleep time for adults, but as many as 56% of the adult population report daytime drowsiness (3). In recent years our lifestyles including work, TV, talking on the phone etc., has resulted in a 20% decrease in average sleep time when compared to a hundred years ago (4). This startling fact can be seen from many of us being sleepy during the day. If we do not get enough sleep one night, our body needs to make up for that time the next time we sleep. This "sleep debt" is a reason why we sleep-in on weekends. As well, if we are unable to clear this "sleep debt" during the night, our body tries to catch up on sleep during the day, resulting in people sleeping at odd places and odd hours.
Many of us are sleepy during the day because of sleep deprivation, but even with enough sleep each night it is natural for humans to feel sleepy during the day. In the afternoon between the hours of 2 p.m. and 6 p.m., we are supposed to experience a sense of sleepiness. These hours correspond to being 12 hrs from 2 a.m. to 6 a.m., which are the hours of maximum sleepiness during the nocturnal hours (4). That is why young children, college students and retired elderly people who have the time during the day, take naps.
A brief nap is the best remedy for daytime sleepiness. Afternoon naps of about 20-30 minutes made up of restful non-REM sleep enables us to do away with fatigue, sharpen memory and attention, while improving our mood and memory (4). Naps are also good for catching up on sleep, but can never be as effective as getting night time sleep. Thus when writing papers or doing work, it is good to take a 20 or 30 minute nap to help you concentrate more and increase efficiency. But if you sleep 4 hours during the day so you can stay up the whole night to work is more harmful then helpful even if that is what you think your body needs.
If on average we sleep for eight hours every night, that means we have slept for a third of the day, and in turn meaning you sleep for a third of your life. Although it might seem like a waste of time, sleep is necessary and we cannot do without it. There is a strong relation between sleep and our health. Rats who are deprived of sleep can only live for three weeks even while the average life span is two to three years. For humans, sleep allows neurons used when we are awake to shutdown and repair itself. Because a lack of sleep will result in mood swings and poor health, not sleeping will allow us to be awake in terms of numbers of hours, but with a lack of concentration and constant fatigue we will be less awake. It's the difference between the quality and the quantity of the hours one is awake, so in the end it is not a waste of time to sleep.
DREAMS
All of us have experienced "dreams". Sometimes they are good other times they are bad (nightmares), while in still others they are just confusing. I have seen many dreams, and actually do not remember most of them. They seem very real, yet you just forget it really quickly. So exactly what are dreams?
We typically spend 2 hours a night dreaming and in 85 to 90% of REM awakenings a dream is reported (5). The REM stage has always been considered the most intriguing, not only because of its unique features in relation to the other stages, but because of its strong correlation to dreams. It has been experimented that most people who claim to see dreams are awakened from REM (2). REM sleep begins with the pons sending signals to the thalamus, which then goes on to the cerebral cortex. Signals from the pons that shut down neurons in the spinal chord is seen as the source of the limb muscle paralysis. REM's relation with the cerebral cortex is seen as the source of dreams. Some scientists say that dreams are the cortex's attempt to find meaning in the random signals it receives during REM sleep (1).
Although it is not fully proven, it is possible to see why the pons sends signals to shut down the limb muscles. In recent years it has been discovered that the paralysis prevents us from harming ourselves by acting out our dreams. There are people with a REM sleep behavioral disorder who act out their dreams and risk hurting themselves and others (6). The opposite of this form of REM sleep behavioral disorder is kanashibari (sleep paralysis) when we our conscious but are unable to move our bodies (2).
If a person gets 8 hours of sleep per night, they will go through about five sleep cycles. In the first sleep cycle the period of deep sleep (stages 3 and 4) are relatively long, while the REM stage is quite short. But as each cycle progresses the ratio decreases and thus the length of the REM stage increases that by morning, people are sleeping in stages 1, 2 and REM (1). That explains why people are more likely to see dreams when sleeping long hours (like on weekends).
Yet, recent research has shown that dreams are not limited to REM sleep. Dreams can actually occur in all stages of sleep, and even during sleep onset and relaxed wakefulness (when we are in a dark room with our eyes closed). Although the frequency of dreams reported when wakened from these stages are less than during REM, we have the potential to experience dreams in every stage (5).
Dreams are not mere hallucinations, but are usually somehow connected to the person, while not being a reproduction of a certain memory (5). Usually they are like fictional like stories, but clearly have organization. There has been some research connecting our "wake" self and our "dream" self. Usually, people's emotional state during the wake period is reflected in the emotional state of the person or a theme in a dream. But on the other hand, seeing a scary or violent movie before we sleep does not effect our dreams (5). If you are one of those people who do not want to see a scary movie before you sleep for fear of seeing a nightmare, it has been proven that there is no connection, so that belief is just an old-wives' tale. What the case is for most people is that they think about the movie in bed before they actually sleep, and their fear of the movie along with the dark surroundings of the room make it hard to go to sleep and cause a sense of fear. Although we increasingly have knowledge concerning dreams, unfortunately we still do not know the answer to the fundamental question of where themes for dreams come from.
Like many other things concerning behavior, we do not know the answer to many of the questions concerning sleep and dreams. Looking at the progress in science, I would not be surprised if many of these questions are answered in the oncoming years. Yet the questions I tried to take up in this paper are only a small aspect of sleep and dreams. I was just genuinely curious about sleep and dreams, because we do spend a good portion of our lives sleeping (should be one-third but most of us don't especially in college). Perhaps dreams are honest reflections of ourselves. A story where we are the main characters. It is honest because it covers many aspects of ourselves that we try to block out (maybe unconsciously). They reflect our fears, good and bad desires, and perhaps most importantly wishes. Ultimately, although sleep plays an important role in how we behave, dreams play the role of creating our behavior. Perhaps some people may say they do not need dreams, but I think that for better or for worse they are necessary in helping us define who we are.
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2) What is Sleepˇˇ, A brief overview of different aspects of sleep, includes many charts
3)Rest Assured: Naps are Good, An article on Naps, on its effect on performance
4)A Good Night's Sleep , Brief overview about sleep, and also covers naps
5)Basics of Sleep behavior: DREAMS, A descriptive article on different aspects of Dreams
6)Why We Sleep (or Can't), Article on why we sleep, what makes us sleepy