| What isSleep... |  |
| What isSleep... | |
 We spend about 8 hours/day, 56 hours/week, 224 hours/month and 2,688hours/year doing it...that's right...SLEEPING. One third of our lives weare apparently doing nothing. But is sleep really doing nothing? Itlooks like it...a person's eyes are closed; muscles are relaxed; breathing isregular; there is no response to sound or light. However, if you takea look at what is happening inside the brain, you will find quite adifferent situation - the brain is very active.Scientists can record brain activity by attaching electrodes to the scalpand then connecting these electrodes to a machine called an |
Sleep follows a regular cycle each night - the EEG pattern changes in apredictable way several times during a single period of sleep. There aretwo basic forms of sleep: slow wave sleep (SWS) and rapid eye movement(REM) sleep. (REM sleep is sometimes called"paradoxicalsleep"). Infants spend about 50% of their sleep time in SWS and50% in REM sleep. Adults spend about 20% of their sleep time in REM and80% in SWS sleep. Elderly people spend less than 15% of their sleep timein REM sleep. |
 These lines represent the EEG(electroencephalogram) which shows a record of brain activity; theEMG (electromyogram) shows muscle activity; theEOG (electroculogram) shows eye movements. Lookat the differences in the EEG, EMG and EOG during waking, REM sleep (RapidEye Movement Sleep) and SWS sleep. |
| REM sleep is when dreamingoccurs. During this stage of sleep the eyes move back and forth rapidly. Sleep researchers discovered this when they woke people up duringREM sleep. These people said that they were just dreaming. Notice thatthe EEG pattern during REM sleep is similar to the EEG when you are awake. However, the EMG is very quiet during REM sleep - one theory is thatduring REM sleep, the muscles are inactive so that we will not act out ourdreams. This also means that sleepwalkers are not in REM sleep and arenot acting out their dreams. SWS sleep is actually 4 different stages of sleep (Stage 1, Stage 2, Stage3 and Stage 4) with different EEG patterns.
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 While weare asleep,our brains are on a bit of a "roller-coaster" through these differentstages of sleep. As we drift off to sleep, we first enter stage 1 sleep.After a few minutes, the EEG changes to stage 2 sleep, then stage 3sleep, then stage 4 sleep. Then it's back up again: stage 3, stage 2,then a period of REM sleep...then it's back down again, and back up again,and down again...you get the picture. As shown in the figure below, in an8 hour period of sleep, thebrain cycles through these stages about 4-5 times. |
| Did you ever thinkabout how much you sleep and dream? The "average" human sleeps about 8hours every day. That's one third of your life! In other words, you sleep for about 122 days every year. A 75 year oldperson would have spent a total of about 25 years asleep. There is a widerange in the amount of time differentanimals spend sleeping. As for dreaming...we enter REM sleep about 5 times in an average 8 hourperiod of sleep. If we assume that we dream during each of these REMperiods, then in one year, we will have had 1,825 dreams! Of course wedon't remember all of these dreams. A 75 year old person would have about136,875 dreams!
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Why Sleep?Why sleep at all? It seems like a big waste of time. Think of allyou could be doing if you did not sleep. Nevertheless, sleep appearsto be necessary. There is a continuing debate going on as to why wesleep. Why do most animals sleep? How much sleep isrequired?Most "higher" animals appear tosleep during some portion of the day and/or night. - they arequiet; they rest; they do not move. No one knows for sure why we sleep, but here are 2 basic theories:
Sleep as a Restorative Process This theory of sleep suggests thatsleep helps the body recover from allthe work it did while an animal was awake. Experiments have shown thatthe more physical exercise an animal does, the more SWS an animal willhave. Also, if people are deprived of SWS by waking themup each time they get to stage 4 sleep, then they complain of beingphysically tired. If people are deprived of REM sleep by waking them up each time the have REM type EEG patterns, they can get anxious andirritable. If animals are deprived of REM for several days and thenallowed to get an undisturbed period of sleep, animals will go into "REMrebound" - this is when REM periods of sleep will happen more often and for a longer time than normal. Sleep, especially REM sleep, has also been thought to be important formemory and learning. Perhaps sleep in some way helps in the formation ofmemories. Sleep as an Adaptive ProcessSleep may have developed because ofa need of animals to protect themselves. For example, in some animals,the search for food and water is easier in the day when the sun is out. When it is dark, it is best for these animals to save energy, avoidgetting eaten, and avoid falling off a cliff that they cannot see. It isinteresting to note which animals sleepthe most and which sleep the least. In general, animals that serve asfood for other animals sleep the least. |
 | Sleep disorders affect up to 70 million people in the United States. This costs about $100 billion each year in accidents, medical bills andlost work. (Statistic from Brain Facts, Societyfor Neuroscience, 1997) |
 | Trythese sleepexperiments. |
For more information on sleep, see:
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Stages of Sleep
Scientists have recordedsleep-like EEG patterns in birds, reptiles and mammals. Whetherinsects and other invertebrates also "sleep" is unclear.
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