SLEEP CYCLES by Dr. D‚j… Vu "Sleep is sleep, right? I mean you're either asleep or you're not. So how come some nights you 'sleep good' and other nights you don't?" Sleep occurs in cycles, each of which are approximately 90 minutes long. Each stage of a cycle has its own measurable and easily recognizable physiological characteristics. This brief summary of each stage will provide you with an understanding of how dreaming and the quality of sleep are directly related to the individual stage. INITIAL STAGE ONE: Stage one occurs as we drift off to sleep and periodically throughout the night as we emerge from the deeper sleep stages for increasingly long periods of time. Physiological changes; heart rate slows, muscles relax. EEG patterns closely resemble those found in waking state. This stage will occur about every 90 minutes, four to seven times per night (depending on how long we sleep), and each succeeding period of dreaming in the cycle lasts longer than the preceeding one. (The initial Stage One period may last 5 to 10 minutes while the last one of the night may go on for 30 or 40 minutes.) Although imagery does occur, it is often described as "I was thinking about..." or "I was dreaming something but I'm not sure what." This imagery does is not of the quality and intensity characterized by a true dream. There is no rapid eye movement (REM) that is associated with dreaming here. (Note: Initial Stage One sleep should not be confused with Emergent Stage One Sleep. They are similar in some respects, but not the same.) STAGE TWO: This begins soon after falling asleep and marks the onset of the deeper stages of sleep. Sleepwalking and sleeptalking are usually associated with this stage. EEG patterns are distinct, marked by short bursts of waves. While a whisper might abruptly awaken the Stage Two sleeper, he may sleep peacefully through a loud ruckus. STAGE THREE: Stronger electrical impulses from the brain noted on EEG. (during waking state we normally have about 60 microvolts of electrical activity in the brain whereas in Stage Three a power of 300 microvolts has been recorded.) It takes considerable effort to awaken the dreamer. Temperature falls, breathing is slow and regular, heart rate slows even more. STAGE FOUR: Deepest sleep level. Large, slow EEG waves are similar to brain activity during a coma. Although eye movement is recorded and nightmares sometimes occur during this stage, stage four is usually associated with "dreamless sleep". EMERGENT STAGE ONE: This is where dreaming occurs (REM). Brain temperature rises, heart rate and blood pressure fluctutate, breathing is irregular, high oxygen consumption in the brain, rapid eye movement very apparant under the closed lids of the sleeper yet the body is very still with no turning over in bed, EEG patterns are similar to that of waking state. With each cycle of sleep, the length of time in the non-REM cycles decreases while the REM periods get increasingly longer as illustrated in the diagram below. There are fluctuations in the patterns between sleepers. There are also differences in any given individual from night to night and from stage to stage. R _90_mins_ __90_mins__ __90_mins_ ___90_mins__ Emergent E / _ \/ __ \/ ___ \/ ____ \ Stage I M / \ / \ / \ / \ _ _ _ _ _ _ _ _ _ | _ _ | | _ _ _| |_ _ _ _| |_ _ _ _ | _______ | | | | | | | | Stage II | N | | | | | | | | Stage III| o | | | | | | | \___ Stage IV | | | | | | \_/ | R | | | \__/ | E | \___/ ______| M \____/ Okay, that's a pretty rough sketch, but you get the general idea. As the amount of time spent in each non-REM stage decreases, the time spent in the REM stages increases, thus, the cycles remain roughly 90 minutes long. Clear as mud now? So how does this relate to the quality of sleep? Have you ever awakened feeling refreshed and certain that it's time to get up only to find that you've only been asleep for two or three hours? Have you ever had your full night's sleep but feel sleep-deprived all the next day? These are examples of how quality of sleep effect us. In the first case, it's safe to say that although you didn't sleep long, the quality of the sleep you did obtain was enough to leave you feeling refreshed (that's not to say that if you got up and stayed awake you wouldn't feel tired later in the day, though). The second example occurs when your quality of sleep was poor or 'bad'. If you do not experience your normal pattern of 90-minute sleep cycles, you can expect that your quality of sleep will be bad. Usually a 'bad night's sleep' is one where there are prolonged periods of Stage Two sleep and little to no Emergent Stage One sleep. In other words, you may have slept all night, but without sufficient REM, no amount of time asleep will be 'enough'. Alcohol, caffiene, nicotine, other drugs, certain medications, foods that cause indigestion, stress, anxiety, anticipation of something scheduled the next day, external stimuli, sleeping in unfamiliar surroundings, changes in exercise patterns (esp. exercising two or less hours before going to bed), and physical illness are examples of what can interfere with normal sleep patterns. Usually these interferences only effect the sleeper for a night or two. Sometimes, however, these alterations sleep occur over prolonged periods of time, in which case it may be necessary to make some changes in lifestyle such as avioding certain substances, reducing external stimuli or rescheduling exercise. If the problem persists the sleeper should, of course consult his or her physician. "Dream on. Dream about the world we're going to live in one fine day." -- The Oakridge Boys -- NEXT TIME: Improving Your Dream Recall and Keeping Your Dream Journal