By Linda A. Bakos, RPSGT, Supervisor, Gaylord Sleep Services

“To sleep: perchance to dream.” Shakespeare, and poets through the ages, glorified the beautiful mystery of sleep. Still perceived as a quiet, simple phenomenon, sleep is an event that most enjoy. Sleep, however, is really quite complicated. The body’s physiologic systems use this time to conduct complex metabolic processes giving the body the chance to regroup in preparation for the challenges of the next day. In that preparation, the sleep state changes. Sleep has various components, each of which differs from the other. These components, called stages, affect the body’s ability to perform during the day.

Sleep researchers study the different stages of sleep through brain wave patterns recorded using an electroencephalogram (EEG). Brain waves are recorded through electrodes—small, metal disks connected to a long wire—placed on the head. Electrodes are also placed on the eyes to record rapid eye movement (REM) sleep and on the chin to help sleep researchers determine sleep stages.

Sleep consists of two main categories: non-rapid eye movement (NREM) sleep and REM. NREM is divided into four stages of sleep. Each is highly unique in how it looks, how long it lasts, and how deep it is.

• Stage 1 is the lightest stage of sleep. Considered transitional sleep, stage 1 moves people into a deeper and more rewarding sleep state. In most cases, people who are awakened after a couple of minutes in stage 1 would not have a sense that they had been sleeping. The EEG is low in height and often shows rolling eye movements. Most people spend only a few minutes in this stage. Stage 1 accounts for only 2% to 5% of the total amount of sleep time.

• Stage 2 comprises most of adult sleep, about 45% to 55% of total sleep time. Two unique features called K-complexes and sleep spindles easily identify this stage. A K-complex has a big upward spike and a big downward spike. A sleep spindle looks like a burst of very fast, scribbled spikes. People who are awakened during this stage would have the sense that they had been sleeping.

• Stage 3 is similar to stage 2 sleep, but the studies start to show large teepee-shaped EEG patterns called delta waves. Delta waves occur in small amounts and generally build up into the next stage of sleep, stage 4.

• Stage 4 is known by different names such as deep sleep and slow wave sleep because the EEG waves are slow and large. The EEG of someone in stage 4 looks as though there are teepees across the recording. This stage is also referred to as restorative sleep because it is the sleep that people need to feel good in the morning and perform during the day. Unfortunately, as we age the amount of time people spend in stage 3 and 4 sleep decreases. Children, as any parent will attest, have an overabundance of stage 4 since it is difficult to wake a sleeping child. Conversely, older adults often complain of not feeling refreshed in the morning. One reason is because their amount of stage 3 and 4 is minimal.

• REM sleep is where dreams develop. REM occurs about every 90 minutes at night. The telltale sign of the eyes moving underneath the eyelids characterizes REM sleep. The length of the REM period becomes longer as the night goes on. By the time morning dawns, people are generally in a long REM period. Most people experience dream recall after this long morning REM period.

REM has some very interesting features. Since the EEG looks like the teeth of a saw, the pattern is referred to as saw tooth waves. During this stage some researchers think that the rapid eye movements exhibited are the result of the brain studying its own activity. Another interesting feature during REM is the body’s ability to keep muscle activity quiet, which prevents people from acting out their dreams.

Sleep physicians use their knowledge of sleep stages to determine the quality of their patients’ sleep when they have a sleep study. It is important that the brain maintains a balance of sleep stages for everyday performance, thinking, creativity and peace of mind. For more information about sleep studies at Gaylord Hospital, contact mlopes@gaylord.org.

Gaylord conducts sleep studies at its facilities in Fairfield, New Haven, New London, Wallingford and West Hartford, Connecticut.

For more information on sleep and sleep disorders, check out the National Sleep Foundation's Web Site at www.sleepfoundation.org