Reprinted with permission from the book DREAMING, SLEEPING & ESP
In the early 1900's researchers discovered that there was a connection between dreaming and "rapid eye movements" (REM). It was noted that (at certain periods of deep sleep) the eyes would burst into "twitches" which would then subside for a couple of minutes ... and then repeat.
Until recently, dream researchers never had a way to determine if a person was really asleep or not. A researcher would end the experiment by waking up the "subject" and asking if he/she was awake or not.
In the 1950's, researchers gained the tool they needed . . . they used a sensitive machine called an Electroencephalograph (EEG) to monitor activities of the brain in sleeping volunteers. Basically the EEG machine amplifies the electrical activity that occurs in the brain and causes it to operate a series of pens on "strips" of paper which corresponds to the electrical activity in the brain.
The EEG machine revealed that we produce different types of brain activity while we sleep . . . as the "sleeper" closes his eyes a fairly constant "pattern" occurs on the "strips" of paper at about 10 marks per second . . .
. . . These "marks" are called alpha waves.
As the "sleeper" becomes more drowsy the alpha waves disappear and a new pattern of marks appear which are less regular and occur at approximately 1 to 3 marks per second which are intermittently interrupted by sharp bursts of faster waves called "sleep spindles" ...
... this is called "slow wave" sleep.
After awhile the paper traces of the EEG machine shows another change in electrical activity . . . but this time the eyelids of the "sleeper" begin to twitch and flutter. This type of sleep is called REM sleep due to the rapid eye movements. The EEG machine showed electrical activity that was similar to the alpha waves. It was also discovered that rapid, irregular breathing also accompanies REM sleep --- (rates exceeding 18 breaths a minute).
It was found that people go through ninety minute (approx.) sessions of sleep which continues throughout the night.
These ninety minute sessions repeat themselves four to five times per night ... and during the periods of REM, vivid dreams occur which last approximately ten minutes.
Sometimes when "sleepers" were awakened during "slow wave" sleep, they would also indicate that they were dreaming.
While a sleeper may be difficult to arouse, the EEG (electroencephalograph) registers that the brain is alert and active.
It has been found that during REM sleep the dreamer does not sleep-walk because the arms, legs, and trunk of the body are temporarily paralyzed.