The next leap forward in understanding came when Aserinsky and Kleitman found rapid eye movements (REM) in 1953. In 1957 the REM were linked with dreaming. This defined sleep into two different observable states, REM sleep, and NREM (non-rapid eye movement or non-rem) sleep. Within NREM three different stages have been identified. These are defined by the different EEG patterns of electrical activity in the brain. They are measured by the height (amplitude) of the brain waves and frequency of up and down movement. There are also electrical changes occurring in the muscles (measured using an electro- myograph or EMG), and in movement of the eyeballs (measured using an electro-oculograph or EOG).
While awake the height is low and frequency fast. As we relax prior to sleep the EEG shifts to what are called alpha waves, at 8 to 12 cps (cycles per second). Stage one of sleep is the transition between this drowsy state of alpha waves to sleeping, in which theta waves occur, at 3 to 7 cps. In this first stage we experience random images and thoughts. This lasts about 10 minutes, followed by stage two, in which ‘sleep spindles’ occur which have 12 to 14 cps on the EEG. These last from 1/2 to 2 seconds, with K complexes following, which are slow large EEG waves. About half our sleep period is spent in this second stage of sleep. Deep sleep is reached when our brain exhibits delta waves, with 1/2 to 2 cps.
After approximately an hour and a half from falling into deep sleep, an exciting change occurs. We return to level two and REM occur. Suddenly the brain is alert and active, though the person is asleep and difficult to wake. This level has been called paradoxical sleep because of this fact. Voluntary muscular activity is suppressed and the body is essentially paralysed. Morrison has pointed out that, although the brain is transmitting full muscular activity messages, these are usually suppressed by an area of the brain in the pons. But bursts of short actions occur, such as rapid eyeball jerks, twitches of the muscles, changes in the size of the pupil, contractions in the middle ear, and erection of the penis. It may be that similar excitation occurs in the vagina. Also, autonomic storms’ occur dunng which large erratic changes occur in heart rate, blood pressure, breathing rate and in other autonomic nervous system functions. These are the changes accompanying our dreams.
If we slept for eight hours, a typical pattern would be to pass into delta sleep, stay there for about 70 to 90 minutes, then return to stage two and dream for about five minutes. We then move back into delta sleep, stay for a short period and shift back to level two, but without dreaming, then back into level three.
The next return to stage two is longer, almost an hour, with a period of dreaming lasting about 19 minutes, and also a short period of return to waking. There is only one short period of return to stage three sleep which occurs nearly four hours after falling asleep. From there on we remain in level two sleep, with three or four lengthening periods of dreaming, and returns to brief wakefulness.
The average amount of body shifting is once every 15 minutes.
1- In undergoing 205 hours of sleep deprivation, four healthy males showed various physiological and psychological changes. Some of these were headache, lack of concentration, hallucination, memory loss, tremor and, in some, paranoia. In all cases one night’s sleep restored normal functioning.
2- One in ten people who complain of excessive daytime drowsiness suffer from sleep apnoea, which is a stoppage of breathing while asleep.
3- A condition called narcolepsy causes sufferers to fall asleep at inappropriate times—while making love, walking, playing tennis, working.
4- As we age we usually sleep less. Our REM sleep in particular decreases sharply.