Part II : Clinical investigations in man

A. Normal subjects

We have carried out 20 records of sleep (from 10 p.m. to 6 a.m.) on six adult subjects (two men and four women, 20-35 years old) and three children (16 months, 22 months, 3 years). The EEG from the scalp was recorded continuously together with the movements of the eyes by means of electrodes placed in the vicinity of each eyeball. The EMG activity from the region of the back of the neck or from the external sternomastoid muscles, the EKG and the respiratory movements were also recorded with the EEG machine. The threshold of arousal was tested by auditory stimulation carried out by a loudspeaker triggered by a stimulator of variable voltage. During arousal produced in different stages of sleep, the subject was asked whether he remembered dreaming.

It is quickly apparent in these records that the EMG index is poor in man, at least with surface electrodes placed on the neck, since the EMG of both neck muscles and the sternomastoids disappear during the first stages of falling asleep, upon assuming the position of rest and sleep in man.

We shall adopt the terminology of Dement and Kleitman (1957a) on the subject of the different stages of sleep and we shall insist only on the phase of sleep characterized by rapid eye movements (REM).

Stage I is observed immediately upon falling asleep and may be very short in certain subjects. The threshold of arousal is very low. It is characterized by a low voltage relatively fast activity and an absolute absence of spindles or K-complexes. Slow pendular lateral movements of the eyes are observed at a frequency of about 10-20/min (Aserinsky and Kleitman 1955), and persist during the first three stages of sleep.

Stage II is characterized by the presence of spindle activity appearing on a back ground of fast activity and of low voltage. Sometimes theta activity may also appear. It is in this stage that K-complexes occur in the anterior and vertex regions.

Stage III is intermediate, characterized by the appearance of slow waves of high voltage associated with spindles.

Stage IV is characterized by the presence of diffuse delta waves of large amplitude, without spindles. During these last three stages the respiration is regular and slow and the heart rate decreases slowly.

The stage of sleep with REM. This stage has specific EEG and behavioral patterns which permit differentiation of it from the other stages of sleep (see Fig. 14 and 15). From the point of view of the EEG at the level of the occipItal. region, there are usually bursts or trains of alpha waves. These waves are often 1 or 2 c/sec slower than the waking frequency. The bursts of alpha waves are often "blocked" by REM. Besides these waves, the EEG is characterized by a low voltage activity without any rhythm. In some subjects, 20-25/sec waves are seen in the frontal region. There are no spindles or K-complexes spontaneously or induced by external stimuli. All these characteristics, however, may be observed during stage I of sleep.

But a very constant and specific activity is observed which permits a distinction between this stage of sleep and stage l ( Fig. 14). It consists of bursts of sharp waves, 2-3/sec in frequency. They have a triangular saw-tooth form and are rather narrowly localized to the central region. Their amplitude is maximal at the vertex, anterior parietal and anterior temporal leads. We have not observed them at the frontal or occipItal.regions.These waves occur in bursts of several seconds and usually immediately precede and sometimes overlap REM. They can last continuously, in some subjects, for some minutes. We have never observed such waves in other than the REM stage of sleep.

From the point of view of behavior, rapid eye movements during sleep have been described by Aserinsky and Kleitman (1955) and by Dement and Kleitman (1957a,b). They are very characteristic and constant and we have observed them in all subjects every night. We have found them in a 16-month-old baby and in a 3-year-old child who was blind since the age of one. These movements, bilateral and synchronous, with the eyelids half closed, are quite easily seen since the muscular tonus of the orbicularis decreases and the lids open enough to allow the white sclera to show. They resemble the scanning movements that might be executed by an awake subject while watching some activity taking place in his field of vision. These REM appear in clusters or bursts, but sometimes they may be almost continuous for some minutes. At the same time it is common to see discrete movements of the corners of the mouth and of the fingers. Respiratory variations are constant in all subjects: irregularity, decrease of amplitude and acceleration. It is not infrequent to observe a complete apneic pause at the beginning or at the end of the REM period of sleep.

The variability of the respiratory rate seems to be, together with REM, the best behavioral sign of this stage of sleep. The variations in rhythm of the heart are less constant. We have observed more often a slowing of the pulse. But in the same subject, during the same night, slowing, acceleration or no change may be observed during the REM period. This stage of sleep occurs periodically during the night ( Fig. 15), with a duration of 20-30 min. Usually the last period is the longest one. In adult subjects, the total duration is 20-25 per cent of the night's sleep. In children under 3, they represent 25-35 per cent of the duration of behavioral sleep. During this stage, the threshold of arousal by auditory stimuli is greatly augmented. We have found it 3 to 4 times higher than during stage II, 1.5-2 times higher than during stage III and IV ( Fig. 15).

REM periods and dream recall. We will discuss here only those dreams which could definitely be recalled by the subjects. Among 45 arousals during or immediately after a REM period, there were 31 reports of dreams (65%). On the contrary, among 40 arousals during stage I, II, III, or IV there were only three dream recalls (8%). This result confirms the findings of Dement and Kleitman (1957a, b) and strongly suggests that the REM stage of sleep signals the presence of dreaming in the human.

Next page