The Sleep of Babies (1970)

The sleep of newborns has been considered to be a continuous and unchanging state between feedings. We wish to demonstrate two types of sleep in the newborn. An active sleep and a quiet sleep. One might well ask why behavioral scientists study the sleeping infant. The earliest modes of organizing neurophysiological events may determine and predict later modes of learning and perception. Maturation and a preparation for learning are taking place at a rapid rate in the infant. Both the overall organization of sleep-wake cycles and the minute behaviors during any one type of sleep may indicate these rapid maturational changes. You are watching the quiet sleep of a 4-day-old infant. What you see frequently confirms the commonly held belief that sleep is one unchanging state. A state of rest, inactivity, and replenishment. We wish to demonstrate in this film that quiet sleep is characterized by a different kind of activity. The electrical activity of the brain during quiet sleep is different from the electrical activity during active sleep. You will be seeing measurements of the brain's electrical activity later in the film. Respiration, which in infants is chiefly abdominal, is shallow and regular. One of the remarkable pieces of activity during quiet sleep is a sudden explosive motor discharge, which we have come to call a spontaneous motor discharge, or SMD. All of the babies that you will see are in a relatively quiet room just off the main nursery. The movements that you see are not elicited. The SMD that you are about to see occurs with its own autonomous rhythm every two to four minutes. This spontaneous motor discharge was filmed at 48 frames per second and is now shown at 24 frames per second in slow motion. The SMD is composed of a very early and fast flexor component. This is followed by a slower extensor component. The first component bears much resemblance to the startle response or the Pavlovian orienting response. The slower extensor component is much like the Moro response. The SMD at regular speed is so fast that it frequently is missed because of its occurrence during the eye blink of an observing adult. The frequency, shape, and intensity of this piece of behavior may prove to be an indicator of inner rates of maturational change. Active sleep is characterized by movements of the face, eyes, extremities, by an irregular respiration, and a different kind of electrical activity in the brain. Smiles, mouth-jaw movements, and rapid eye movements occur during active sleep. In boy babies, penile erections occur most frequently during active sleep. In observing infants, we have tried to develop behavioral categories accurate enough to allow rather complete description, but simple enough to be used by nearly anyone after some training. No piece of behavior fits categories exactly, and some behavior, such as a rapid eye movement, is hard to see on film because the film does not allow three-dimensional viewing. We are interested in developing a method for recording observable behavior while collecting neurophysiological data. One or two observers sit at a standardized distance from the infant and push keys on a keyboard coded for certain behaviors. Measurements of brain activity, rapid eye movements, and respiration are made concurrently during the 2-3 hour inter-feeding period. Some of the behaviors coded on the keyboard are a fine body movement defined as any movement across the body joint or joints, but limited to one extremity or the head. A gross body movement defined as any movement involving more than one extremity. A smile defined as the movement of one corner of the mouth pulling away from the midline and upward. This is the minimum requirement for a smile. A mouth jaw movement is the alternate tension and relaxation of muscles raising and lowering the jaw. All movements of the face, other than smile and mouth jaw, are put in the category of facial movements. Vocalization is defined as noise made by the infant forcing air across the voice box. We arbitrarily define cry as vocalization of a 3-second duration or greater. A shudder involves the very rapid alternating tension and relaxation of extremities. This clonic movement gives one the impression of a shiver. Rapid eye movements are noted by the quick rippling of the closed eyelid as the cornea passes beneath the lid. A key for eyes open is pressed only when the observer can see the pupil. Here you see a 4-day-old infant in active sleep. Note the irregular bumpy respiration. You will see an elegant fine movement of the right hand. >> This was accompanied by a movement of the left arm and would be coded as a gross body movement. Next is a gross followed by a smile. You will next be seeing a period of relative quietness punctuated by some fine movements of the leg and foot. A gross body movement will be followed by some minimal facial activity and then another gross with the shudder of both arms and hands. Watch the arms and hands with the next gross movement. The clonic character of that particular movement was so fast that it is uh hard to judge as a shudder. You will begin to see the rhythmic occurrence of gross body movement that seemingly sets off a sequence of behavior. After the next few gross body movements, watch the mouth and eyes for smiles, mouth jaw movements, and rapid eye movements. Again, you see a period of relative quietus. With bumpy respiration. And after the next quick gross movement, you will see a smile and some vigorous rapid eye movements. Smile followed by some mouth jaw movements. These bursts of rapid eye movements, smiles, mouth jaw, and penile erections seem to follow in the wake of a gross or shudder. We have wondered if competing centers catch the spark over and begin to lay down the framework for sequences of behavioral patternings. Again, you will see the rapid eye movements. And another gross body movement with the facial movement that we have come to call a cry face. After the next gross body movement, you will see a flurry of rapid eye movements accompanied by some fine movement of the wrist. >> This is another 4-day-old infant seen in the afternoon in her feeding period. You will see slow eye movements and a smile. Frequently, the rapid eye movements are superimposed on the slow turning of the eyes up into the head. Simple observation without the use of eye leads has given us many false negative and false positive reports of rapid eye movements. You will see two distinct smiles fulfilling our minimal definition. The stretch is partially defined by an arching of the back either in a convex or concave fashion. As the baby gets along into the afternoon, the time between stretches becomes shorter. Most frequently associated with a stretch which as you would expect, a yawn that we will freeze on the film. Vocalization, we find, is also closely associated with increasing arousal and increasingly frequent stretches. As the baby comes into the awake state or into crying. Here you are seeing the stretch. And you will next see a stretch associated with a yawn. This infant has been filmed in such a way that the action is speeded. Watch the minutes pass on the clock to get an impression of the degree of speeding. The purpose of this time-lapse filming is to better reveal overall pattern. Sleep has an organized pattern produced by the duration of each period of active or quiet sleep, by the amount, type, and vigor of activity, and by the transitions between types of sleep. Transitions may be gradual or abrupt. During normal speed viewing, changes take place so slowly that the pattern of sleep is difficult to appreciate. It is more easily appreciated if time is compressed by a film such as the one you are seeing now. A film such as this is obtained by shooting at one frame per second rather than the usual 24 frames per second. A normal 40-minute cycle from one period of active sleep to the next may be seen in less than 2 minutes. Film such as this may prove useful in comparing different infants. Despite its speed, the film allows observation of many details. Respiration can be seen clearly enough to allow some evaluation of its regularity. Eye movements may be quite obvious. Characteristic parts of the spontaneous motor discharge may even be seen during quiet sleep. The intensity and periodicity of bursts of movement during active sleep may be far more obvious in a film like this than during normal observation. By better showing overall pattern and by reducing observation time, this sort of film may allow comparisons to be made more efficiently and more effectively. >> Another method for recognizing the overall pattern of sleep is provided by the cumulative record. Long used in studies of learning and drugs, the cumulative record simply consists of a line moving up each time something occurs and moving to the right as time passes. Its slope shows rate. You are looking at a cumulative record of eye movements. It clearly shows periods of active sleep during which eye movements are frequent. It provides a partial idea of the intensity of the rapid eye movement period. That is to say, the more frequent the eye movements, the steeper the line. Cumulative recordings such as this have been found to provide a surprisingly accurate impression of the patterning caused by recurring periods of active sleep. Obtained automatically, such records would rapidly provide an immediate impression of how an infant was sleeping. Cumulative recordings supplement films which compress time. Whereas the film emphasizes observable behavior, a cumulative recording emphasizes physiological events. Both techniques reveal overall patterning. You've been looking at the record of a 3-day-old infant. This record is rather similar to other records of 3-day-olds. Records for 3-day-olds are clearly more steep than records of our 5-day-olds. They show other differences which may reflect increased organization of the pattern of sleep. This is part of a polygraph recording made continuously at a speed of 10 mm per second. The top channel is the electroencephalogram, a recording of the electrical discharge of the brain. It was obtained by a monopolar lead rather far back on the parietal bone near the occipital area. Below the EEG, you see a record of respiration made from a tiny elastic tube around the infant's abdomen. The two bottom channels show eye movements as well as the anterior temporal electroencephalogram. When the pens move synchronously and in the same direction. They are usually showing the electrical activity of the brain. These recordings were made during quiet sleep. The electroencephalogram of quiet sleep shows regular episodes of slower high amplitude waves. Respiration is fairly regular. Some of the electroencephalogram can be seen in the eye movement channels. A spontaneous motor discharge can be recognized on the polygraph recording. Its position is nearly equidistant between the groups of episodic slow waves. We wonder if there isn't a brain stem rhythm section. That is to say a pacemaker determining the periodicity of bursts of slow waves and occasionally causing a spontaneous motor discharge to come in exactly on beat. During active sleep episodic slow EEG waves are typically replaced by a lower more continuous EEG. Respiration changes from regular to an irregular pattern having apneic periods. Rapid eye movements cause the electroencephalogram pens to rapidly simultaneously come together or move apart. In a polygraph recording the differences between active and quiet sleep are often greater than the differences between sleep and wakefulness. This keyboard is connected by switches to pens on an Esterline Angus event recorder. In this way we can with training continuously observe the infant's behavior and obtain a write-out on event recorder paper driven at a standardized speed of 6 in per minute. The items of behavior such as a fine body movement, a yawn, or a stretch, or smile are printed above each key. Switching permits the recording of both continuous and discontinuous events. Deflections of the event recorder pens are synchronized with pens of the polygraph so that we obtain synchronized records of both behavioral and neurophysiological data. This particular keyboard is set up for simultaneous observation by two observers. A procedure that increases accuracy and allows study of agreement between observers. This frequency bar graph shows the behaviors listed along the left border. The 85-minute observation period is measured along the lower margin in 5-minute units. These are the behaviors of a normal 4-day-old female born at term. Mother had had a saddle block anesthetic. Observations were made in a relatively quiet room immediately after the 1:00 p.m. feeding. During the first 13 minutes, this baby does a good deal of mouth-jaw movements, fine body movements, gross, stretches, and rapid eye movements. There are no sudden motor discharges. At this stage in our research, we were not recording rapid eye movements, but making the gross observations. The respiration is irregular for the first 17 minutes. This cluster of events during the first 13 minutes is called active or REM sleep as opposed to the next type, which is called quiet sleep. Quiet sleep shows itself by the infrequency of movements except for isolated fine and gross body movements. The SMDs appear rhythmically and are frequently followed by the gross body movements. Respiration is regular and shallow. The change in respiration lags behind behavioral changes and the slanted lines at the top of the graph represent a period of transition from one type of sleep to the other. The graph demonstrates the alternating nature of two distinct types of sleep in the 4-day-old infant. In summary, we have demonstrated the methods we are using to describe two types of sleep. This description can be done by behavioral observations recorded on charts and films and by electrophysiological data recorded on polygraph paper and the cumulative records of rapid eye movements. Slow-motion films, given frame-by-frame study, show the details of particular movements. The details of minute-to-minute changes are demonstrated by direct observation and by continuous physiological recording. However, the overall pattern of sleep can be better appreciated from cumulative records of eye movements and time-lapse films. Both particular movements and the overall pattern of sleep seem likely to provide indicators of development giving a better answer to the question "How is my baby getting along?"