Development of Sleep in Infants and Children


Development of Sleep in Infants and Children




Sleep Onset


Sleep onset is not an isolated event. Identification of an exact moment of transition from wakefulness to sleep is difficult from both a behavioral and physiological perspective. For practical purposes, sleep onset can be correlated with certain behavioral and physiological changes occurring over a period of time. This time is, nonetheless, somewhat short. Behaviors typically associated with sleep include by are not limited to closed eyes, postural change, and behavioral quiescence. Additionally, there is modulation of responsiveness to auditory and visual stimuli, decrease in the ability of performance of simple tasks, and alterations in memory of events occurring several moments prior to sleep onset. EEG activity changes commonly associated with transitional sleep (N1) are not always perceived by the individual. Conversely, individuals may believe they have slept without obvious documentable changes in the EEG from the normal waking state.1


Dominant posterior rhythm (DPR) varies depending upon the child’s age and level of development. According to the Manual of Scoring Sleep Stages and Other Physiological Variables of Sleep,1a DPR shows only continuous slow irregular potential changes in infants less than 3 months of age. Activity attenuates with eye opening.



Wake


During wakefulness, DPR frequency in children less than 3 months of age ranged from 3.5 to 4.5 Hz. Frequency increases as the infant matures, reaching 5–6 Hz by 5–6 months of age, and 7–9 Hz by 3 years of age.


By 3–4 months post-gestational term infants, about 75% will have an irregular 50–100 microvolt, 3–4 Hz activity over the occipital region that attenuates with eye opening. Between 5–6 months of age many infants will demonstrate 50–110 microvolt activity over the occipital region at a frequency of about 5–6 Hz. This is apparent in about 70% of infants by 1-year post-gestational term. This pattern of continued and insistent increase in DPR frequency and amplitude continues so that by 3 years of age more than 80% of children have a mean occipital frequency of more than 7.5–9.5 Hz, 65% of 9-year-old children have an average frequency of 9 Hz, and by age 15 years this increases to about 10 Hz.


EEG amplitude is generally consistently greater than 50–110 microvolts. Average amplitude of the DPR during wakefulness is 50–56 microvolts in infants and children. About 10% of children have more than 100-microvolt activity between 6 and 9 years of age. Young children rarely exhibit EEG activity in the alpha range with voltage less than 30 microvolts.


Eye blinking might be seen with conjugate vertical eye movements that occur at a frequency of about 0.5–2 Hz. Chin muscle tone is high. Sucking movements may be noted and are characterized by extended rhythmic periods of increased chin muscle tone that appears to have a waxing and waning character. There may be conjugate irregular sharply peaked eye movements with an initial deflection lasting less than 500 milliseconds.



Transitional Sleep (N1)


From 2 to about 8 months of age, transitional sleep (N1) is characterized by a gradual appearance of diffuse 75–200 microvolts activity at a frequency of about 3–5 Hz. This amplitude is generally greater than that seen during wakefulness, and is usually 1–2 Hz slower than the waking background rhythm.


By 8 months to 3 years of age, generalized runs or bursts of semi-rhythmic bisynchronous 75–200 microvolts activity in the range of 3–4 Hz characterize N1. This is maximal over the occipital region. There may also be higher amplitude 4–6 Hz activity noted maximally over the frontocentral or central regions.


After 3 years of age, N1 is characterized by slowing of the DPR by about 1–2 Hz. The DPR can also be gradually replaced by relatively lower-voltage mixed-frequency activity. Beginning at about 5 years of age and progressing into adolescence, rhythmic anterior theta activity (RAT) can be seen. RAT is characterized by runs of 5–7 Hz moderate-voltage activity seen best over the frontal regions.


Monophasic negative broad sharp waves seen maximally over the central regions begin to be seen during N1 (and N2) sleep at about 6 months of age. By about 16 months of age, these vertex sharp waves of about 200 milliseconds in length can occur in bursts or runs and are most often seen during transitional sleep.


A distinctive paroxysmal EEG pattern of diffuse bisynchronous 75–350 microvolts, 3–4.5 Hz activity that occurs in bursts or runs maximum over the central, frontal, or frontocentral regions during drowsiness and during N1 sleep. This activity is termed hypnogogic hypersynchrony (HH). This pattern occurs early during sleep and disappears during N3 sleep. It is present in about 30% of 3-month-old infants and almost all children by 6–8 months of age. HH decreases in prevalence as development progresses and is identified in only about 10% of normal healthy children over 10 years of age. It is rare after 12 years of age.


At sleep onset, the electromyogram may reveal a gradual fall in muscle tone; however, this is not always present and a discrete fall in tone below that of wake may not be appreciated. Sucking movements can be seen during wakefulness and can be sustained throughout transitional sleep. Spontaneous eye closure typically signals drowsiness and wake-to-sleep transition. Slow conjugate sinusoidal eye movements replace rapid conjugate movements. Blinking disappears, and sustained eye closure is noted.



Stage N2 Sleep


Sleep spindles typically appear between 4 and 6 weeks of age. These rudimentary spindles are noted to be maximal over the central (vertex) regions and are typically of relatively lower amplitude and slightly lower frequency, but tend to remain about 12–14 Hz. Spindles in young infants can last longer than those typically seen in adults. More than three-quarters of children less than 13 years of age show two independent locations with different frequency ranges for sleep spindles. Spindles located over the frontal regions tend to range from 10 to 12.5 Hz and those over the central or centroparietal region range from 12.5 to 14.5 Hz. Frontal sleep spindles are more prominent than centroparietal spindles in young children but are abruptly decreased in EEG power and presence beginning at about age 13 years. Centroparietal spindles persist unchanged in presence or location as development continues.


K-complexes are well-defined waves characteristic of N2 sleep. These transient events consist of an initial negative sharp wave that is immediately followed by a positive wave lasting greater than or equal to 0.5 seconds. These events begin to appear as unique identifiable waveforms at about 5–6 months post term and are maximally located over the prefrontal and frontal regions.


Electrooculogram usually shows no eye movement activity. However, there may be frontal EEG artifact noted and slow sinusoidal eye movements may continue in some children. Chin muscle EMG is of variable amplitude, is typically lower than during wakefulness, and on occasion may be as low as during REM sleep.



Stage N3 Sleep


Slow-wave EEG activity during N3 sleep in the pediatric patient is typically very high voltage and can range from 100 to 400 microvolts. Frequency ranged from 0.5 to 2.0 Hz activity that is maximal over the frontal region. This slow-wave activity appears as early as 2 months of age, but most often between 3 and 4.5 months of age post term. Sleep spindles may continue during N3 sleep.


Eye movements are typically absent and there is often slow-wave EEG activity artifact noted in the electrooculogram. Chin muscle EMG is of variable amplitude and is often lower than in N2 sleep. Sometimes it can be as low as during REM sleep. In infants and younger children, sucking artifact may also be noted. N3 sleep is noted when 20% or more of a given 30-second epoch consists of slow-wave activity (in otherwise normal children), regardless of age.



Stage REM (R) Sleep


EEG during REM sleep in infants and children resembles that of adults. Nonetheless, the dominant frequency is slower and of higher voltage the younger the infant/child. Dominant R frequency tends to increase with age with 3 Hz activity at 7–8 weeks post term, 4–5 Hz activity with bursts of saw tooth waves at about 5 months of age, 4–6 Hz at 9 months of age, and prolonged runs or bursts of notched 5–7 Hz activity at 1–5 years of age. After 5 years of age, low-voltage mixed-frequency pattern of R sleep is quite similar to that of adults, although the amplitude may be somewhat higher.


Baseline chin muscle EMG is low and no higher than other stages of sleep. It is typically the nadir of activity noted throughout the recording. Irregular brief bursts of phasic muscle activity with duration less than 0.25 seconds can be superimposed on this low chin EMG tone. This phasic activity can occur in bursts and can be concomitant with similar bursts of rapid eye movements and anterior tibialis EMG twitches. Electrooculogram reveals irregular conjugate eye movements with a rapid initial deflection of signal lasting less than 500 milliseconds.


In small infants and young children, REM sleep is sometimes difficult to differentiate from wake or other sleep states. In these cases, utilization of other recorded variables to assist in state assignation is done. Respiration during NREM sleep is classically regular and monotonous with little variation. During REM sleep, considerable respiratory instability is noted. This is characterized by variation in rate, depth, minute ventilation, brief respiratory pauses, and brief episodes of increased respiratory rate.



Normal Course of Evolution of Sleep Across the Night



Healthy Children, Adolescents, and Young Adults


Normal, healthy pre-school-age children, school-age children, adolescents and young adults, transition into sleep through NREM sleep. This is in clear contrast to infants who normally transition to sleep through REM sleep. During transition, the posterior dominant EEG converts to an N1 pattern; theta activity appears; and eye movements become slow, rolling, and/or pendulous. EMG muscle tone changes little from waking levels. Arousal thresholds are low, but vary when meaning is assigned to a stimulus (e.g., a subject may respond to her/his name, but not to another name or a pure tone stimulus; often regardless of the amplitude which has been shown to be age-dependent). N1 sleep typically lasts briefly and is followed by transition to N2 sleep. Arousal thresholds are higher in N2 than in N1 and the same stimulus that may cause arousal or waking from N1 may cause a K-complex to appear in N2. After approximately 5 to 25 minutes of N2 sleep, there is a gradual increase in the appearance of high-voltage waves with a frequency ranging from 0.5 to 2 Hz. This is characteristic of N3 sleep, when comprising greater than 20–50% of the recording epoch. Arousal thresholds are considerably higher in N3 sleep when compared to other sleep stages. During the first cycle of the sleep period, N3 will last about 20 to 40 minutes and ends with a series of body movements and ascent to a lighter/higher NREM stage.


The first REM-sleep period of the night occurs about 70 to 110 minutes after sleep onset. The initial REM sleep period is often brief, lasting usually less than 10 minutes and is often missed during a single night of recording in the laboratory. Arousal threshold is variable during REM sleep and is generally considered to be similar to N2.


Subsequently, NREM and REM sleep cycle throughout the remainder of the sleep period at intervals of approximately 60 to 120 minutes. N3 sleep is most prominent during the early sleep period (first third to first half of the sleep period time) and propensity for N3 sleep decreases as the sleep period progresses. REM episodes, on the other hand, become longer and more intense throughout the sleep period, with the longest and most intense REM episode occurring in the early morning hours.


Though internal and external variability exists, volumes of sleep stages across sleep periods are relatively constant. N1 comprises 2–5%; N2, 45–55%; N3 sleep, 13–23%; and REM, approximately 20–25%. After the age of 5 years, proportions of sleep states remain remarkably constant throughout the remainder of the life cycle. Wake after sleep onset accounts for less than 5%. There are normally four to six cycles through various stages of sleep per night.



Newborns, Infants, and Young Children


Observation of newborns, infants, and children reveals that sleep occupies a major portion of their lives. A newborn infant spends more than 70% of every 24 hours sleeping. In contrast, adults spend 25–30% of their lives sleeping. Major ‘work’ of the waking child has been said to be play. Because sleep occupies such a large portion of a child’s life, the major ‘work’ of infancy and very early childhood is more likely sleep.


Behavioral and physiological characteristics of sleep in normal infants vary significantly from sleep in adults. Premature infants exhibit a lack of concordance between electrophysiological parameters and behavioral observations. This may also be true in some term infants.7,8 In newborn infants, electrophysiological characteristics of sleep and waking states in infants are often difficult since traditional characteristics cannot be fulfilled. Solutions to these problems have been suggested by a number of investigators. Prechtl and Beintema9 suggested state definition based on observable behaviors; Anders, Emdee, and Parmelee10 have suggested utilization of behavioral and polygraphic features; and Hoppenbrouwers11 suggested state definition based on polygraphic features, with observational criteria used only as supplemental information. Despite differences regarding state definition, it is clear that sleep in infants and children is significantly different than in older children, adolescents, and adults. Sleep, therefore, most likely performs a different function in the developing human.



Observations in the Fetus and Premature Infants


Rhythmic cycling of periods of activity and quiescence can be identified in the human fetus between 28 and 32 weeks’ gestation.7 Neither quiet (NREM) nor active (REM) sleep can be identified in premature babies between 24 and 26 weeks’ gestation.12 By 28 to 30 weeks, active sleep can be recognized by the presence of eye movements, body movements, and irregular respiratory activity. Chin muscle hypotonia is difficult to evaluate in the fetus and premature infant since there are few periods of tonic activity before 36 weeks’ gestation.7 Quiet sleep, on the other hand, cannot be clearly identified at this time and active sleep comprises most of the sleep period. Quiet sleep does not appear to emerge significantly until approximately 36 weeks’ gestation.7 Once identifiable, this state continues to increase in proportion regularly until it becomes the dominant state at approximately 3 months of postnatal life.


Spontaneous fetal movements can be identified between 10 weeks’ and 12 weeks’ gestation. Rhythmic cycling of quiescence and activity can be recorded in utero by 20 weeks.13 At 28 to 30 weeks, brief quiet periods appear, though their period is quite unstable.14 By 32 weeks’ gestational age, body movements are absent in 53% of 20-second epochs during 2- to 3-hour sleep recordings.7 ‘No movement epochs’ increase to 60% at term.


Patterns of physiological EEG activity become recognizable as early as 24 weeks’ gestation. Conflicting evidence exists concerning the independence of the maturation of sleep and the EEG with respect to intrauterine stage. Very young premature infants and full-term neonates have similar EEG patterns when compared at the same conceptional age. On the other hand, it has been shown that when a premature infant reaches 40 weeks’ conceptional age, she or he still has not attained a degree of EEG and CNS organization of a comparable full-term newborn.8 Premature infants show spindle development that is approximately 4 weeks in advance of that seen in full-term infants and a statistical difference between the length of quiet sleep in the term and premature infant exists, when measured at the same conceptual age.15 Some conflicting reports, however, may be secondary to definition and calculation of gestational age and conceptional age, or may be actual differences precipitated by development in an extrauterine environment significantly different from the normal intrauterine milieu. Extrauterine development of the premature infant occurs either in a 24-hour ‘light’ environment or a cycled light environment, rather than in the 24-hour ‘dark’ conditions of the uterus. In addition, other significant medical and developmental problems often exist in the significantly preterm newborn and continuous medical interventions are often required, disrupting the natural progression of sleep–wake cycle development. The effect of constant light and medical treatment regimens on the development of the nervous system and sleep cycling has not yet been elucidated.

< div class='tao-gold-member'>

Only gold members can continue reading. Log In or Register to continue

Related posts:

  1. Promoting Healthy Sleep Practices
  2. Cognitive and Behavioral Consequences of Obstructive Sleep Apnea
  3. Apnea of Prematurity
  4. Restless Legs Syndrome, Periodic Leg Movements and Periodic Limb Movement Disorder

Stay updated, free articles. Join our Telegram channel
Tags:
Jul 11, 2016 | Posted by in PEDIATRICS | Comments Off on Development of Sleep in Infants and Children

Full access? Get Clinical Tree
Get Clinical Tree app for offline access