Sleep patterns in the young adult are the most studied and best defined, and commonly serve as the basis with which the sleep patterns of other age groups are compared. Normal healthy young adults exhibit a predictable and well-characterized pattern of alternating cycles of rapid eye movement (REM) and non-REM (NREM) sleep across a typical night of sleep. Each cycle lasts 90 to 120 minutes, with 4 to 6 cycles expected across a night of sleep. The initial cycle is usually slightly shorter and they become longer as the night progresses. With the initial descent into sleep, a few minutes of light sleep (N1) is initially seen, followed by deeper stages of sleep (N2, N3). Usually there are 10 to 25 minutes of N2 sleep followed by increasing delta activity leading into N3, the deepest stage of sleep. After approximately 90 minutes of sleep, there usually are a few minutes of lighter sleep (stage N2 or N1) followed by the development of REM sleep. The first period of REM sleep is usually the shortest (<5 minutes) and often has only subtle rapid eye movements that make it more difficult to identify.

Deeper sleep (N3) is primarily seen in the first 2 sleep cycles, and often is the dominant sleep stage early in the night. With each sleep cycle, the REM duration usually increases and the later portion of the night is spent alternating between stage N2 and REM. During a typical night sleep, a young adult spends 75% to 80% in NREM and 20% to 25% in REM sleep. NREM sleep is usually divided into stage N1 (2%–5% of total sleep time [TST]), N2 (45%–55% of TST), and N3 (18%–23% of TST).^1–4

Development of organized sleep/wake states and subsequent evolution to a circadian sleep/wake cycle is a major developmental accomplishment of a neonate. Age-appropriate sleep ontogeny is a sensitive marker of central nervous system development in this age group. As opposed to the well-defined sleep pattern of the young adult, infants have cycles composed of quiet sleep, active sleep (the physiologic precursor of REM sleep), and wakefulness. Cycle duration is variable, in the range 50 to 300 minutes, and the initial descent into sleep is most commonly into active sleep. The EEG/polygraphic characteristics of these sleep stages are discussed later. By age 3 months, infants start to develop a circadian rhythm and, by age 4 months, sleep is usually concentrated during the nighttime hours.^1,4,5

There are more limited studies of sleep/wake changes in this age group. During the first 2 to 3 years, sleep becomes consolidated in a long nocturnal sleep period, usually about 10 to 12 hours in duration. Typically, the child initially has two naps, a short one in the morning and a longer one in the afternoon. Gradually the morning nap is abandoned and then, usually by age 4 to 5 years, sleep is consolidated into a single nocturnal sleep period. At age 1 year, REM sleep occupies approximately 33% of TST. This proportion decreases to the adult value (20%–25%) by about age 4 to 5 years. Initially, the sleep cycle duration is about 60 minutes, but lengthens to the adult value (90 minutes) by about age 5 years. Between the ages of 5 and 10 years, less prominent changes are noted. During these years, the single nocturnal sleep period shortens to 9.5 to 11 hours, the percentage of N3 sleep decreases modestly, and naps are unusual.⁶

Several changes occur in sleep in older adults. These changes include increased nocturnal arousals and awakenings, decreased sleep efficiency, a mild increase in stage N1, marked decrease in stage N3, and relative preservation of REM sleep. As a result of these factors, the elderly typically require more time in bed to obtain their usual 7 to 8 hours of sleep. The latency to the first appearance of REM sleep decreases and the amount of REM sleep is distributed more uniformly across the night; both patterns are also seen in depression. The amplitude, duration, and occurrence of sleep spindle activity decrease, and there is a loss of the consolidation of sleep in the nocturnal period with more wakefulness during the night and more frequent naps during the day.

As noted earlier, one of the biggest changes in sleep in the elderly is the decrease in stage N3 sleep. Healthy elderly without primary sleep problems spend less than 10% of their TST in N3, compared with 25% to 35% in young adults. Older adults had an average of 27 arousals per hour of sleep compared with young adults who averaged 10 per hour of sleep. Sleep efficiency (TST/time in bed) in older adults is typically around 80% compared with young adults who average greater than 90%. Older healthy adults average 18% of REM sleep time compared with 20% to 25% in younger adults.^1–35 Sleep among elders is characterized by increased number and duration of awakenings, decreased sleep efficiency, with an increase in wake time after sleep onset.

A recently published meta-analysis studied age-related changes in sleep architecture among 65 studies of all-night polysomnography (PSG) or actigraphy done on 3577 healthy subjects, aged 5 years to 102 years.⁵ The results of this study, summarized here, reinforce many of the observations outlined earlier. With increasing age, there is a gradual reduction in the TST. However, this trend in school-aged children was present only with recordings during school nights, suggesting that the reduction in TST during school-age years reflects externally imposed sleep restrictions. There is a small but significant increase in sleep latency (the time an individual takes to fall asleep) of about 10 minutes from age 20 to 80 years. The percentage of stage N1 sleep increases during adulthood, likely reflecting greater sleep disruption. From ages 5 to 60 years, there is a significant increase in the percentage of stage N2 sleep, which is likely caused by the marked decrease of stage N3 sleep. Infants may spend 50% of TST in REM sleep and, by age 4 to 5 years, the percentage of TST spent in REM approaches the adult values of 20% to 25%. The latency of REM sleep increases with age. Neonates preferentially enter active sleep (the precursor of REM sleep). By the age of 6 months, an infant immediately enters REM sleep approximately 20% of the time. By age 2 years, sleep-onset REM sleep is rare and the usual latency to REM sleep is 60 minutes. The percentage of TST spent in stage N3 or slow wave sleep decreases with increasing age. In young children, stage N3 sleep can account for 40% of TST and usually reduces to 15% to 25% by the teenage years.⁵

During this early stage of life, the EEG can be divided into wakefulness, active sleep, and quiet sleep.

Wakefulness and active sleep

In the term neonate, similar EEG patterns are seen in both wakefulness and active sleep. Active sleep is usually characterized by a low-voltage irregular pattern, with continuous 25 to 50 μV theta and less than 25 μV lower-amplitude delta activity. A second pattern is sometimes seen in the initial descent into sleep and is termed a mixed pattern, which is similar to the low-voltage pattern described earlier but has higher-amplitude delta activity (Fig. 1). Differentiating wakefulness from active sleep in a neonate is not possible from EEG patterns alone. Active sleep, considered to be the precursor of adult REM sleep, characteristically has irregular respiration, increased heart rate variability, and frequent body and eye movements.^7,8 The loss of muscle tone is less consistently identified than in adult REM sleep and often the technologist’s report of the patient’s eyes being closed is the strongest confirmation of sleep state.

Fig. 1 Active sleep is seen in this term infant with low-voltage theta and delta activity and rapid eye movements seen in the eye leads (FP1, FP2, ROC, and LOC). The EMG shows reduced activity.

(Courtesy of Aatif Husain, MD.)

Quiet sleep

Two patterns are seen during quiet sleep in the term infant: trace alternant and high-voltage slow. The trace alternant pattern can be seen from birth up to 46 weeks’ gestational age and is characterized by symmetric bursts of delta activity (50–300 μV) lasting a few seconds with a similar duration of lower-amplitude mixed frequencies (25–50 μV). By 44 weeks’ gestational age, the EEG of quiet sleep predominantly shows the high-voltage slow pattern with high-voltage (50–200 μV) theta and delta activity (Fig. 2).^7,8

Fig. 2 Quiet sleep is seen in this term infant with high-voltage theta and delta activity.

(Courtesy of Aatif Husain, MD.)

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

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Yield of Sleep and Sleep Deprivation on the EEG in Epilepsy
2. to Seizures, Epilepsies, and Epilepsy Syndromes
3. of Central Pattern Generators with Parasomnias and Sleep-Related Epileptic Seizures
4. Unexpected Death in Epilepsy: What Does Sleep Have to Do With It?

Stay updated, free articles. Join our Telegram channel

Join