A 2009 review in published in the journal "Child and Adolescent Psychiatric Clinics of North America" reveals that sleep quality changes across the life span. Yet the timing of rest and activity and the distribution of sleep and dreams exhibits a distinct pattern at each moment in time. A clear picture, therefore, of sleep and alertness at age 6 months can be documented.
Sleepiness
A 2008 study in "Sleep" shows that arousals from sleep decreased as infants aged from 2 to 9 months. This result suggests that children are gradually sleeping better during their first year of life. While this enhancement is occurring, the electrical activity of their brain is evolving as well. A 2007 report in the "Journal of Clinical Sleep Medicine" reveals that the dominant waking rhythm increased from 4 to 6 Hz. This finding indicates that the developing brain is getting better organized. Finally, a review in "Psychologie & Neuropsychiatrie du Vieillissement" notes that yawning appears by 3 months of age. That behavior makes it easier for a 6-month-old to stay awake.
Sleep Timing
Sleep and wake alternate in a daily rhythm. According to a 2000 investigation in "Clinical Endocrinology," this rhythm develops by age 2 months. That study also showed that the sleep-wake rhythm is tied to the cortisol rhythm. Cortisol is a steroid made by the adrenal gland. The production of cortisol rises during the day and falls at night. A 2007 experiment in the same journal looked at the latter rhythm in twins. Results indicate that such rhythms are determined more by the environment than by genetics.
Sleep Duration
As the sleep-wake rhythm becomes more prominent, sleep consolidates in the nighttime hours. A 2003 report in "Pediatrics" shows that the typical sleep duration at age 6 months was 14.2 hours. This number is down considerably from the amount of sleep at earlier ages. That change results from 6-month-old infants being less likely to sleep during the daytime hours.
Sleep Stages
Sleep also becomes more structured by 6 months of age. Repeating cycles of stages appear, and each stage becomes more well defined. According to a review in the "Journal of Clinical Sleep Medicine," the characteristics used to define Stage 2 and Stage 3 sleep became clear at this age. Stage 2 sleep is defined by sleep "spindles." Such spindles are brain waves oscillating at 14 Hz. These waves appeared in isolated brain areas which are not yet synchronized with each other. Stage 3 sleep is defined by "delta" sleep. These slow waves oscillate at 2 Hz.
Both sleep spindles and delta waves help keep the sleeping brain at rest. Each stage also has a unique role. Stage 3 is particularly important to the restorative function of sleep. That these stages are appearing in 6-month-old children suggests their rest is becoming more efficient.
Sleep Apnea
A discussion concerning the sleep of infants should include a warning about sudden infant death syndrome, or SIDS. According to "Baby Sake," SIDS is the leading cause of death in healthy infants between 1 and 12 months of age. While the cause of SIDS is unknown, breathing difficulties are often implicated. Sleep apnea is a momentary pause in breathing. Such a pause can lead to cardiac arrest and even death. According to "Science Direct," girls are more susceptible to apnea. The sleep of female infants, therefore, should be carefully monitored.
References
- "Child and Adolescent Psychiatric Clinics of North America"; Normal Sleep in Children and Adolescents; V. McLaughlin Crabtree et al.; October 2009
- "Sleep"; Maturation of Spontaneous Arousals in Healthy Infants; E. Montemitro et al.; Jan. 1, 2008
- "Journal of Clinical Sleep Medicine"; The Visual Scoring of Sleep and Arousal in Infants and Children; M. Grigg-Damberger et al.; Mar. 15, 2010
- "Psychologie & Neuropsychiatrie du Vieillissement"; Yawning; O. Walusinski; March 2006
- "Clinical Endocrinology"; Emergence of Salivary Cortisol Circadian Rhythm and Its Relationship to Sleep Activity in Preterm Infants; S. R. Antonini et al.; April 2000
