The steep decline in the adolescent years of the intensity of delta brain waves during slow-wave sleep begins earlier in girls than in boys, according to a study published in the May 1 issue of the journal Sleep.
The data compiled from all-night electroencephalogram (EEG) recordings show that the intensity of delta waves in non-rapid-eye-movement (NREM) slow-wave sleep is 37 percent higher in 12-year-old boys than in girls of the same age. Consistent data were obtained in two separate sets of recordings conducted six months apart.
These are unexpected findings for Ian G. Campbell, PhD, of the University of California, Davis, and his colleagues, who anticipated that the children in their study would show no gender-based differences in their EEGs during slow-wave sleep.
“Although there are well-known sex differences in other aspects of maturation, the literature does not suggest the presence of a sex difference in the EEG at this age,” said Dr. Campbell. “Therefore, we did not expect to find one. We were surprised that such a robust difference appeared at this early age.”
The intensity of slow-wave EEG readings peaks in early childhood, according to background information in the article. It then decreases until about the fifth decade of life, making its steepest decline in the adolescent years.
The researchers hypothesize that the decrease in slow-wave EEG during adolescence is but one component of a widespread brain maturation process. They suggest that further results from their ongoing four-year study will help determine if the sex difference in delta EEG is a result of brain maturation or other independent factors.
According to the authors, current theory holds that the intensity of delta waves in slow-wave sleep plays a vital role in helping the brain recuperate from the effects of waking activity.
The researchers write that their findings likely reflect a difference between males and females regarding the need for the recuperative processes of sleep. Furthermore, they believe that their study of the normal process of adolescent brain maturation may hold clues to the understanding of how mental illnesses develop.
“One long-standing puzzle in the etiology of major mental illnesses is that they often emerge during adolescence,” said Dr. Campbell. “It is possible that the normal, pervasive brain changes during adolescence may sometimes contain errors that give rise to these illnesses.”
The study utilized portable monitoring devices to perform EEG recordings for four consecutive nights as participants slept at home.
The researchers are following a study group of children with recordings every six months for a period of four years. The study group is made up of 32 nine-year-olds and 38 12-year-olds, with equal numbers of boys and girls at both ages.
The report published in SLEEP is based on measurements from the first two semi-annual sleep recordings. Data from 10 subjects of each age-sex group with the most reliable EEG recordings were selected for comparison.
The study is being supported by a grant from the National Institutes of Health.
The journal Sleep is the official publication of the Associated Professional Sleep Societies, LLC, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society.