Submitted on May 1, 2006
Accepted on July 15, 2006
The adolescent decline of NREM delta, an indicator of brain maturation, is linked to age and sex but not to pubertal stage
Irwin Feinberg1, Lisa M Higgins1, Wong Yu Khaw1, and Ian G Campbell1*
1 Psychiatry, University of California, Davis, Davis, California, United States
* To whom correspondence should be addressed. E-mail: igcampbell{at}ucdavis.edu.
Two dramatic phenomena of human adolescence are sexual maturation and a steep decline in the delta EEG of non-rapid eye movement (NREM) sleep. It has long been speculated that these developmental changes are causally related. Here we present the first longitudinal data on this issue. Cohorts of 9 and 12 year old children (N=31, 38) were studied with in-home sleep EEG recordings at 6 month intervals over two years. Pubertal (Tanner) stage, height and weight were obtained at each time point. NREM delta power density (DPD) did not change significantly over ages 9-11 years, and its level did not differ in boys and girls. DPD declined by 25% between ages 12-14 years. This decline was parallel in the two sexes, but levels were lower in girls, suggesting that their DPD decline began earlier. Mixed effect analyses demonstrated that DPD was strongly related to age with Tanner stage, height, weight and BMI controlled but that none of these measures of physical and sexual development was related to DPD with age controlled. NREM delta is the sleep EEG component homeostatically related to prior waking duration and the intensity of waking brain activity. We hypothesize that the DPD decline is caused by age-programmed synaptic pruning that decreases waking brain metabolic rate. This reduced rate would decrease the "substrate" for delta homeostasis. Whether or not this interpretation proves correct, these longitudinal data demonstrate that the delta decline in adolescence reflects brain processes that are not predicted by physical growth or sexual maturation.
