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The Falling Asleep Process in Adolescents.

STUDY OBJECTIVES
To investigate the pre-sleep psychophysiological state and the arousal deactivation process across the sleep onset (SO) transition in adolescents.


METHODS
Data were collected from a laboratory overnight recording in 102 healthy adolescents (48 girls, 12-20 years old). Measures included pre-sleep self-reported cognitive/somatic arousal, and cortical electroencephalographic (EEG) and electrocardiographic activity across the SO transition.


RESULTS
Adolescent girls, compared with boys, reported higher pre-sleep cognitive activation (p=0.025) and took longer to fall asleep (p<0.05), as defined with polysomnography. Girls also showed a less smooth progression from wake to sleep compared with boys (p=0.022). In both sexes, heart rate (HR) dropped at a rate of ~0.52 beats per minute in the 5 min preceding SO, and continued to drop, at a slower rate, during the 5 min following SO (p<0.05). Older girls had a higher HR overall in the pre-sleep period and across SO, compared to younger girls and boys (p<0.05). The EEG showed a progressive cortical synchronization, with increases in Delta relative power and reductions in Alpha, Sigma, Beta1 and Beta2 relative powers (p<0.05) in the approach to sleep, in both sexes. Delta relative power was lower and Theta, Alpha and Sigma relative powers were higher in older compared to younger adolescents at bedtime and across SO (p<0.05).


CONCLUSIONS
Our findings show the dynamics of the cortical-cardiac de-arousing process across the SO transition in a non-clinical sample of healthy adolescents. Findings suggest a female-specific vulnerability to inefficient sleep initiation, which may contribute to their greater risk for developing insomnia.