The electroencephalographic records from 43 subjects who slept for four consecutive nights in a laboratory environment were studied in an effort to describe the First Night Effect. These records showed that the first night of laboratory sleep contains more awake periods and less Stage I‐rapid eye movement sleep. There is a delay in the onset of Stages IV and I‐REM and the sleep is more changeable. These effects rapidly adapt out by the second night of sleep.

Electroencephalographically measured sleep of 80 healthy men and women between the ages of 50 and 60 years was measured for three nights. Compared with the sleep of a younger group of men and women (20 to 30 years), their sleep was characterized by more frequent and prolonged awakenings and shorter sleep stage periods. Older men displayed greater age-related changes than older women. There was an increase in the reliability of measures in the older persons across nights. When a modified scoring procedure for slow wave sleep based on frequency alone was used, the typically reported age decline was not found.

Age, length of prior wakefulness, length of time asleep, and a circadian influence all affect stage 4 sleep. The amount of stage 4 sleep decreases as subject's age increases and as time asleep increases. Longer periods of wakefulness before sleep result in greater amounts of stage 4 sleep in the first 3 hours of sleep. Sleep periods that begin at times other than the regular onset time tend to produce less stage 4 sleep; this decrease suggests a circadian effect.

Hypoxia is a well known cause of brain dysfunction. Neuropsychological impairments have been observed in normal subjects experiencing hypoxia iatrogenically as well as in patients with chronic lung disease. Recent investigations have demonstrated significant nocturnal hypoxia in subjects with sleep-disordered breathing. In the present study, heavy-snoring males, a group known to experience frequent episodes of sleep-disordered breathing received neuropsychological testing and a night of continuous monitoring of respiratory parameters. Partial correlations, controlling for age, weight, and education, indicated reliable relationships between nocturnal hypoxia and measures of general intelligence, verbal and nonverbal memory, and expressive verbal fluency. It is proposed that heavy-snoring males may potentially serve as a population in which to model the neurobehavioral effects of hypoxia. Further research in subjects with sleep-disordered breathing may help clarify the extent of the possible cognitive deficits as well as point out possible ameliorative treatments.

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