Phase advance in moderately sleepy and alert normals.

Phase advanced sleep (by 4 hours) was studied in 28 healthy, normal men and women, aged 21-50 years, without nocturnal sleep or daytime sleepiness complaints. Eleven subjects (6 men and 5 women) with moderately short (< or = 10 minutes) average daily sleep latencies on the multiple sleep latency test (MSLT) were compared to 17 (11 men and 6 women) with relatively long (> or = 12 minutes) latencies. Nocturnal sleep on both a baseline and a shift night differed between the groups. The moderately "sleepy" group had shorter sleep latencies and less wakefulness during sleep than the moderately "alert" group. The phase advanced sleep schedule reduced sleep efficiency in both groups, but the moderately sleepy group showed a lessened effect of the shift. Additionally, sleep efficiency was reduced in the moderately sleepy group only during the first 2 hours of the sleep period, while sleep efficiency was uniformly disturbed in the moderately alert group throughout the night during the phase advance.