In the largest laboratory-based sleep-study restriction experiment, researchers found while behavioral and alertness improves significantly after a night of recovery sleep, with more sleep generating more improvement, some impairments lingered even after the maximum dose of 10 hours in bed. Neurobehavioral impairments like low attention span and delayed reaction times accumulated when a person received less than four hours of sleep over a five-day period.
The study involved 159 adults, with a mean age of 30 years. After receiving two nights of 10 hours of sleep, 142 participants were restricted to four hours in bed, from 4 a.m. to 8 a.m., for five consecutive nights. Afterwards, they were allowed a night of recovery sleep, ranging from zero hours to 10 hours. Seventeen participants served as controls, spending 10 hours in bed for the duration of the testing.
“Recovery of alertness dimensions was remarkably dependent on the duration of the recovery time in bed,” David F. Dinges, Ph.D., principal investigator and director of the Unit for Experimental Psychiatry and chief of the Division of Sleep and Chronobiology at the University of Pennsylvania School of Medicine in Philadelphia, Pa., was quoted as saying. “However, the sleep restriction was severe enough that recovery of alertness was not complete following a single night of extended sleep, indicating a residual sleep debt remained.”
A previous study led by Dr. Dinges, revealed chronic sleep restriction of six hours or less for two weeks resulted in cognitive performance deficits comparable to up to two nights of total sleep deprivation.