The modest sleep loss that results from going to bed an hour later than usual can compromise children's alertness and brain functioning, a new study suggests.

Previous studies of adults have found that sleep deprivation significantly impairs the brain's executive control system, which helps people organize, prioritize and focus on tasks. But few sleep-deprivation studies have focused on children, and those few have tended to examine extreme rather than modest sleep deprivation.

"The daily struggles between children and their parents usually occur at home and are often limited to modest changes in sleep," says author Avi Sadeh of the department of psychology at Tel Aviv University in Israel. "Persistent battles on topics such as 'just one more TV show' raise the scientific question: 'What difference does an hour make?'"

To help answer this question, Sadeh and colleagues studied the effects of adding or subtracting one hour of sleep on more than 75 children in fourth and sixth grades. For the first two nights of the five-night study period, the children adhered to their normal sleep pattern, and for the last three nights the children were asked either to extend or reduce their sleep time by one hour.

Children who got an extra hour of sleep actually experienced more night-wakings and a decreased percentage of sleep. Reducing sleep by one hour had the opposite effect: It resulted in decreased night-wakings and an increased percentage of sleep, the researchers found.

Previous researchers have identified these effects as the body's way of adapting to sleep loss, but in this study, the sleep-deprived children reported significantly higher fatigue ratings in the evening. In addition, their performance on several neurobehavioral tests compared unfavorably with the children who received an extra hour of sleep. The sleep-deprived children's performance on the reaction time test suffered, and their performance on the recall and responsiveness tests remained stable, while the children with the extra hour of sleep improved their performance on these tests.

The study results were published in the journal, Child Development.