The impact of sleep on sustained attention

This weekend’s NY Times Magazine is all about health – everything from the toxicity of sugar to the question of whether cell phones cause cancer. One article that caught our eye (at least after a cup of morning coffee) asks “How little sleep can you get away with?

David Dinges, the head of the Sleep and Chronobiology Laboratory at the Hospital at the University of Pennsylvania has asked just this question, and the answer is: you should really try to get 8 hours. Dinges’ 2003 study assigned dozens of subjects to three different groups: some slept four hours, others six hours and others, for the lucky control group, eight hours — for two weeks in the lab. The study used a measure called psychomotor vigilance task, or PVT. PVT is a “tedious but simple if you’ve been sleeping well. It measures the sustained attention that is vital for pilots, truck drivers, astronauts. Attention is also key for focusing during long meetings; for reading a paragraph just once, instead of five times; for driving a car. It takes the equivalent of only a two-second lapse for a driver to veer into oncoming traffic.”

The results?

Those who had eight hours of sleep hardly had any attention lapses and no cognitive declines over the 14 days of the study. What was interesting was that those in the four- and six-hour groups had P.V.T. results that declined steadily with almost each passing day. Though the four-hour subjects performed far worse, the six-hour group also consistently fell off-task. By the sixth day, 25 percent of the six-hour group was falling asleep at the computer. And at the end of the study, they were lapsing fives times as much as they did the first day.

The six-hour subjects fared no better — steadily declining over the two weeks — on a test of working memory in which they had to remember numbers and symbols and substitute one for the other. The same was true for an addition-subtraction task that measures speed and accuracy. All told, by the end of two weeks, the six-hour sleepers were as impaired as those who, in another Dinges study, had been sleep-deprived for 24 hours straight — the cognitive equivalent of being legally drunk.

These results are particularly interesting in light of a study recently published in the journal SLEEP that indicated that loss of an hour of sleep per night among children with ADHD had a significant impact on their ability to remain focused and sustain attention From a Science Daily article summarizing the research: “The study suggests that even moderate reductions in sleep duration can affect neurobehavioral functioning, which may have a negative impact on the academic performance of children with ADHD.”

Results of multivariate analyses of variance show that after mean nightly sleep loss of about 55 minutes for six nights, the performance of children with ADHD on a neurobehavioral test deteriorated from the subclinical range to the clinical range of inattention on four of six measures, including omission errors (missed targets) and reaction time. Children with ADHD generally committed more omission errors than controls. Although the performance of children in the control group also deteriorated after mean nightly sleep loss of 34 minutes for six nights, it did not reach a clinical level of inattention on any of the six measures.

Reut Gruber, PhD, assistant professor in the department of psychiatry at McGill University and director of the Attention, Behavior and Sleep Laboratory at Douglas Mental Health University Institute in Montreal, Québec, quoted in the Science Daily article, has advice for parents:

“The reduction in sleep duration in our study was modest and similar to the sleep deprivation that might occur in daily life,” Gruber said. “Thus, even small changes in dinner time, computer time, or staying up to do homework could result in poorer neurobehavioral functioning the following day and affect sustained attention and vigilance, which are essential for optimal academic performance.”

“An important implication of the present study is that investments in programs that aim to decrease sleep deprivation may lead to improvements in neurobehavioral functioning and academic performance,” she said.

I don’t know about you, but we’re going to go take a nap.

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