How safe is it to drive when you haven鈥檛 had much sleep? Just like drinking alcohol, it turns out we鈥檙e not always a good judge of how mentally affected we are.
In an experiment where people were only allowed to sleep for just five hours a night, for a month, people did not realise that they had become less vigilant.
鈥淵ou鈥檙e asking the sleepy brain to tell us how well it is doing,鈥� says of Brigham and Women鈥檚 Hospital in Boston. 鈥淎nd the brain can鈥檛 always self-assess.鈥�
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Life in isolation
The finding emerged as part of a wider study to shed light on the question of what makes us less alert when we have gone without our normal amount of sleep: is it the lack of shut-eye itself or is it being awake for longer than normal?
Klerman鈥檚 team got seventeen volunteers to follow an artificial schedule based on a 20-hour day, by getting them to live in a windowless, sound-proofed room without phone, TV or internet.
Nine of the group had days that were about 15 hours long and nights of 5 hours; this meant their sleep was restricted without them having to be awake longer than normal. The rest acted as controls 鈥� to be a fair comparison they also had a 20-hour cycle, but with days of about 13 hours and nights of 7 hours, a similar ratio of wake-to-sleep that most of us get in a 24-hour day.
The sleep-deprived group did much worse than the rest on a test of alertness that involves watching a screen and pressing a button whenever a light randomly turns on. 鈥淭his is the equivalent of slamming on the brakes because there鈥檚 a kid in the road,鈥� says Klerman.
Unknowingly sleepy
The finding suggests it is lack of sleep rather than being awake for too long that makes us feel less alert. Klerman says that knowing this may help us design new drugs to help people whose work schedules mean they don鈥檛 get enough rest.
During the experiment, all the volunteers were asked to rate how alert they felt several times a day. Surprisingly, those who had been sleep deprived rated themselves as about as alert as those getting enough sleep.
of the University of Surrey, UK, says this is contrary to most people鈥檚 experience. 鈥淭he first thing you notice when you don鈥檛 get enough sleep is you feel sleepy.鈥�
But Klerman says that while people who say they feel sleepy are usually right, the problem is that people who don鈥檛 think they are sleepy can be wrong. 鈥淵ou can feel not sleepy and still be impaired. Isn鈥檛 that scary?鈥�
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