Lance Kriegfeld is a professor of neurobiology at the University of California-Berkeley. He says the flight attendants did much worse. "They had a grossly reduced reaction time and percent correct on a relatively simple task."
In other words, their brains weren’t working as well. And not, says Kriegsfeld, because they were tired. Brain scans revealed that the brains of the jet-lagged workers were actually smaller.
Kriegsfeld was so intrigued by this study that he decided to replicate it, but this time using hamsters. Using artificial light, Kriegsfeld's shifted the hamster's day length by six hours. It was as if, he says, the hamsters had flown to Paris. Only instead, they got dissected.
Kriegsfeld paper -- published earlier this month in the scientific journal PLoS One -- involves a part of the brain called the hippocampus, which is critical for learning and memory. When he looked at this tissue in hamsters, he found that the jet-lagged hamsters had half as many new brain cells as they should have had.
Charles Czeisler, a sleep expert at Harvard Medical School, says that to understand the ways that jet lag affects humans, it's helpful to look back to an experiment done in 1729, by a French astronomer named Jean Jacques Ortous de Mairan.
At the time, says Czeisler, scientists were interested in why certain plants closed their leaves at night, and then opened them up in the day. What aspect of the sun were the plants responding to?
To answer that question, de Marian took what must have then seemed like an odd approach: He put the plants in a dark closet.
"Lo and behold," says Czeisler, "the leaves of the plant opened, even though they had not been exposed to the sun that day."
The plants, it turned out, weren’t following the sun at all. They were following their own internal clocks. It’s called a circadian rhythm, and we humans have them too. Or rather, the clocks, you might say, have US.
"You have daily rhythms in reaction time," says UC Berkeley's Lance Kriegsfeld, "daily rhythms in cognitive function and concentration, daily rhythms in coordination and balance."
Our sense of balance, the timing of our digestion, and the rapidity of our reaction time – all these things, says Kriegsfeld, change over the course of the day. Try doing any of them at the wrong time of day, and we just won’t do them as well.
Which brings us back to jet lag.
"When we upset the apple cart," says Czeisler, "it's like an internal temporal chaos." Changing time zones is physically confusing, he says. Some parts of our body think it’s daytime, others think it’s night. Czeisler says it's as if the conductor of an orchestra has disappeared. "Suddenly, the orchestra sounds like cacophony."
The physical toll this takes has been documented not just in pilots and flight attendants, who move frequently between time zones, but in people who work night shifts. Studies put these people at higher risk of breast cancer, digestion and fertility problems.
Czeisler says there is evidence from animal studies that recurrent shifting of circadian rhythms decreases lifespan in those animals.
One way that airlines and other employers could help protect their employees would be to keep them on regular shifts, so that they are always waking and falling asleep at more or less the same time. Or, change shifts gradually, so that workers have time to adjust to a new schedule.
But so far, that’s a luxury Patrick Smith, the pilot, rarely gets. He says he knows the risks, but he loves his job.
"Once upon a time it took weeks to cross the ocean in a sailing ship," says Smith. "Now we can do it in a matter of hours -- traveling hundreds of miles per hour above the earth, in almost perfect safety. It’s remarkable.
When we fly airplanes we are literally transcending the world we evolved to live in. Smith says that's a trade off he's wiling to make.
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