About 5 percent of these people endure psychological disturbances severe enough to merit treatment with medication or therapy, the researchers said.

"Polar madness can take a variety of shapes," Lawrence Palinkas, a University of Southern California anthropologist who wrote the paper in the Lancet medical journal along with Peter Suedfeld of the University of British Columbia in Canada, said in a telephone interview.

"Some people may have difficulty adjusting to the light-dark cycles, and so they can never get a decent night sleep and experience a sleep disorder," he said. "Some people can get clinically depressed. Some people just can't handle the confinement, with seeing the same people day in and day out for extended periods of time."

The researchers interviewed people on polar expeditions, reviewed diaries of early polar explorers and examined data from countries maintaining permanent polar research stations.

Apart from anecdotal reports of "polar madness" and cabin fever, they said, little was documented about the psychological demands that people on polar expeditions face as the work in frigid and dangerous conditions surrounded by the same small group of people and isolated from family and friends.

Depending on the time of year, these places can remain in darkness or light for months on end.

'DRIVE YOU CRAZY'

"Say there's somebody you go to lunch with and you don't notice the way that they eat. But if you ate with that same person day in and day out for six months, suddenly the way they chew their food is enough to drive you crazy," added Palinkas, who has ventured to the Antarctic seven times.

The Lancet paper detailed past cases of polar expeditions gone wrong, including an Arctic scientific expedition in the 1880s that descended into mutiny, lunacy, suicide and cannibalism, leaving only six survivors from a crew of 25 men.

Palinkas cited more recent examples of "polar madness" at research stations, including one staffer clubbing another with a claw hammer and another beating a co-worker with a pipe.

"There was a saying at the station for the remainder of the winter that 'If you've got a gripe, use a pipe,'" he said.

The researchers mentioned several other symptoms among people on polar expeditions such as memory impairment, anxiety, reduced alertness, headaches, boredom, fatigue, inattention to personal hygiene, intellectual inertia and over-eating.

In Antarctica, 20 nations operate 47 permanent stations for the entire year, with hundreds of people staying months on end. Arctic stations are operated by nations including the United States, Canada, Russia, Iceland, Sweden and Norway.

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