36 | NewScientist | 17 April 2010

sco

tt

barb

ou

r/g

ett

y

Humans hate being cold, and for good reason: our long-limbed bodies are exquisitely adapted to lose heat, not to retain it. This makes perfect sense in the intense heat of the African savannah, where humans evolved. Without our technological adaptations to cold – clothing, heating, shelter – that’s where we’d all still be living, says Mike Tipton of the University of Portsmouth, UK, who studies human thermoregulation.

Surviving the cold is all about protecting core body temperature. This is usually

at 37 ̊ C, but it takes surprisingly little for it to start dropping. An ambient temperature of 20 ̊ C can induce hypothermia if conditions are wet and windy, says François Haman, a physiologist at the University of Ottawa, Canada.

When cold, the body starts to shiver and shuts down blood flow to the extremities. If core temperature falls by just 2 ̊ C, hypothermia sets in: first we start to lose consciousness, then the heart loses rhythm. Death follows at about 24 ̊ C, when

the heart stops. Usually.People have been known

to survive much lower core body temperatures. Anna Bagenholm survived the biggest drop ever recorded, to 13.7 ̊ C, when she fell into a part-frozen stream and became trapped under ice for 80 minutes.

The constant flow of icy water cooled her body to such an extent that by the time her breathing and heart had stopped, her brain needed very little oxygen in order to survive, giving her the chance of complete recovery. James Mitchell crow

KeeP COOl AnD CArry On

remembering an 11-digit telephone number is hard enough for most of us. yet one of the current record-holders for a feat of memory, Chao lu of China, was able to accurately recite 67,890 digits of pi from memory in 2005. But is that a mere drop in the ocean compared to the brain’s true capacity?

Our ability to absorb information is vast. In 1986 Thomas landauer, then at Bell Communications research in Morristown, new Jersey, looked at studies of how much visual and verbal information subjects stored while examining images and text, and how quickly they forgot it. This led him to estimate that the average adult stores around 125 megabytes of this type of information in their lifetime – enough to store the contents of 100 books the length of Moby Dick.

Accurately memorising a long string of digits in the correct order is a more demanding task than memorising ad hoc facts about a text or a picture. To discover the limit of the length of a single memory, it may be more informative to consider the techniques used by the memory champions.

Many of them use a mnemonic method. Before starting to memorise a number, they associate a person or object with each four-digit number from 0000 to 9999. The digits of pi can then be translated into a sequence of these people and objects, which the memoriser links by making up a story. This helps add interest to the random sequence of numbers and pegs down the memory.

lu takes roughly 1000 hours to memorise 40,000 digits. Assuming this rate would apply no matter how big the memory feat, someone who started memorising a number at the age of 20 and spent 12 hours a day at it, every day, would be able to remember around 8,760,000 digits by their 70th birthday. David robson

TOTAl reCAll

David Blaine starved himself for 44 days in a

glass box in London

100417_F_Extremes.indd 36 8/4/10 15:21:59