Brain 'holds key to body clock'

If you are planning to go on a longhaul flight, keeping cool could be enough to overcome jet lag.

Scientists have discovered that human biological clocks are driven by temperature changes in the brain, as well as changes in light.

Erik Herzog, of Washington University in St Louis, has already tested his theory on mice and found that adjusting the temperature of their brain fools their body clock.

Normally, brain temperature fluctuates by about 1.5C every day. The brain is at its minimum temperature at daybreak, and its maximum at midday.

This fluctuation exists even if without light. If you lived in a cave and never went out you'd still have a daily rhythm based on temperature," Dr Herzog explained,

In humans, as with all mammals, our body clock is controlled by the suprachiasmatic nucleus (SCN), located above the roof of the mouth.

Dr Herzog managed to grow a mouse SCN in a lab, and by warming and cooling it, fooled it into thinking it was a different time of day.

"We can, for the first time, effectively tell it what time we want it to think it is, and make that change almost instantly," he said.

Cooling the SCN made the mouse believe it was early morning, while increasing the temperature fooled the mouse into thinking it was midday.

It is hoped Dr Herzog's research could lead to a method of controlling our own body clocks. It would not just help long-suffering, long-haul travellers but shift workers as well.

Currently, it appears that getting plenty of sleep on a flight arriving at dawn may be the best way to avoid jet lag, as the brain will be at its coolest and will adapt quickly to a new day in the new time zone.

"Taking an early-morning jog on arrival is also likely to raise brain temperature quickly, warning the brain of the new time zone and telling it to wake up ready for a day's work,î added Dr Herzog.

His research - funded by America's National Institute of Mental Health - also disproved the bizarre theory, put forward in 1998, that shining light on the backs of the knees would beat jet lag.

The idea was that, by sensing light at the appropriate time, people could become synchronised to a new time zone.

But Dr Herzog said: "We took the SCN out of the animal, put it in a dish, and exposed it to light at night and dark during the day. It didn't change at all.î

He added that the human brain, while more sophisticated, could be affected by bursts of physical activity, fever or a small dose of aspirin or melatonin - a drug already used to lessen the effects of jet lag.

He said he hoped future research would find out exactly what caused these changes and unlock the secret of overcoming jet lag.

Doctors sounded a word of caution and warned that simply lowering human body temperature could be dangerous.

Eric Asher, the joint head of medicine at London's Third Space travel clinic, said: "This is amazing research but the problem is that our SCN is right in the middle of the brain, and cooling that down is very difficult without inducing hypothermia.

"Perhaps you could argue that, by giving yourself hypothermia, you're no longer worried about jet lag but it's really not something I'd recommend. But this is a first step, and we may be able to find a way around the problem."