WASHINGTON U.S. researchers have discovered that the back of the knee, of all places, can be used to help control the biological clock of human beings. By applying light to the backs of the knees of 15 human guinea pigs for several hours at a time, and at different times of the day or night, scientists were able to adjust their need to sleep and wake either forwards or backwards.

This would mean, for example, that jet lag would be easier to overcome than had previously been thought. The experiment is detailed by scientists Scott Campbell and Patricia Murphy of the Cornell University Laboratory for Chronobiology in White Plains, New York in the U.S. professional journal Science. All that had been known previously was that photoreceptors in the eyes were linked to a person's body clock, the circadian rhythm of a human being.

Measurements of body temperature and the level of the sleep hormone melatonin in the body confirmed that the backs of the knees can alter biological rhythm just as effectively as the eyes - and independently of the eyes. Beams of light were played on the backs of the knees for three hours at a time, whilst the test subjects were asleep.

This means, deduce Campbell and Murphy, that sleep disturbance can be relieved, even in sleep. The recipe could help travellers who have crossed several time zones, as well as shift workers and older people with sleep problems. Yet Campbell and Murphy were unable to explain the mechanism behind this. They suspect that parts of the blood act as photo receptors and speed up melatonin production, or where there is light, slow it down.

Studies of the fruit fly drosophila only recently revealed that this insect can adapt its inner clock through autonomous receptors on its body and wings. (DPA)