The exact function of sleep is one of the big unsolved questions of behavioral biology, and sleep is in all cases essential, says Dutch scientist Serge Daan.

The 66-year-old scientist will receive the prestigious International Prize for Biology 2006 from Japanese Emperor Akihito next Monday, his university in Groningen said.

Daan will receive the award from the Japan Society for the Promotion of Science for his work in the field of chronobiology and behavioral biology.

"Timing of behaviour, that is how you could summarise my work," Daan said.

"It is the way animals and humans organise their time over different activities. I look at the influence of seasons and day and night rhythms."

Currently, he is a professor at the University of Groningen, the northern Netherlands, after having worked in Germany.

"The exact function of sleep is one of the big unsolved questions of behavioral biology. Sleep is in all cases essential.

"A rat which is kept awake all the time will die after one month," Daan added.

Apparently a process of reparation takes place in brains, but scientists are still searching for which way and why this takes place.

"During the time one is sleeping other important things can be done, such as maintenance and repair of the body. That's quite handy.

"A car you repair itself as well when it's in the garage and not while it is being driven," Daan added.

The Dutch scientist is delighted to meet the emperor, who will be present at the awards ceremony, and hopes to have the opportunity to chat with him about one of the emperor's favorite pastimes. He is said to have a laboratory at the Imperial Palace, collecting fish.

Daan earlier received the Hasselblad Award and the Alexander von Humboldt Forschungspreis for his research.