The smell of chocolate sends brain waves "wild" and both distracts and relaxes people at the same time, experts said Tuesday.

No other smell tested on volunteers had such a strong effect, said Neil Martin, a neuropsychologist at London's Middlesex University."Chocolate was quite a star performer in this experiment," Martin said. "It seemed to make the brain go quite, scientifically, wild."

He added: "We found that they found it soothing and they found it pleasing and they found it very relaxing."

About 20 volunteers were asked to sniff artificial odors including chocolate, spearmint, almond, strawberry and garlic. In a second experiment, they smelled real odors, including chocolate again, baked beans, coffee and rotting pork.

They sat in specially designed smell-proof rooms, wore clouded goggles and had earplugs so they had to concentrate on the smells being presented to them, Martin told the annual meeting of the British Psychological Society.

Volunteers were not told what smells they were going to get.

While they sniffed, Martin's group measured their brain activity. Chocolate depressed brain waves known as theta waves, which are associated with attention, Martin said.

"This seems to be the one involved with attention. The more complex a task you do the more of this brain wave there is," he said in a telephone interview ahead of the conference.

Martin said it was not clear why chocolate alone should have such an effect.

"One reason is you are thinking about chocolate, maybe baking cakes or sweets, and because of that you don't pay much attention to your environment and it relaxes you," he said.

Or perhaps the emotional center of the brain somehow is being activated - but this would not explain why other pleasant odors did not have the same effect.

"The two odors you think might have been alerting - coffee and rotting meat - had no effect at all," he added.

Chocolate also increased alpha and beta brain wave activity, which Martin could not explain.

"Alpha is most commonly seen in a relaxed but waking adult, while beta is seen when people are doing something like mental arithmetic," he said.