London: Munching a cheese sandwich is not just a tasty delight, but might also be a mantra to successfully negotiating that pay rise.

Psychologists at the University of Cambridge have revealed that cheese is a good source of the amino acid tryptophan, which is crucial to the manufacture of the brain chemical serotonin.

And, they say, people with high levels of this brain chemical have strong chances of succeeding in delicate negotiations affecting their own interests.

Revealing their observations during a study, the researchers revealed that the volunteers with low levels of serotonin were more likely to allow emotions rule their minds, and make decisions that harmed their long-term interests.

However, people with high levels of the chemical behaved in a more rational way, and put their own material advancement ahead of the short-term satisfaction of telling their boss exactly what they thought of them.