Developed by Professor Walter Mischel, the "marshmallow test" is one of the world's simplest and most successful behavioural experiments.
In a study, he demonstrated that the longer a four-year-old child was able to wait before taking a sweet, the better were his or her chances of a happy and successful life.
Mischel has been monitoring the lives of dozens of his subjects since he began the marshmallow experiments at a nursery on the campus of Stan-ford University, California, in the 1960s.
His findings have proved so convincing that 40 of his original subjects, now in their forties, are preparing to undergo scans in the hope of answering a perplexing human question - why are some of us better than others at resisting temptation?
"Brain imaging provides a very exciting and important new tool," Times Online quoted Mischel, who now works at Columbia University in New York, as saying.
By studying the differences between the brains of subjects who turned out to be good at controlling their impulses and those who wolfed down the marshmallow the moment it was offered, researchers hope to come up with new ways of teaching the benefits of delayed gratification.