The marshmallow test turned out to be a better predictor of SAT results  than the IQ tests given to the four-year-olds. The ability to wait for a  second marshmallow reveals a crucial talent of the rational brain. When  Mischel looked at why some four-year-olds were able to resist ringing  the bell, he found that it wasn't because they wanted the marshmallow  any less.  These kids also loved sweets. Instead, Mischel discovered,  the  patient children were better at using reason to control their  impulses. They were the kids who covered their eyes, or looked in the  other direction, or managed to shift their attention to something other  than the delicious marshmallow sitting right there. Rather than fixating  on the sweet treat, they got up from the table and looked for something  else to play with. It turned out that the same cognitive skills that allowed these kids to thwart temptation also allowed them to spend more  time on their homework. In both situations, the prefrontal cortex was  forced to exercise its cortical authority and inhibit the impulses that  got in the way of the goal.
Jonah Lehrer
How We Decide