The researchers also tracked activity in the nucleus accumbens, a part of the brain involved in the processing of rewards. They observed elevated activity in the nucleus accumbens when a subject's rank within the group increased. "That shows that the task was motivationally important to people," Quartz says. "When they saw their rank go up, that was a reward."

Similar to the previous work on offering money for higher scores. Not very relevant to high-stakes testing, where people already have strong reason to want to succeed - and so have motivation.