The dopaminergic reward system is clearly reactive to the intensity of a reward. For example in an fMRI study by Brian Knutson, the nucleus accumbens was twice as activated in response to a promised reward of five dollars as to a reward of one dollar. However, this system does not process the probability of a reward, how likely it is for this reward to actually occur. This lack of discrimination between low-probability and high-probability rewards can explain our attraction to lottery tickets. Why does the purchase of lottery tickets skyrocket when the prize money hits the millions? Because, even though the intensity of the reward stimulates our dopaminergic reward system, the low probability of winning does not register. To the extent that our frontal lobe does process probability information, our reward system may overpower it.