MAO is an enzyme that is significant in regulation of neurotransmitter including Norepinephrine. As we know, the level of Epinephrine has a relationship with the activated rewarding centers in brain, since one of the properties in sensation seeking individuals is low levels of MAO in them. The level of Noreoinephrin in them tends to be high, and the rewarding centers in them are ready to be active. It means that those who have high sensation seeking, will experience more pleasure or receive more rewards if they take drugs such as Cocaine that excites the rewarding centers in brain. Therefore, individuals with high sensation seeking will use the drug again. On the contrary, individuals with low sensation seeking will not experience the same level of rewarding at the time of taking drugs due to difference in their brains' chemistry, so there is low probability to take it again. In answering the question of where the differences of available differences in the level of MAO are caused, Zuckerman believes that these differences are hereditary (Zuckerman, 2000).