Because dopamine is involved in the rewarding effects of drugs of abuse, it was hypothesized in this study that normal variation in the of number of dopamine receptors in a person’s brain could influence their response to drug exposure. To test this, human subjects were given the stimulant methylphenidate (Ritalin), their brains’ were imaged using PET, and they were asked whether they liked or disliked the drug’s effects. Those subjects who had high levels of dopamine receptors found the experience unpleasant, while those with lower levels of dopamine found it more pleasurable. This suggests that individual differences in a marker of dopamine function can influence an person’s susceptibility to continued drug abuse.
As a result of scientific research, we know that addiction is a disease that affects both brain and behavior.