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.