Another example: Methamphetamine abuse decreases dopamine transporter activity and compromises mental function. The brain image at the top left is from a normal control. The striatum is brightly lit in red and yellow, indicating the presence of many dopamine transporters, which contrasts with the brain of a methamphetamine abuser (bottom left). But what does this mean functionally? The graphs on the right show the impact on motor and memory tasks of this methamphetamine-driven decrease in dopamine transporters. The magnitude of the decline in the amount of dopamine transporter binding correlates with the extent of motor and memory impairment.