Doctors usually identify the disorder in children.But experts say the behaviors often last into adulthood.Researchers have been looking for the cause or causes of attention deficit hyperactivity disorder.Now, a brain-imaging study offers more evidence that could lead to new ways to treat it.Researchers say they observed shortages in the brain’s reward system in patients with A．D.H.D..The study found that levels of some proteins were lower than normal.Nora Volkow, director of the National Institute on Drug Abuse, says the lack of attention and self-control that mark A．D.H.D. could be caused by problem in the flow of dopamine(多巴胺). She says people might have difficulty completing an activity if they cannot expect some kind of reward in return. Researchers studied the pathways on which dopamine travels and A．D.H.D. Doctor Volkow says the researchers then compared the pathways to those of 44 adults without the disorder. “There is a lower concentration of dopamine markers in the brain of individuals with A．D.H.D., specifically in the areas of the brain that are involved with reward and motivation. And the dopamine levels are directly linked to the severity of the patient’s inattention，”she says.

　　The study used brain images taken at Brookhaven National Laboratory in New York State. Jack Wang is chairman of the Brookhaven medical department. He says the finding might also help explain why people with A．D.H.D.are more likely to abuse drugs or overeat. He says they might be attempting to increase their dopamine levels to make up for the deficits in their reward system.(2011·合肥模拟)

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