New research suggests that drug therapy that increases levels of the neurotransmitter(神経伝達物質)norepinephrine in children with Down syndrome may reverse learning deficits(障害、不足)associated with the congenital(先天的な)disorder. Although children with Down syndrome are not developmentally delayed at birth, they fall behind(後れをとる)as they age and suffer from contextual learning and memory deficits. In a study of mice genetically engineered to have a Down syndrome-like condition, researchers found that artificially boosting levels of norepinephrine had an almost instantaneous positive effect.