Congested cities are fast becoming test tubes for scientists studying the impact of traffic fumes on the brain. As roadways choke on traffic, researchers suspect that the tailpipe exhausted【M1】______ from cars and trucks—especially tiny carbon particles already implicated heart disease, cancer and respiratory ailments—may【M2】______ also injure brain cells the key to learning and memory. New【M3】______ public-health studies and laboratory experiments suggest that, at every stage of life, traffic fumes exact a measuring toll on mental【M4】______ capacity, intelligence and emotional stability. Children in areas affected by high levels of emissions, on average, scored more poor on intelligence tests and were more【M5】______ prone to depression, anxiety and attention problems than children growing in cleaner air, separate research teams in New York,【M6】______ Boston, Beijing, and Krakow, Poland, found. And older men and women long exposing to higher levels of traffic-related particles【M7】______ and ozone had memory and reasoning problems effectively added【M8】______ five years to her mental age, other university researchers in Boston【M9】______ reported this year. The emissions may also height the risk of【M10】______ Alzheimers disease and speed the effects of Parkinsons disease. 'The evidence is growing that air pollution can affect the brain,' says medical epidemiologist Heather Volk at USCs Keck School of Medicine. 'We may be starting to realize the effects are broader than we realized.' 【M1】