Arecentstudyshowsthatdirtmaybegoodforbrainandmakechildrensmarterbecauseitisa

　　naturalanti-anxietydrugwithoutside-effects.Dr.DorothyMatthews,anassociateprofessorofbiologyatTheSageCollegesinTroy,N.Y.,conductedtheexperiment.Sheandhercolleaguestestedhowlongthemicetooktonavigateamaze.Theresultisthatthebacteria-exposedmicerantwiceasfastasthecontrols.Theirexplanationislikethis:Serotoninplaysabigroleinmodulatingmood,decreasinganxiety.Ifoneisnervousorfrightened,hecan’tthinkstraight.Soserotoninisofsignificanceforlearning.Intheexperiment,thebacteria-exposedmiceshowedfeweranxietybehaviorsthanthenon-exposedones.Inanotherexperiment,theresearchersremovedthebacteriafromthefoodprovidedfortheexposedmiceandfoundthatthoseexposedmicewerestillfasterthanthecontrols.Therefore,theycametoaconclusionthattheeffectistemporary.(字数：155,实际已经说清楚了.)