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A structural-functional basis dyslexia in cortex of Chinese readers中文读者阅读障碍皮层结构功能基础

中文读者阅读障碍的皮层结构功能基础

Astructural–functionalbasisfordyslexiainthecortexofChinesereaders

WaiTingSiok ,ZhendongNiu§,ZhenJin¶,CharlesA.Perfetti ,andLiHaiTan

ofLinguisticsand StateKeyLaboratoryofBrainandCognitiveSciences,UniversityofHongKong,PokfulamRoad,HongKong;ofComputerScienceandTechnology,BeijingInstituteofTechnology,Beijing100081,China;¶Beijing306Hospital,

Beijing100101,China;and LearningResearchandDevelopmentCenter,UniversityofPittsburgh,Pittsburgh,PA15260

§College Department

CommunicatedbyRobertDesimone,MassachusettsInstituteofTechnology,Cambridge,MA,February25,2008(receivedforreviewJanuary1,2008)

Developmentaldyslexiaisaneurobiologicallybaseddisorderthataffects 5–17%ofschoolchildrenandischaracterizedbyasevereimpairmentinreadingskillacquisition.Forreadersofalphabetic(e.g.,English)languages,recentneuroimagingstudieshavedem-onstratedthatdyslexiaisassociatedwithweakreading-relatedactivityinlefttemporoparietalandoccipitotemporalregions,andthisactivitydifferencemayre ectreductionsingraymattervolumeintheseareas.Here,we nddifferentstructuralandfunctionalabnormalitiesindyslexicreadersofChinese,http://www.wenkuxiazai.comparedwithnormallydevelopingcon-trols,http://www.wenkuxiazai.comingfunctionalMRItostudylanguage-relatedactivationofcorticalregionsindyslexics,wefoundreducedactivationinthissameleftmiddlefrontalgyrusregioninChinesedyslexicsversuscontrols,andtherewasasigni cantcorrelationbetweengraymattervolumeandactivationinthelanguagetaskinthissamearea.Bycontrast,Chinesedyslexicsdidnotshowfunctionalorstructural(i.e.,volumetricgraymatter)differencesfromnormalsubjectsinthemoreposteriorbrainsystemsthathavebeenshowntobeabnormalinalphabetic-languagedyslexics.Theresultssug-gestthatthestructuralandfunctionalbasisfordyslexiavariesbetweenalphabeticandnonalphabeticlanguages.

brainfunction Chineselanguage culture readingdisorder neuroimaging

D

evelopmentaldyslexiaischaracterizedbyunexpectedlylowreadingabilityinpeoplewhohaveadequateintelligence,typicalschooling,andsufficientsocioculturalopportunities(1–10).Earlyinvestigationsofpostmortemdyslexicbrainsrevealedstructuralabnormalitiesinbothcorticalandsubcorticalareas(11,12).Recentneuroimagingstudiesexaminingstructure–functionrelationshipswithalphabeticlanguageshavefurtheridentifiedseveralbrainregionswithatypicalfunctionandanom-alousstructureindyslexia,includinglefttemporoparietalareas,whicharethoughttobeinvolvedinletter-to-soundconversionsinreading(1–8,13–18),theleftmiddle-superiortemporalcortex,whichisthoughttobeinvolvedinspeechsoundanalysis(17–22),andtheleftinferiortemporo-occipitalgyrus,whichmayfunctionasaquickwordformrecognitionsystem(18,20,22–27).Together,thesefindingssupportaprominentneurophysiologicalmodelofreadingskillacquisitionanditsdisordersaccordingtowhichdyslexiaisassociatedwithatypicalstructuralandfunc-tionaldevelopmentofposteriorbrainsystems(1–10).

Theneuralcircuitsinvolvedinreadingandreadingdisordersmayvaryacrosslanguages,becauseofdifferencesinhowawritingsystemlinksprinttospokenlanguage(4–7,28–30).Forexample,inlogographicChinese,graphicforms(characters)aremappedtosyllables,whichdiffersmarkedlyfromanalphabeticsystem(e.g.,English)inwhichgraphicunits(letters)aremappedtophonemes.Thesedifferencescanleadtodifferencesinhowreadingissupportedinthebrain.ReadersofChineseshowrelativelymoreengagementofvisuospatialareasandleftmiddle

http://www.wenkuxiazai.com cgi doi 10.1073 pnas.0801750105frontalregionsforverbalworkingmemory,presumablyforrecognizingcomplex,square-shapedcharacterswhosepronun-ciationsmustbememorizedbyroteinsteadofbeinglearnedbyusingletter-to-soundconversionrules(31–35).InanfMRIstudy,wepreviouslyshowedthat,unlikeimpairedreadinginEnglishandotherWesternlanguages,impairedreadinginlogographicChineseisassociatedwithfunctionaldisruptionofprocesseslocalizedtotheleftmiddlefrontalgyrus(28).Al-thoughChinesedyslexiaismanifestedbyaphonologicaldeficit(i.e.,graphicformtosoundconversion),whichissimilartodyslexiainalphabeticlanguages(29),corticalregionsmediatingthisdeficitinChineseandalphabeticlanguagesarespatiallyseparated.Therefore,theneuralmechanismsunderlyingim-pairedreadingmaydependonthewritingsystemused.

WithfMRIalone,however,itisdifficulttoknowwhetheractivationdifferencesfoundinabehavioraltaskareacauseoreffectofabraindisorder,suchasdyslexia.WehypothesizedthattheremaybeadifferentstructuralbasisforreadingimpairmentinChinesedyslexicsthatdiffersfromthatfoundinWesternlanguagereaders.

TodeterminebrainstructuredifferencesindexedbygraymattervolumebetweenChinesedyslexicandcontrolgroups,weusedanestablishedwhole-brainassessmenttechnique,voxel-basedmorphometry(VBM)(1)toanalyzethehigh-resolution3DanatomicalimagesacquiredwithMRIsfrom16Chinesedyslexicsubjectsand16age-matchednormalcontrols(averageage11;Table1).Inaddition,afunctionalMRI(fMRI)exper-imentwasconducted,inwhichasubsetof12ofthe16dyslexicsand12ofthe16controlsubjects(averageage11)whowereavailablefortheadditionalfMRIscanwereaskedtodecidewhethertwocharactersviewedsimultaneouslyrhymedwitheachother.Therhymejudgmenttaskinvolvesphonologicalprocess-ing,allowingustomakeaclosecomparisonbetweenthepresentfindingswiththosefromrecentneuroimagingexperimentsusingthesimilartasktostudydyslexiainEnglishreaders(1,14,23).Results

AtypicalBrainStructureinChineseDyslexia.TheVBManalysis

showedthat,whiletherewasnosignificantdifferenceintotalgraymattervolumebetweenthetwogroups[t(30) 1.52,P 0.14],regionalgraymattervolumeintheleftmiddlefrontalgyruswassignificantlysmallerindyslexicreadersthaninnormalsubjects[Brodmannarea(BA)9;x 32,y 31,z 28;Z-score 5.61;P 0.05correctedformultiplecomparisonsusingthefamily-wiseerror(FWE),correctionforthewholebrain](Fig.1a,b,andd).Nootherbrainregionssurvivedthisstatisticallevel,althoughatalessstringentuncorrectedstatis-ticalthresholdofP 0.001reducedgraymattervolumewasseen

Authorcontributions:W.T.S.,C.A.P.,andL.H.T.designedresearch;W.T.S.,Z.J.,andL.H.T.performedresearch;W.T.S.,N.Z.,andL.H.T.analyzeddata;andW.T.S.,C.A.P.,andL.H.T.wrotethepaper.

Theauthorsdeclarenocon ictofinterest.

To

whomcorrespondenceshouldbeaddressed.E-mail:tanlh@hku.hk.

©2008byTheNationalAcademyofSciencesoftheUSA

PNAS April8,2008 vol.105 no.14 5561–5566

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A structural-functional basis dyslexia in cortex of Chinese readers中文读者阅读障碍皮层结构功能基础

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