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Developmental Cognitive Neuroscience

jou rn a l h om epa g e:h t t p : / / w w w . e l s e v i e r . c o m / l o c a te / d c n

Enhanced efficiency of the executive attention network after training in preschool children: Immediate changes and effects after two months

M. Rosario Rueda

, Puri Checa, Lina M. Cómbita

Dept.PsicologíaExperimental,UniversidaddeGranada,Spain

a r t i c l e i n f o

Articlehistory:

Received20June2011 Receivedinrevisedform 23September2011 Accepted27September2011

Keywords:

Training

Executiveattention Conflictresolution ERPs

Fluidintelligence Affectregulation

a b s t r a c t

Executiveattentionisinvolvedintheregulationofthoughts,emotionsandresponses.This function experiencesmajordevelopmentduring preschoolyearsandisassociated toa neuralnetworkinvolvingtheanteriorcingulatecortexandprefrontalstructures.Recently, therehavebeensomeattemptstoimproveattentionandotherexecutivefunctionsthrough training.Inthecurrentstudy,agroupof5yearsoldchildren(n=37)wereassignedtoeither atraining-groupwhoperformedtensessionsofcomputerizedtrainingofattentionoranon- trainedcontrolgroup.Assessmentofperformanceinarangeoftasks,targetingattention, intelligenceandregulationofaffectwascarriedoutinthreeoccasions:(1)before,(2)after, and(3)twomonthsaftercompletionoftraining.Also,brainfunctionwasexaminedwitha high-densityelectroencephalogramsystem.Resultsdemonstratethattrainedchildrenacti- vatetheexecutiveattentionnetworkfasterandmoreefficientlythanuntrainedchildren, aneffectthatwasstillobservedtwomonthsafterwithoutfurthertraining.Also,evidence oftransferofattentiontrainingtofluidintelligenceand,toalesserdegree,toregulation ofaffectwasobserved.Resultsshowthatefficiencyofthebrainsystemunderlyingself- regulationcanbeenhancedbyexperienceduringdevelopment,providingopportunities forcurricularimprovement.

© 2011 Elsevier Ltd. All rights reserved.

1. Introduction

One of the major changes that take place over the course of human development occurs in the domain of executive control. With age, children go from external regulationoftheirbehavior,oftenprovidedbycaregivers and/or changesinstimulation, toan increasedabilityto self-regulateemotionsandactions.Mechanismsofatten- tionhavebeenimplicatedinaction-regulationfromearly theoretical models (James, 1890; Norman and Shallice, 1986).AccordingtoPosner’sneurocognitivemodel,atten- tion is related to the function of three brain networks involvedin (1) reachingand/or maintaining thealerting

∗ Correspondingauthorat:Dept.PsicologíaExperimental,Universidad deGranada,CampusdeCartujas/n,18071Granada,Spain.

Tel.:+34958249609.

E-mailaddress:[email protected](M.R.Rueda).

state,(2) orientingattentionandselecting thesource of stimulation, and (3) regulating thoughts, emotions and action.The thirdfunctioniscarriedout bythe so-called executive attention network, which involves the ante- riorcingulatecortex(ACC) and prefrontalregionsof the brain (Posner and Petersen, 1990; Posner et al., 2007).

Functionsassociatedwiththeexecutiveattentionnetwork overlaptosomeextentwiththemoregeneraldomainof executivefunctions(EFs),whichencompassasetofinter- related processes involved in planning and carryingout goal-directedactions, includingworking memory(WM), mental-set switchingor attentionalflexibility,inhibitory control,andconflictmonitoring(BlairandUrsache,2011;

Welch, 2001; Welsh and Pennington, 1988). These cog- nitive abilitiesarerequiredwhen itis necessarytohold information in mind, manage and integrateinformation and resolve conflict between sources of stimulation or responseoptions.

1878-9293/$–seefrontmatter © 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.dcn.2011.09.004

Developmentalstudieshavesuggestedthat the three attentionnetworks consideredin Posner’s modelfollow differentmaturationalcourses(PosnerandRueda,inpress;

Ruedaetal.,2004a).Thealertingandorientingnetworks appeartomaturelargelyduringinfancyandearlychild- hood,althoughbothnetworkscontinuedevelopingupto latechildhood,showingimprovementsintheendogenous controlof processes relatedto preparationand selectiv- ity.Theexecutiveattentionnetworkappearstoundergo a more progressive maturation, emerging at about the end ofthe first yearof lifeandcontinuingduringchild- hoodintoadolescence.However,despitethe progressive improvementthroughout childhood,executive attention shows a major period of development from about the end of the first year of life up to about 7 years of age (Rueda et al., 2004a, 2005a). Maturation of this func- tionislikely relatedtostructural changesinbrainareas that are part of the executive attention network and their connectivity patterns with other brain structures, in particular, the emergence of greater fronto-parietal functional connectivityover development (Power et al., 2010).

A widely used strategy to study executive attention in cognitive research is to utilize conflict tasks (Posner andDiGirolamo, 1998).These involvesuppressingeither processing or responding to information that elicits an incorrect or inappropriate response. One of these isthe flankertask(EriksenandEriksen,1974).Inthistask,atar- getstimulus is surrounded by stimulationthat suggests eitherthe same(congruent) ora different(incongruent) responsethantheoneassociatedtothetarget.Suppressing theprocessingofthedistractinginformationintheincon- gruentconditionrequiresattentionalcontrolandactivates theexecutiveattentionnetworktoagreaterextentthan whenthereisnoconflictbetweentargetandflankers(Fan etal.,2003).

Theabilitytoregulatebehaviorinaflexible andcon- trolled modehas proven to be central tomany aspects of children development. Individual differences in effi- ciencyofexecutiveattentionappeartoplayanimportant roleinschoolcompetenceandsocialization(Checaetal., 2008; Eisenberg et al., 2010, 2011; Rueda et al., 2010).

Several studies have shown that children with greater executiveattentionefficiency(i.e.smallerconflictscores) showhigherlevelsofcompetenceatschool,understand- ingcompetenceasacombinationofschoolachievement andadequatesocio-emotionaladjustmentintheclassroom (BlairandRazza,2007;BullandScerif,2001;Checaetal., 2008;Ruedaetal.,2010).Recently,wehaveshownthatthe brainreactiontoconflict,asmeasuredwithevent-related potentials, also predict children’s grades in math above andbeyondgeneralintelligence(ChecaandRueda,2011).

Moreover,higherlevelofattentionalandeffortfulcontrol helps on the prevention of developing psychopatholo- gies,suchasexternalizingbehavioralproblemsandADHD (Eisenberg et al., 2005; Rothbart and Posner, 2006). All these data show the prospect for a potentialbenefit of promoting children’s attention regulationskills through educationalinterventions.

In recent years, several studies have reported posi- tive effects of training different aspects of attention in

children. Mostof the studieshaveusedcomputer-based tasks or sets of exercises targeting particular abilities.

Kernsetal.(1999)showedimprovementinanumberof attention measures in ADHDchildren after applying an intervention programcombiningvigilance, selectiveand executiveattentionrequirements.Also,normallydevelop- ingpreschoolchildrenhavebeen showntobenefitfrom a trainingprogram targetingexecutive attention(Rueda etal.,2005b).Otherstudieshavealsoshownimprovements in attentional flexibility after task-switching training in bothchildrenandadults(KarbachandKray,2009;Minear and Shah,2008). Besides,anincreasing numberofstud- ieshaveexaminedsusceptibilityofotherEFscomponents tobe enhancedby training.Training of WMhas proven to have beneficial effects on WM abilities in normally developing children (Thorell et al., 2009), children with ADHD (Klingberg et al., 2005), and adults (Jaeggi et al., 2008).

Interestingly,mostofthestudiesdescribedabovehave also reported transfer effects of trainingto fluid intelli- gence. For instance, gains in reasoning skills have been foundaftertrainingofWM(Jaeggietal.,2008;Klingberg etal.,2005),task-switching(KarbachandKray,2009),and executiveattention(Ruedaetal.,2005a,b).Thisevidence speaksagainsttheideaoffluidintelligenceasafixedtrait (HornandCattell,1966).Instead,itsuggeststhatfluidintel- ligenceskillscanbechanged,althoughitcouldbethecase thatreasoningskillsarelesssubjecttoeducationthancrys- tallizedintelligence.Transfertointelligenceaftertraining ofexecutivefunctionsisrelativelyunsurprisinggiventhe interrelatednatureofEFsprocessesandthefactthatmany commonregionsofthefrontallobearerecruitedbycog- nitive demands involved in generalintelligence and the variousprocessesundertheumbrellaofEFs(Duncanand Owen,2000;Duncanetal.,2000).

Severalstudieshavealsoexaminedtheeffectoftrain- ing onbrain function.Information on the neural effects of attentiontraining mostly comes from research using rehabilitation programs with patients. Sustained atten- tiontrainingwithneglectpatientswasfoundtoproduce increasedactivationinthe superiorparietalcortex,right andleftfrontalareasandACC,areasknowntobeassoci- atedwithallthreeattentionnetworks(Sturmetal.,2006;

Thimm et al., 2006). Evidence isalso availableforother EFs components. For instance, using fMRI, Olesen et al.

(2004)reported increasedactivationinareasinvolvedin WMprocessing(i.e.thesuperiorandinferiorparietalcor- tices as well as in the middle frontal gyrus) after WM traininginadults.Moreover,changesinbrainmechanisms affecting dopamine neurotransmission have also being reportedafterWMtraininginnormaladults(McNabetal., 2009).

MorelimitedevidenceisavailableontheeffectthatEFs trainingproducesinchildren’s brainfunction.Inastudy carried by our group (Ruedaet al., 2005b), the effect of training attention was characterized with event-related potentials.Wefoundthat5sessionsofattentiontraining inpreschoolchildrenproducedapatternofbrainactiva- tionthatwasmoreadult-likecomparedtotheuntrained group.Brainactivationwasregisteredwhilechildrenper- formeda child-friendlyflanker task, and changesin the

brainreactiontoconflictwascharacterizedintwodimen- sions: (1) timing of the conflict effect, which showed a shorter latencyafter training,and (2)topography of the conflicteffect,whichmovedtoposteriorleadsinthefrontal midline with training, the distribution that the flanker conflict effect shows in adults and that has been asso- ciated witha source ofactivation in the ACC (vanVeen andCarter,2002).Also,usingERPswithaselectiveatten- tionparadigm,Stevensetal.(2008)reportedanincreased differentiationbetweenattendedandunattendedprocess- ing in the brain signal (i.e. greater ability to filter-out irrelevant information) of children who underwent an intensivetrainingprogramdesignedtoimprovelanguage skills.

The aim of the present study was to further exam- ine the effect of training attention on brain function in a groupof preschool-aged children.Training focused on executiveattention,althoughalsoincludedexercisestar- getingsustainedandselectiveattention.Toexaminebrain function,ahigh-densityelectroencephalogramsystemwas usedwhile childrenperformedaflankertaskbeforeand aftertraining.Moreover,inordertostudydurabilityofthe trainingeffect,ashort-rangefollow-upsessionwascarried outtwomonthsaftercompletionofthetrainingprogram.

Finally,wewereinterestedonexamining possibletrans- fereffectstountrainedabilitiesthathavebeenrelatedto individualdifferencesonexecutiveattentionefficiency.In particular, we assessedchildren’s performance on tasks involvingregulationofaffectandintelligenceinallsessions (PRE,POST1andPOST2).

Trainingwasexpectedtoresultinincreasedexecutive attention efficiency both in performance of the conflict task and the underpinningbrain activation. In terms of brainactivation,increasesinefficiencyduetomaturation appear toresultin a reductionof the latencyand dura- tion of the conflicteffect (Jonkman, 2006; Ridderinkhof andvanderMolen,1995).Also,priorimagingstudieshave shownthatbrainactivationsrelatedtoexecutivecontrol becomemorefocusedandrefinedwithmaturation(Bunge etal.,2002;Caseyetal.,1997).Thereforeweexpectedthat trainingwouldresultinshorteningthelatency,amplitude anddurationofthebrainreactiontoconflict.Besides,we predictedthatthesourceofactivationsrelatedtotheERP effectswould alsoshowmorefocused frontal activation aftertraining.

GivenpreviousevidenceonthetransferoftrainingEFs abilities to reasoning, we also expected our training to increasefluidintelligence. Finally, wehypothesized that increasingexecutiveattentionefficiencywouldgeneralize totasksrequiringregulationofresponsesinvolvingrejec- tion of immediate rewards in exchange for delayed but morefavorableconsequences.Thishypothesiswasbased onevidencecomingfrombothdevelopmentalandimag- ing studies. Developmental studies have pointed to the ideathatchildrenwhoshowbetterattentioncontrol(i.e.

smallerconflictinterferenceintheflankertask)appearto bemoreabletoregulateaffect(Simondsetal.,2007). In addition,imagingstudieshaveprovidedevidenceforarole ofthe ACC,amajornodeof theexecutiveattentionnet- work,intheregulationofaffect(Bushetal.,2000;Ochsner etal.,2002;OchsnerandGross,2007).

2. Method

2.1. Participantsandprocedure

A total of 37 children (20 males; mean age: 64.7 months; SD: 3.2) recruited at an urban Primary School in Granada (Spain)participated in the study. Caregivers of all the children gave written consent to be involved in thestudyafterbeinginformedofits generalpurpose.

AllparticipantswereCaucasian/Europeanandhadasimi- larsocialbackground.Prerequisitesforparticipationwere havingnormalorcorrected-to-normalsensorycapacities and nohistory of chronic illnessand/or psychopatholo- gies.

Allparticipants carriedouta firstassessmentsession (PRE)attheCognitiveNeuroscienceLabofthePsychology Dept.,UniversityofGranada.Duringthissessionchildren wereadministered a set of penand paper tasks includ- ingtheDelayofGratificationandChildrenGamblingtasks and the Kaufman Brief Intelligence Test (K-BIT). After conclusionofthesetasks,childrenwerefittedwiththe128- channels Geodesic Sensor Net (www.egi.com) and were askedtoperformthe childversionofthe AttentionNet- workTask (ANT)while EEG wasrecorded. Theduration of thesession was1happroximately,includingtimefor instructionsandbreaksbetweentasks.Duringthissession, parents werealsoaskedtofilloutatemperamentques- tionnaire.

After completion of the first session, children were pseudo-randomly assigned to either the experimental (to-be-trained) or the control (untrained) group. The assignmentwasmadesochildrenineachgroupwouldbe matchedbygender,averageintelligenceandflankerinter- ferenceintheANT.Atotalof19children(10males;mean age: 65.1;SD: 3.73) were assigned to the experimental group,and18(10males;meanage:64.3;SD:2.56)tothe controlgroup.Participantsinthetwogroupsdidnotdif- ferinage(F>1)orparentaleducationallevel,andtheyall attendedthesameschool.Also,therewerenotsignificant differences (allt<1;exceptt(35)=1.7;p=.09fororient- ing and t(35)=−1.12; p=.26 overall commission errors) betweenthegroupsinthescoresoftheassessmenttasks obtainedinthePREsession.

Childreninthetrainedgroupwentthroughintervention withasetofcomputerizedexercisesforatotaloften45- minsessionsthatwerecarriedoutoveraperiodof5weeks (2sessionsperweek).Thosesessionswereconductedindi- viduallyforeachparticipantinaquietroomattheschool.

Participantsassignedtothecontrolgroupunderwentthe samenumberofsessionsinsimilarconditions(individu- allywiththeexperimenterandinaquietroomatschool) butwatchedcartoonvideosinstead.

Oncetheinterventionperiodwascompleted,children in both groups were invited to the lab in two more occasions.Thefirstpost-intervention(POST1)sessionwas carriedoutwithinaperiodofoneweekaftercompletion oftheintervention.Thesecondpost-intervention(POST2) sessionwasconductedtwomonthsaftercompletionofthe POST1session.Thetaskscompletedinthesesessionsand the procedure followedwas identical tothat of the PRE session.

3. Materials 3.1. Assessmenttasks

3.1.1. Delayofgratification(DoG)

TheDoGtaskadministeredinthis studywasamodi- fiedversionofthetaskdesignedbyThompsonetal.(1997).

Childrenwereinstructedtochoosebetweengettingaprize immediatelyorwaitinguntiltheendofthetaskinorder to(a)gettwo prizesinsteadofone(DoG_self),or(b)have someoneelse(theexperimenter)getaprizetoo(DoG_other).

Threedifferenttypesofrewardwereused:stickers,5-cents ofeurocoins,andcandies.AnexampleofaDoG_selftrialis

“Youcanchoosebetweenhavingonestickerrightnowor gettingtwoofthemwhenwefinishthegame”.Anexam- pleoftheDoG_othertrialis“Youcanchoosebetweenhaving onecoinforyourightnoworhavingoneforyouandone formeattheend ofthegame”.Twopracticetrialswere usedtoexplain the task.Experimental trialsbeganonly whenitwasclearthat thechildunderstoodthe instruc- tions.Then,eachparticipantcompleted12trials,6ofeach condition(DoG_self/DoG_other),fourwitheachtypeofreward.

Theimmediate-choicewaspresentedinthefirstpartofthe statementinhalfofthetrialsandthedelay-choicewaspre- sentedfirstinthe otherhalf.Theexperimenterprovided no feedback otherthan supplyingthe rewards immedi- atelyorputtingtheminanenvelopethatthechildwould get at completion of the task, depending on the child’s choice.Percentageofdelaychoicesineachconditionwas thedependentmeasureinthistask.

3.1.2. Childrengamblingtask

The gambling task administered in this study was a simplifiedversionoftheIowaGamblingTaskbyKerrand Zelazo(2004).Childrenhadtopickonecardatatimefrom oneoftwosetsofcardsinordertowincandies.Eachcard couldhavesmilingandsad faces printedon it.Children weretoldandshownthathappyfacesonthecardsindi- catethenumberofcandieswon,whereassadfacesindicate thenumberofcandieslost.Oneofthesetsprovidedacon- stantreward ofonesmilingface andeithernosad faces oronlyone(AdvantageousSet;ADV),consistingofalow- immediate-reward/low-winrateinthelongrun.Theother set(DisadvantageousSet;DIS)providedaconstantreward oftwosmilingfacesandcouldhaveeitherzero,two,fouror sixsadfaces,consistingofahigh-immediate-reward/high- lostrateinthelongrun.Thetwosetsofcardswereplaced infrontofthechildfacingdownsothechildwouldhaveto figurethecontingenciesofeachdeckoutprogressively.In thebeginningofthetask,childrenweregivenastakeof10 candiesinordertostartplaying.Therewere4demonstra- tiontrialsin whichtheexperimentersampledtwo cards from eachdeck.Whenacard wasturnedover, onlythe happyfaceswerevisiblewhilethesadfaceswerecovered withanote.Afterthenumberofwoncandieswasrevealed tothechildandthecandiesweresupplied,thenotewas removedrevealing the numberof candies lost. Rewards weredepositedinto,andremovedfrom(accordingtothe numberofhappyand sadfacesobtainedineachtrial),a transparentcontainersituatedin frontofthe childatan equaldistance fromeachofthe twodecks.Atotalof50

trialswereadministrated.Thedependentvariablewasthe numberofpicks fromtheADVset minusthenumberof picksfromtheDISsetmadeinthelast40trials.Theloca- tionofthetwodecksandthedesignatthebackofthedecks werecounterbalancedacrossparticipants.

3.1.3. K-BIT

The Kaufman BriefIntelligence Test (K-BIT; Kaufman andKaufman,1990)wasusedtomeasuregeneralintelli- gence.Thetestprovidesameasureofcrystallized(Verbal) intelligenceandameasureoffluidreasoning(Matrices)as wellasacompositeintelligence(IQ)score.Administration ofthetesttakesapproximately15minwithchildrenaged 4–5years.

3.1.4. ChildANT

Weusedthechildrenversionof theANTtask(Rueda etal.,2004a)tomeasureattention.Ineachtrialofthistask arowoffivefishappearingeitheraboveorbelowafixa- tionpointispresented.Childrenaretoldtopresseitherthe rightortheleftkeyonapaneldependingonthedirection inwhichthefishinthemiddleispointingwhileignoring theflankerfish,whichpointineitherthesame(congru- ent)oropposite(incongruent)directionastothemiddle fish. Before the fishappear, visual signalsare presented thatinformeitherabouttheupcomingofthetarget(alert- ingcue)onlyorabouttheupcomingofthetargetaswellas itslocation(orientingcue).Completionofthetaskallows calculationofthreescoresrelatedtotheefficiencyofthe attentionnetworksbymeansofmeasuringhowresponse timesareinfluencedby alertingcues,orientingcuesand congruencyoftheflankers.Thealertingscoreisobtained by subtractingmean(or median) RToftrialswith alert- ingsignal from that of trialswith nocue. The orienting scoreisobtainedbysubtractingRTfromtrialswithorient- ingcuefromtrialsinwhichthevisualcuewaspresented atthelocationofthefixationpoint.Finally,theexecutive attentionscoreiscalculatedbysubtractingRTfromtrials withcongruentflankersfromthatoftrialswithincongru- entflankers.Thisisconsideredanindexoftheinterference experiencedby the participantwhen incongruousinfor- mationispresentedinthe displayalong withthe target.

Largerinterferencescoresindicatelessefficiencyofexec- utiveattention.

3.1.5. EEGrecordinganddataprocessing

EEG was recorded using a high-density arrayof 128 Ag/AgClelectrodesarrangedinto anet (GeodesicSensor Net, EGI Inc., Eugene, OR)while children performedthe Child ANT during the pre- and post-training evaluation sessions. All 37 participants agreed to wear the sensor net.Impedances foreach channelremainedat or below 80k during testing. During acquisition, EEG recording was vertex-referenced and the signal was digitalized at 250Hz. Atime constant valueof 0.01Hz wasused. Off- line data were filtered using a 0.3–12Hz finite impulse response(FIR)band-passfilterandsegmentedinto200ms pre-target and 1200ms post-target epochs. Segmented fileswerescannedforeyeand/ormovementartifacts.One child(belongingtothecontrolgroup)whohadlessthan 12cleansegmentspercongruencyconditionwasexcluded

fromfurther processing.Segmentswereaveragedacross congruencyconditionsandre-referencedtotheaveraged (acrosschannels)activation.

3.2. Trainingprogram

Thetraining program wasthe sameas the oneused by Rueda et al. (2005b; also described in Rueda et al., 2007).Theprogramconsistsofseveralcomputerizedexer- cises divided in 4 categories: (1) Tracking/Anticipatory;

(2) Attention Focusing/Discrimination; (3) Conflict Res- olution; and (4) Inhibitory Control Exercises. In the current study the program was extended with three more exercises,one in the categoryof AttentionFocus- ing/Discrimination,oneintheConflictResolutioncategory and another in a new category of Sustained Attention.

Therefore,thenewprogramconsistedofatotalof11exer- cisesdividedin5generalcategories.Theexerciseswere programmedtobechild-friendlyandinvolvedplayingwith ajoystickoramouse.Allexercisesrequiredcompletionofa numberoftrialsorganizedinincreasinglevelsofdifficulty.

Mostoftheexerciseshad7levelsofdifficultyandinorder togofromoneleveltothenextthechildmustcompletea minimumofcorrectlyrespondedtrialsinarow(3,inmost exercises).

Exercises in the Tracking/Anticipation category were designed toteachthe childrentotracka cartooncaton thecomputerscreenbyusingthemouse,andmonitorthe positionofothercartoonsinthescreen.IntheSideexercise thechildisaskedtotakethecattothegrasswhileavoid- inggoingintothemud.Asthechildachieveshigherlevels, themudareagetsprogressivelybiggerandthegrassarea getssmaller,increasingthedifficultytocontrolthemove- mentofthecat.IntheMazeexercise,childrenhelpthecat togetfoodbynavigatingitthroughamazetowherethe foodis.Finally,intheChaseexercisechildrenmustantic- ipatethelocationwhereaduckthatswimsacrossapond inastraightlinewillcomeacrossinordertochasingit.In asecondversionoftheexercise(ChaseInvisible),theduck becomesinvisiblewhenitgoesintothepond,asifdiving, sothatitstrajectoryremainsinvisible.

TheexercisesintheFocusing/Discriminationcategory areoftwotypes.Thefirsttypeconsistsonmatching-to- samplegames,inwhichchildrenhavetoclickontheone of two pictures that looked exactly the same as a sam- plepicture.Similaritiesbetweenthetwooptionsincreased progressively,requiringthechildtopaycloserattention.

Therearetwoversionsoftheexercise.Inthisfirstversion (Portraits),thesamplepictureremainsonthescreenwhile thechildselectsthematchingitem.Inthesecondversion (PortraitsDelay),thesamplepicturedisappearsforcingthe childtokeepinmindtheattributesofthesamplepicture.

Thesecondtypeofexercise(Shapes)consistsofthepresen- tationofanumberofoverlappingfiguresandthechildisto determinewhicharetheonespresentedbyclickingonthe appropriatebuttonsdisplayedonthesidesofthescreen.

Difficultyisaugmentedinsuccessivelevelsbyincreasing thenumberofoverlappingshapesandthecomplexityof thepatterns.

TheConflictexercisesconsistedonStroop-likegames with numbers. In the first one (Number of Numbers),

childrenarepresentedwithtwosetsofitems.Theirjobisto clickinthegroupcomposedbythelargeramountofitems.

Inthefirstslevelsoftheexercise,setsconsistofpicturesof fruitsandthenumberofitemsineachgroupdiffersbya largeamount(e.g.,twocomparedtoeight).Asthedifficulty levelsincrease,thetwosetsaremadeofdigits,andthere- foretrialscanbecongruent(whenthelargersetofdigitsis formedbydigitsofhighervalue,forexamplefournumbers 8vs.twonumbers1)orincongruent(whenthelargerset ofdigitsisformedbydigitsofsmallervalue,forexample sixnumbers2vs.fournumbers9).ThesecondStroop-like exercise(Value-Not-Size)alsoinvolvesnumbers,butinthis casetheconflictingdimensionsarevalueandsize.Insuc- cessivetrials,variousnumbers(eithertwo,threeorfour), whichdifferinsize,arepresentedandchildrenareaskedto clickonthenumberofhighervaluedisregardingthesize.

Again,there canbecongruent (thelargernumberis the onewithhighervalue)orincongruent(thelargernumber isnottheonewithhighervalue)trials.Togoonfromone difficultyleveltothenextchildrenmustcorrectlyperform threeincongruenttrialsinarow.Beforeperformingthese exercises,children completedanotherexercise in which theirknowledgeofArabicdigitswaspracticed.

Theexercise(Farmer)includedintheInhibitoryControl categoryconsistinaGo/No-Gogameinwhichthechild’s job is tohelpa farmer taking sheep insidea fence.The pictureofabaleofhayisdisplayedin themiddleofthe computerscreen.Childrenclickonthebaleofhaytofind outwhethertheanimalbehinditisasheeporawolf.Ifthe animalisasheepthechildistoclickasquickaspossibleto makeitgoinsidethefence,whereastheresponsemustbe holdtothewolf.Inadvancedlevels,thewolfdresses-upas asheepandonlyafterashortintervalitlossesitsmaskand revealsitsidentity,makingtheresponseinhibitionmore challenging.

Finally,acategoryofSustainedAttentionwasincluded.

Thisconsistsofoneexercise(Frog)inwhichchildrenare askedtohelpafrogcatch fliesthat comeoutofabottle ataparticulartimerate.Thechildmustpressakeyasfast aspossibleinordertounrollthefrog’s tongueandcatch thefly.Insometrials,theflymakesanoisebeforecoming outofthebottle.Therequirementtosustainattentionis increasedacrossblocksoftrialsbyenlargingtheintervalof timebetweenflies.

4. Results

4.1. Effectsonbehavioralmeasures

Toassesstheeffectoftrainingonthevariousbehavioral tasksincludedinthestudyweconductedasetofrepeated measuresANOVAswithSession(PRE,POST1andPOST2) and Group (Untrained vs. Trained) as factors and each ofthetasksscoresasdependentmeasure.Then,changes in thePREvs.POSTsessions (PREvs.POST1and PREvs.

POST2)scoreswereexaminedwithplannedcomparisons giventhatchangeswerepredictedafterintervention.For themeasuresthatshowedsignificantdifferencesbetween groupsatPREtest(i.e.orientingscoresand%ofcommission errorsintheANT),prescoreswereincludedascovariates intheANOVAs.ResultsontheGroup×Sessioninteraction

Table1

Meansandstandarddeviations(SD)ofallthedependentvariables(DV)includedinthestudyforeachgroupatsessionPRE,POST1,andPOST2.Thecolumns ontherightshowresultsofGroup×SessioninteractionsandplannedcontrastsperformedbetweenPREvs.POST1andPREvs.POST2scoresforeachgroup.

Task DV Group PRE POST1 POST2 Group×Session

interactionF value

Plannedcontrasts

Mean(SD) Mean(SD) Mean(SD) PREvs.

POST1

PREvs.

POST2

IQ

Matrices Trained 104 (9.6) 110 (10.45) 109 (11.6) <1 4.9^* 2.8^#

Control 107 (10.6) 112(12.47) 107(10.8) 2.5ns <1

Vocabulary Trained 110(10.8) 110(12.9) 110(10.7) <1 <1 <1

Control 107(10.2) 108.5(11.1) 106(11.6) <1 <1

Gambling V-Dlast40 trials

Trained 6.9(20.2) 12.7(18.2) 16(18.9) <1 <1 4.2^*

Control 5.11(18.5) 5.4(22.8) 3(18.2) <1 <1

DoG

Self Trained 77.2(33.9) 82.5(32.1) 84.2(29.6) 2.5^# 1.1ns 1.9ns

Control 70.6(30.5) 60.2(39.2) 68.5(41.1) 4.22^* <1

Other Trained 63.1(33.1) 61.4(42.3) 61.4(44.1) <1 <1 <1

Control 59.3(33.4) 43.5(40.1) 50.9(44.4) 4.43^* 1.15ns

ChildANT

OverallRT Trained 1071.4(241.6) 934.5(195.8) 823.8(129.6) <1 9.9^** 33^**

Control 1064.1(233) 973.2(303) 809.47(227) 4.1^* 33^**

Overall% commissionerrors

Trained 5.9(4.84) 4.6(5.8) 3.6(2.7) <1 1.2ns 2.9^#

Control 9(10.8) 6.4(10.9) 4.9(4.9) 4.2^* 8.3^**

Overall%omission errors

Trained 4.11(4.87) 3.54(6.16) 4.11(4.8) <1 <1 <1

Control 4.36(6.57) 3.9(5.74) 4.28(6.57) <1 2.05ns

Alerting Trained 12.8(148.5) 56.5(111.8) 63.3(56.03) <1 1.2 3.4^#

Control 14.3(95.6) 17.9(111.8) 59.5(54.9) <1 2.5ns

Orienting Trained 24.2(125.5) −21.6(95.7) 9.9(105.7) 2ns 1.3ns 1.1ns

Control −61.4(179) −20.0(130) 6.5(82.01) <1 1.5ns

Executive Trained 66.5(168.6) 53.5(154.1) 51.4(63.3) <1 <1 <1

Control 84.5(161.5) 72.1(183.6) 80.1(178.6) <1 <1

Significancelevel:ns:p<.10.

* p<.05.

** p<.01.

# p<.10.

andplannedcontrastforeachmeasureandgrouparesum- marizedinTable1.

4.1.1. ChildANT

Attentionnetwork scores for Alerting, Orienting and Executive Attention were obtained. Also, general per- formance indexes such as overall RT and percentage of commission and omission errors wereexamined. Alert- ingscores were calculatedby subtracting median RT to Double-Cuetrials from median RT to No-Cuetrials. The OrientingscorewascalculatedbysubtractingmedianRT in Spatial-Cue trialsfrom median RT in Central-Cue tri- als.Finally,ExecutiveAttentionscores(flankerinterference effect)werecalculatedbysubtractingmedianRTforcon- gruenttrialsfrommedianRTforincongruenttrialsforeach participantandsession(seeTable1).

ANOVAscontrastingsessionsPREandPOST1revealed a significant main effect of Session for overall RT (F(1,35)=13.34; p<.001) and for overall percentage of commission errors (F(1,35)=4.97; p<.05). Planned con- trastsshoweda reductionin overallRTforboth trained (F(1,35)=9.9; p<.001) and control (F(1,35)=4.1; p<.05) groupsatPOST1comparedtoPRE.Also,wefoundareduc- tionbetweensessionPREandPOST1inoverallcommission errorsforthecontrolgroup(F(1,35)=4.17;p<.05)which wasnotpresentforthetrainedgroup(F(1,35)=1.2;p=.27).

Noothercontrastshowedsignificantresults.

ThePREvs.POST2ANOVAsrevealedasignificantmain effect of Session for overall RT (F(1,35)=67; p<.001), overallpercentage ofcommissionerrors(F(1,35)=10.68;

p<.01),andalertingscores(F(1,35)=5.9;p<.05).Nosig- nificant Group×Session interactions were obtained for any of the scores. However, contrasts showed signifi- cantreductionsatPOST2comparedtoPREforoverallRT for both trained (F(1,35)=33.5; p<.001) and untrained (F(1,35)=33.5; p<.001) children. Also, the reduction in overallcommissionerrorsatsessionPOST2wassignificant forthe controlgroup(F(1,35)=8.3;p<.01)andmarginal for the trained group (F(1,35)=2.94; p=.09). Finally, a marginalincreaseinalertingwasobservedforthetrained group(F(1,35)=3.4;p=.07).

4.1.2. K-BIT

When including Matrices scores as DV, only the main effect of Session for PRE vs. POST1 was signif- icant (F(1,35)=7.4; p<.01). No significant effects for PRE vs. POST2 were found. Despite the non-significant Group×Sessioninteractions,plannedcontrastsshoweda significantincreaseintheMatricesscorefollowinginter- vention only for the trained group(F(1,35)=4.9;p<.05;

F(1,35)=2.6;p=.12fortheuntrainedgroup).Theincrease inMatriceswasmarginalforthetrainedgroupwhencom- paringPREtoPOST2scores(F(1,35)=2.8;p=.10)butdid not approach significance (F<1) for the control group.

Fig.1.PlotsofgrandaveragedERPswaveformstocongruentandincongruenttrialsforallchildrenatsessionPRE,andchildrenassignedtothetrained andnon-trainedgroupsatsessionsPOST1andPOST2.ThetoprowshowsERPsatchannelslocatedinanteriorfrontal(AF)positionsandthebottomrow showsEPRsatchannelsinfronto-posterior(Fcz/Cz)leads.Shadowedareasbetweenconditionsshowareasofsignificantamplitudedifferencesbetween congruencyconditions(darkgrey:p<.01;lightgrey:p<.05).Arrowheadspointtopost-targettimes(inms)forwhichtopographicmapsoft-testsdifferences werecreated(showninFigs.2and3).

For the Vocabularysubscale, no significant effects were obtainedintheANOVAsorwithplannedcomparisons.

4.1.3. Gamblingtask

NoneofthemaineffectsortheGroup×Sessioninter- actionwasfoundsignificantwhenincludingthePREand POST1dataintheANOVA.However,theGroup×Session interaction was marginally significant (F(1,35)=3.07;

p=.08) in the ANOVA including PRE vs. POST2 scores.

Planned contrasts showed that children in the training groupselectedmoreadvantageouschoicesthanthosein the controlgroup(F(1,35)=4.5;p<.05), andthat trained children increased the percentage of total choices from theadvantageous deckbetweensessionsPREandPOST2 (F(1,35)=4.17;p<.05).

4.1.4. Delayofgratification

ANOVAswereconductedseparatelyforthescores(per- centageofdelaychoices)obtainedattheDoG_self andthe DoG_otherversionsofthetask.FortheDoG_self,maineffects of Session or Group were not observed in any of the ANOVAs(PREvs.POST1orPREvs.POST2).FortheANOVA with PRE vs.POST1 scores, the Group×Session interac- tion was significant in the DoG_self task (F(1,35)=4.91;

p<.05).Plannedcontractsshowedthatuntrainedchildren decreasedthepercentageofdelaychoicesbetweenPREand POST1sessions(F(1,35)=4.22;p<.05)andthatthetrained group had the tendencyto delaymore thanthe control group following intervention (F(1,35)=3.58;p=.07). For theDoG_otherversionofthetask,thepatternofresultswas similar.Theonlysignificantdifferenceobservedoccurred betweenpercentageofdelaychoicesfromsessionPREto POST1 for children in the control group (F(1,35)=4.43;

p<.05).

4.2. Effectsonbrainelectrophysiology

4.2.1. ERPs

Target-lockedERPspercongruencyconditionarepre- sentedinFig.1fortheentiresampleatsessionPREandfor childrenatthetrainedandnon-trainedgroupsatsessions POST1andPOST2.ERPspertainingtothePREintervention session showed amplitude differences between con- gruency conditions (i.e. larger negative amplitudes for incongruenttrials)inleadssituatedinthefrontalmidline, as previously reported in the literature with the same (Ruedaetal.,2004b)orsimilartasks(Jonkman,2006;van VeenandCarter,2002).Toasesspossibledifferecesinthis effect between groups at the PRE-intervention session, amplitude and latency effects of congruency at frontal midline channelsin the timewindowranging from 300 to700msweretestedwithANOVAsincludingGroup(to betrainedandcontrol),Channel(AF,Fz,FczandCz)and Condition(Congruentvs.Incongruent)forbothamplitude (usingbothminimumamplitudewithinthetimewindow andadaptivemean¹values)andlatencymeasures.Inany of theseanalyses the main effectof Group or anyof its interactions with other factors approached significance (F<1in all cases exceptforthe Channel×Cond×Group interactionforlatencywhichreachedannon-significant, p=.24,Fvalueof 1.41).Giventhe absenceofdifferences between groups the waveforms are presented for the entire sample at session PRE. The top row shows ERPs at prefrontal sites (AF/Fz) andthe row at the bottomat fronto-parietal (Fcz/Cz) positions. Dependent-samples t

1 Theadaptivemeanconsistsofthemeanamplitudeofanewtimewin- dowcreatedincluding10samples(40ms)aroundthepeakofminimum amplitudefoundwithinthelargertimewindowof300–700ms.

Fig.2. Topographicmapsofsignificantamplitudedifferencesbetweencongruencyconditions(a)andcorrespondingsourcesolutions(b)foreachgroup atsessionPOST1.Arrowheadsshowtheparticulartimepoints(inms)betweenthepresentationofthetargetandtheaveragedtimeoftheresponseto whicheachtopomapcorresponds.DarkblueareasinthetopographicmapsindicatesitesinwhichamplitudeoftheERPswassignificantlymorenegative forincongruent,comparedtocongruent,trials.Thetoppartofthetopomapscorrespondstothefrontofthehead.

tests ofthe differencesin amplitudebetween congruent and incongruent conditions were carried out (usingthe t-testtoolincorporatedinthe NetStation software,EGI, Eugene,OR)foreachsamplealongtheentireERPsegment.

Areas of significant differences among conditions are shadowed in the waveforms presented in Fig. 1. Only differences in amplitude that were found significant in

atleast 10consecutivesamples(40ms)weremarkedas significantinthewaveforms.Also,topographicmapsofthe scalpdistributionofsignificantincongruentvs.congruent differences at particular post-targettimes are shown in Fig.2(session POST1) and 3(session POST2).At session POST1,trainedchildrenshowtheexpectedN2effect(i.e.

larger negative amplitude for incongruent compared to

Fig.3. Topographicmapsofsignificantamplitudedifferencesbetweencongruencyconditions(a)andcorrespondingsourcesolutions(b)foreachgroup atsessionPOST2.Arrowheadsshowtheparticulartimepoints(inms)betweenthepresentationofthetargetandtheaveragedtimeoftheresponseto whicheachtopomapcorresponds.DarkblueareasinthetopographicmapsindicatesitesinwhichamplitudeoftheERPswassignificantlymorenegative forincongruent,comparedtocongruent,trials.Thetoppartofthetopomapscorrespondstothefrontofthehead.

congruent trials)from around400msafter presentation ofthetarget,whereasuntrainedchildrenshowtheeffect around580mspost-target.Also,theeffectisobservedin more posterior sites (around Fcz) for trained compared tonon-trainedchildren,whoshowtheeffectinthesame sites(aroundFz)aswasobservedinthePREintervention session. This difference between trained and untrained childreninthetimingoftheconflicteffectisstillpresent indataobtainedatsessionPOST2,wheretrainedchildren showthe expectedN2effectaround360mspost-target, andchildreninthecontrolgroupshowtheeffectatabout 500msafterpresentationofthetarget.Wealsofoundan early negative deflection around 170ms after stimulus presentationthatwassignificantlymorenegativeforthe incongruentconditionatfrontalsitesinPOST1onlyinthe trainedgroup.ThisearlyeffectwasalsoevidentatPOST2 althoughitstopographymovedtomoreposteriorchannels (seewaveformsinFig.1andtopomapsinFigs.2and3).

Thetopographicdistributionofsignificantdifferences between flanker conditions changes differentially for trained and non-trained group in sessions POST1 and POST2.AsshowninFig.2,thelargernegativityassociated withtheincongruentconditionmovesfromanteriorsites in session PRE toa more posterior and right lateralized localizationin sessionsPOST1andPOST2forthe trained group.However,thispatternofactivationisnotobserved for children in the non-trained group who showed the conflicteffectlaterintimeandwithamoreanteriorand left lateralized distribution in POST1, similarto the one observedinsessionPRE,andamoredistributedeffectin sessionPOST2(seeFigs.2and3).

4.2.2. Sourcelocalizationanalyses

Grandaveraged (across subjects) ERPs data for each groupwereusedtocomputethemostlikelycorticalgen- eratorsofthepatternofelectricalfieldsregisteredonthe scalpwithasourcelocalizationsoftware(GeoSource,EGI, Eugene, OR). AFiniteDifference Model(FDM) wasused forinversemodeling,²inwhichtheMinimumNormLeast Squares(MNLS)algorithmisusedwithasetof2447dipoles triples(comprisingdipolesinthex,y,andzorientations) samplingthecerebralcortex.TheSun-Stok4-ShellSphere wasusedasaforwardheadmodel.Weightingwasplaced equallyacrosslocationswithregularizationcarriedoutvia TSVD(1×10⁻⁴)usingLAURA(LocalAuto-RegressiveAver- age;GravedePeraltaMenendezetal.,2004)asaconstraint.

TheRadiusofinfluencewassetto12.2mmwithanexpo- nentequalto3.

Data corresponding to the entire sample at session PRE,andsubsequentlywithtrainedanduntrainedgroups

2 TheFiniteDifferenceModel(FDM)thatisusedbyGeoSourceisbased ontheMontrealNeurologicalInstitute(MNI)databaseforestimatingits geometricalconstraints.TheMNIbrainmodelisbasedonadults.Byusing GeoSourcetoisolateneuralsourcesinpreschoolchildrenwerecognize thatthesourcemodelsmaybesubjecttosomeerrorasbrainsizeandlevel ofmaturationforcorticalstructuresinchildrenwilldifferfromthoseof adults.Nevertheless,inourstudythesourcemodelingerrorderivedfrom usinganadultbrainmodelremainsconstantforboththewithingroup comparisonaswellasacrossgroups,giventhefactthatchildreninthe twogroupswerematchedinageandgender.

at sessions POST1 and 2, were source analyzed at the post-targettimesinwhichsignificantdifferencesbetween congruencyconditionswerefound.WiththePREsession data, themainsourceswereobtainedatbilateralmedial frontal gyrus(rand lMFG;BA10),medialinferiorfrontal gyrus(mIFG;BA11),bilateralmedialtemporalgyrus(lMTG andrMTG;BA21),andaweaksourceatdorsalACC(BA32).

AROImontagewasthencreatedwiththeseareaswitha radiusof7mmaroundthedipoleofmaximumactivation, inordertotracechangesintheintensityassignedtothese dipolesinfunctionoftrainingatthePOSTsessions.Sources obtained attheseROIs(and additionalareas)fortrained and untrained groups are presented in Fig. 2 (session POST1)andFig.3(sessionPOST2).

5. Discussion

Inthisstudy,weextendedthetrainingprogramapplied by Ruedaet al. (2005b)with several newexercises,and increased from 5 to10 the numberof sessions used to train attention with a group of preschoolers. The study aimedtoreplicateandextendpriorresultsontheeffectof trainingattentionontheefficiencyoftheexecutiveatten- tionnetworkandrelatedabilities.Thespecificgoalwasto investigatewhetherapplyingthe extendedtrainingpro- gramhasaneffectontheefficiencyofexecutiveattention and the underlying brainmechanismsand to test dura- bilityoftheeffectinashort-termfollow-uptwomonths aftercompletionofthetraining.Wealsoaimedatexamin- ingwhethertrainingattentionproducestransfereffectsto untrainedabilities,althoughrelatedtoattention,suchas intelligenceandregulationofaffect.

5.1. Effectsoftrainingontheperformanceofthechild ANT

Asrevealedbytheanalyses,traininghadnosignificant effectonthebehavioralperformanceoftheANT.Overall RT andpercentage oferrorsdata clearlyshowthat chil- drenin bothgroupsbecomemoreproficientperforming the taskin postsessions.Also,attentionnetworkscores, particularly the executive attention and alerting scores, showsomeevidenceofincreasedefficiency.However,the factthatthepatternofchangeisverysimilarfortrainedand untrainedgroupsindicatesthatrepetitionofthetaskitself is responsible for the improvement. Mean interference scoresshowedsomeevidenceofareductionoftheconflict effect,indicatinggainsinefficiencyofexecutiveattention skills,forboththetrainedanduntrainedgroupsatsession POST1.However,noneoftheobservedreductionsincon- flictinterferencereachedstatisticalsignificance.Asimilar pattern wasobservedforthe Alertingscore. Thetrained groupexhibitsanincreaseinalertingaftertraining,which ismarginallysignificantwhencomparingthePREvs.POST2 scores.Meanscoresoftheuntrainedgroupalsoshowan increaseatsessionPOST2,indicatingthatthemererepeti- tionofthetaskisatleastpartiallyresponsiblefortheeffect.

Theincreaseinalertingscoreswouldindicatethatchildren becomemoreabletopreparefromthepresenceofwarning cues,makingfasterresponseswhenthishappens.Never- theless,despiteshowingchangesinthenetworkscoresin

theexpecteddirection,thosechangesdidnotreachstatisti- calsignificance.Thisislikelyduetothehighvariabilitythat childrenoftheageincludedinthestudyshowinreaction timewhenperformingthistask(largeSDs,seeTable1).It isalsoprobablethatchildrenreachaceilinglevelofper- formancewhencarryingoutthetaskinrepeatedoccasions becausethenetworkscoresobtainedbythe participants (particularlythoseinthetrained group)inpost-sessions aresimilarto the ones shownby adults(Conflict score:

61ms;Alertingscore:30ms)whenperformingthesame task(Ruedaetal.,2004a).

5.2. Transferoftrainingtofluidintelligence

Transfer of training to fluid intelligence was highly expected given prior results described in the literature.

Bothtrainedanduntrainedchildrenshowedandincrease inthematricessubscalescoreatsessionPOST1asindicated bythesignificantmaineffectofSession.However,planned contrasts showed that only observed gains for trained childrenreachedthe significancelevel. Thisresultrepli- catespreviousfindingsthattrainingofexecutiveattention improves non-trained reasoning abilities. The effect of trainingisspecificforfluidintelligenceanddoesnothave animpactintheverbalscalerelatedtolearning-dependent orcrystallizedintelligence.Interestingly,wefoundsome evidence (as indicated by a marginally significant PRE vs.POST2contrast)suggestingthatthe generalizationof trainingtofluidintelligenceisstillobservedtwomonths laterwithoutfurthertraining,whereasthematricesscore returned tothe initiallevel (F<1 for the PREvs. POST2 contrast)fortheuntrainedgroup.Transfertofluidintel- ligenceskillswasexpectedbecauseithasbeenshownthat thereisanextendedoverlapbetweenthebrainstructures implicatedingeneralintelligenceandthoseof theexec- utive attentionnetwork (Duncan et al., 2000). Our data addon toevidenceprovidedby otherstudiesindicating thatfluidintelligencecanbeimprovedwithintervention (Jaeggietal.,2008;Nutleyetal.,2011;Ruedaetal.,2005b).

Themodesteffectobservedinourstudycouldbedueto thefactthatmoreextendedinterventionsarerequiredto changecognitiveabilitiessuchasreasoningthatappearto beheritabletoanimportantextent(Cattell,1987;Grayand Thompson,2004).However,dataofthissortchallengethe ideathatfluidintelligenceisnotsubjecttotheinfluenceof educationandsocialization.

5.3. Transferoftrainingtoregulationofaffect

Anotherquestionthatwasaddressedinthisstudywas whether training of attentionwould generalizeto tasks thatarethoughttorelyonattentioncontrolskills.Inour study, we included two tasks, Children’s Gambling and DelayofGratification(DoG),toexaminetransferoftrain- ing to regulation of affect and motivation (also known as“hot”executivefunction;Hongwanishkuletal.,2005).

Regulationofmotivationaltendenciescanbeobservedin situations in which inhibition of immediate rewards is requiredinthefaceofahigherpriceinthelongterm.We foundthat children trained withour program increased thenumberofadvantageouschoicesintheGamblingTask

whencomparingperformanceatsessionsPREvs.POST2, whereasuntrainedchildrenperformedsimilarlyinallthree sessions(PRE,POST1andPOST2).Inthistask,itisnecessary toreappraisethemotivationalsignificanceofimmediate rewardsin ordertolearntochoose advantageously.Our resultsindicatethattrainedchildrenbecamemoreableto controltheirchoicesaccordingtothewins/loosescontin- genciesofeachdeck,beingmoreabletoinhibitchoosing fromthedominanthigh-rewarddeckbutsubjecttohigher potentiallooses.

FortheDoGtaskthepatternwassomewhatdifferent.In thetwoversionsofthetaskusedinourstudy(DoG_selfand DoG_other),untrainedchildrenshowedasignificantdecrease inthenumberofdelaychoicesthesecondtimetheyplayed thetask(sessionPOST1comparedtoPRE).Trainedchildren, however,didnotshowadecreaseinthepercentageofdelay choices. Aplausibleexplanationforthe dropinthe per- centageofdelaychoicesshownbychildreninthecontrol groupatthePOST1sessionisthatthesecondtimechildren performthetasktheyknowhowlongthedelayperiodis, becausetheyexperienceditatthePREsession,whichmay discouragethemfromchoosingthedelayoption.Thiscir- cumstanceisalsotrueforthetrainedgroup.However,in thiscase,trainingmayhavehelpedchildrentobemoreable tocontroldominant,yetunfavorable,responses,therefore preventingthemfromshowingadeclineinthepercentage ofdelaychoicesinpost-interventionsessions.

5.4. Effectsoftrainingonbrainfunction

Amajorgoalofourstudywastoadvanceunderstand- ingoftheneuralmechanismsoftrainingandtoexamine whether theeffect ofthe interventionon brainfunction shows signs of stability over time in a relatively short follow-uptwomonthslater.Brainelectrical activitywas recordedwithahigh-densityelectroencephalographysys- temwhilechildrenperformedachild-friendlyflankertask.

Asexpected,thecongruencyofflankersmodulatedaneg- ativecomponentoftheERPsthatwasfrontallydistributed (oftenreferredtoastheN2).Thiscomponentshowedlarger amplitudeintrialsinvolvingconflict(i.e.withincongruent flankers). Priorstudieshad reported thatpreschool chil- drenshowmodulationofthefrontalnegativitysometime later than adultsand at more anterior channels(Rueda etal.,2004b).Inthecurrentstudy,weobservedmodulation ofthefrontalnegativitystartingaround500mspost-target atsessionPRE(seeFig.1).Additionally,ourresultsrepli- catepreviousfindingsthattrainingaffectbothtimingand topographicdistributionofERPsrelatedtoconflictmoni- toring(Ruedaetal.,2005b).Theeffectofflankersonthe amplitude of the ERPs at frontal leads is shown earlier andinmoreposteriorchannelsfortrainedchildrencom- paredtochildreninthecontrolgroup(Fig.1).Moreover, the pattern appearstobe maintainedtwo monthslater, astrainedchildrenshowtheexpectedlargernegativityfor incongruenttrialsearlier(from360mspost-targeton)than non-trainedchildren(seealsotopomapsofsignificantcon- gruencyeffectsinFigs.2and3).Inadults,theconflictN2 effecthasbeenassociatedwithasourceofactivationinthe ACC(vanVeenandCarter,2002).Thereisevidencesuggest- ingthattheACCisinvolvedindetectingtheoccurrenceof

conflict,whichisthenconveyedtoprefrontal structures inchargeofresolvingtheconflict(Botvinicketal.,2004;

Walshetal.,2011).Thus,adelayedfrontalnegativitymay beindicativeofpoorerefficiency oftheexecutive atten- tionnetwork relatedto aslower detectionof conflictin childrencomparedtoadults.Datafromourstudysuggest thatoneoftheprocessesbywhichtrainingmayinfluence theexecutiveattentionnetworkisbyhasteningtheneu- ralmechanismssupportingthedetectionandsignalingof conflictfromtheACCtoprefrontalstructures.

Data from source localization analyses are also con- sistent with the idea of a more efficient activation of theexecutiveattentionnetworkintrainedchildren.Mod- eledimagesofelectrophysiologydataidentifiedthemore likely neural generators of the effects observed in the ERPs.Figs.2and 3showthe sources ofactivation mod- eledfromthetopographicmapsoftheincongruentminus congruent difference in electrical recordings at times in whichsignificantdifferencesinamplitudebetweenthose two conditions wereobserved. Overall, generatorswere localizedatmedialinferiorfrontal(BA11),medial–lateral PFC(mlPFC),medialfrontalgyrus(BA10),anddorsalACC (BA24/32).Thepatternofactivationisconsistentwiththe oneobservedwithsimilartasksinsomewhatolderchildren usingfMRI(Bungeetal.,2002;Konradetal.,2005).Besides, source modeling data demonstrate that children in the trainedgroupshowearlierengagementofdorsalACCthan theuntrainedcontrols,whoonlyshowaclearACCgenera- torthethirdtimetheyperformthetask(sessionPOST2).In addition,sourcesofactivationinmlPFCbecomemorelater- alizedtotherighthemisphereaschildrengainexperience withthetask(POST2comparedtoPOST1).However,this lateralizationtotherightisonlyobservedforthetrained group. Imagingstudiesof interference suppression have reported activation in ventro-lateral PFCthat is leftlat- eralizedinchildrenbutrightlateralizedinadults(Bunge etal.,2002;Konradetal.,2005).Moreover,therightvlPFC activationinadultscorrelatespositivelywiththeabilityto suppressinterference(Bungeetal.,2002).Thesedatasug- gestthatchildreninthetrainedgroupmaybeshowinga moreadult-likepatternofbrainactivationwhileperform- ingthetaskthanchildreninthecontrolgroup.However, comparisonofsourcemodeledERPsdatainchildrenand fMRIdata obtained withadultsmustbe donewith cau- tion(seeNote2)andthisinterpretationshouldbesubject toreplicationusingmorecomparablebrainimagingtech- niques.

Afinalremarkableresultofthesourcelocalizationdata isrelatedtothestrengthofactivationandfocalizationof themodeledsources.Overall,childreninthenon-trained group show broader and stronger activations than chil- dreninthetrainedgroup.Theideathatcorticalfunction becomes less diffuseand more focal withmaturation is welldocumentedinrecentneuroscienceresearch(Casey etal.,2005; DurstonandCasey,2006).Moreover,tuning ofactivations appearstobe dependentof thefunctional significance of the circuitry of brain structures,display- ingattenuatedactivationsinareasrelativelylessinvolved inaparticularfunctionandmorefocalactivationofareas relatedto thatfunction(Durstonet al.,2006; Fairet al., 2007). Our source modeling results show more focused

activation fortrained childrenin nodes ofthe executive attentionnetwork,whichsuggeststhat activationofthis networkbecomesmorefine-tunedaftertraining.

5.5. Limitationsofthestudy

Inourstudy,avideo-watchingnon-activecontrolgroup was used to examine the effect of training. The video- watching control may not be optimal for disentangling effectsthatarespecifictotheattentiontrainingaspectsof thecomputerizedprogram.However,thevideo-watching situationsharesseveralaspectswiththetrainingexperi- ence,inthatitinvolvesinteractingwithacomputerscreen inthepresenceoftheexperimenterforaperiodoftime.

Also,priorstudiesreportednodifferencesbetweenactive andpassivecontrolgroupsintrainingstudiesconducted withpreschoolers(Thorelletal.,2009;Ruedaetal.,2005b).

Infuturestudies,itmaybemoreappropriatetoincludean activecontrolgroup.Theactivecontrolcouldeithercarry out atraining programdesigned to improvea cognitive abilitythatisnon-specificforattentionorjustperformthe mostbasiclevelsoftheexercisesincludedinthetraining program.

To our knowledge, our study is the first to examine durabilityoftrainingeffectsoncognitiveandbrainfunc- tion inchildren.However,the amountoftrainingin the current studywasonly moderatebothintermsof num- ber of sessions (a totalof 10) and time (a maximumof 500min in total over a period of 5 weeks). In spite of this,wefound someevidenceoflasting effectsof train- ingtwomonthslateronsomeofthemeasuresusedinthe study,whichweremoreclearlyobservedinbrainfunction.

We believe that producinga larger impact oncognition wouldrequiremoreextendedinterventions.Asamatter offact,thereisevidenceshowingthatcurricularinterven- tionsbasedonVygotsky’stheoryofdevelopmentinvolving teacher–studentsexchangesorinteractionsbetweenpeers resultinincreasedperformanceofconflicttasksandhence betterexecutiveattentionefficiency(Diamondetal.,2007).

Similarly,experiencesthatarelikelytobemoreextended intime,suchasbeingexposedtomorethanonelanguage duringdevelopment,appeartohaveapositiveimpactin attentioncontrolskillsasmeasuredbytheANT(Yangetal., 2011).

Inourstudy,wedidnotfindacleareffectoftrainingon performanceoftheANT.Onequestionthatemergesfrom thepatternofbehavioralresultsinourstudyiswhy,despite notobtainingsignificanttrainingeffectsonthetasktarget- ingtheclosestcognitiveskills(thechildANT),significant effectswereobservedforintelligenceandmoderatelyfor emotionregulation.Standarddeviationsofscoresforeach taskpresentedinTable1suggestthatdifferencesinper- formancevariabilitybetweentheANTtaskandtherestof behavioralmeasuresincludedin thestudycouldexplain the factthattheeffectofinterventionisobservedinthe paperand penciltasksand notin theANT.Additionally, improvementsobservedforthecontrolgroupintheANT taskatpostsessionssuggestthatpracticingmaybeanother formofusefultraining.Also,thefactthatscoresobtainedat postinterventionsessionsforbothtrainedanduntrained childrenreachedadultslevelsofperformancesuggeststhe