Probing the relevance of the hippocampus for conflict-induced memory improvement

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ContentslistsavailableatScienceDirect

NeuroImage

journalhomepage:www.elsevier.com/locate/neuroimage

Probing the relevance of the hippocampus for conﬂict-induced memory improvement

Markus Ramm

^a^,^b

, Benedikt Sundermann

^c^,^d^,ⁱ

, Carlos Alexandre Gomes

^a

, Gabriel Möddel

^e

, Lisa Langenbruch

^e

, Mahboobeh Dehghan Nayyeri

^c^,^h

, Peter Young

^f

, Bettina Pﬂeiderer

^c

, Ruth M. Krebs

^g^,¹

, Nikolai Axmacher

^a^,¹^,^∗

aDepartment of Neuropsychology, Institute of Cognitive Neuroscience, Faculty of Psychology, Ruhr University Bochum, Universitätsstr. 150, 44801 Bochum, Germany

bNeurobiology and Genetics of Behavior, Department of Psychology and Psychotherapy, Centre for Biomedical Education and Research (ZBAF), Witten/Herdecke University, Witten, Germany

cInstitute of Clinical Radiology, Medical Faculty – University of Muenster – and University Hospital Muenster, Muenster, Germany

dInstitute of Radiology and Neuroradiology, University of Oldenburg, Evangelisches Krankenhaus, Medical Campus, Oldenburg, Germany

eDepartment of Neurology with Institute of Translational Neurology, University Hospital Muenster, Muenster, Germany

fDepartment of Neurology, Medical Park Bad Feilnbach Reithofpark, Bad Feilnbach, Germany

gDepartment of Experimental Psychology, Ghent University, Ghent, Belgium

hDepartment of Psychosomatic Medicine and Psychotherapy, LVR Clinic, Medical Faculty of the Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany

iResearch Center Neurosensory Science, University of Oldenburg, Oldenburg, Germany

a r t i c le i n f o

Keywords:

Hippocampus Memory

Mesial temporal lobe epilepsy Response conﬂict

a b s t r a ct

Thehippocampusplaysakeyroleforepisodicmemory.Inaddition,asmallbutgrowingnumberofstudieshas shownthatitalsocontributestotheresolutionofresponseconﬂicts.Itislessclearhowthesetwofunctionsare related,andhowtheyareaﬀectedbyhippocampallesionsinpatientswithmesialtemporallobeepilepsy(MTLE).

Previousstudiessuggestedthatconflictstimulimightbebetterremembered,butwhetherthehippocampusis criticalforsupportingthisinteractionbetweenconflictprocessingandmemoryformationisunknown.Here,we tested19patientswithMTLEduetohippocampalsclerosisand19matchedhealthycontrols.Participantsper- formedaface-wordStrooptaskduringfunctionalmagneticresonanceimaging(fMRI)followedbyarecognition taskforthefaces.Wetestedwhethermemoryperformanceandactivityinbrainregionsimplicatedinlong-term memoryweremodulatedbyconflictduringencoding,andwhetherthisdifferedbetweenMTLEpatientsandcon- trols.Incontrols,welargelyreplicatedpreviousfindingsofimprovedmemoryforconflictstimuli.WhileMTLE patientsshowedresponsetimeslowingduringconflicttrialsaswell,theydidnotexhibitamemorybenefit.In controls,neuralactivityofconflictresolutionandmemoryencodinginteractedwithinahippocampalregionof interest.Here,lefthippocampalrecruitmentwaslessefficientformemoryperformanceinincongruenttrialsthan incongruenttrials,suggestinganintrahippocampalcompetitionforlimitedresources.Theyalsoshowedanin- volvementofprecuneusandposteriorcingulatecortexduringconflictresolution.Botheffectswerenotobserved inMTLEpatients,whereactivationoftheprecuneusandposteriorcingulatecortexinsteadpredictedlatermem- ory.Furtherresearchisneededtofindoutwhetherourfindingsreflectwidespreadfunctionalreorganizationof theepisodicmemorynetworkduetohippocampaldysfunction.

1. Introduction

Onlyasmallproportionofourexperiencesistransferredintolong- termmemory.Howlong-termmemoryencodinginteractswithcogni- tivecontrolandwhichbrainareassupporttheirrelationshiphasbeen studied, butmany questions remain (Chun andTurk-Browne, 2007; RichterandYeung,2012).

∗Correspondingauthor.

E-mailaddress:[email protected](N.Axmacher).

1 Theseauthorscontributedequally.

Inexplicitlearningtasks,attentionimprovesmemoryencoding.Con- versely,explicitmemoryperformancedeteriorateswhensubjectsper- formademandingsecondarytask(ChiuandEgner,2015;Craiketal., 1996).Thissuggeststhatcognitivecontrolandmemoryencodingrecruit similarresource-limitedneurocognitiveprocessesinfrontalandparietal regions(Reynoldsetal.,2004).Bycontrast,inimplicitlearningtasks, evenhighlydemandingtaskswhichrelyonbrainstructuresthatsup- portmemoryfunctionsmayimprovememoryencoding(Blumenfeldand Ranganath, 2006). For example, a task-switching paradigm caused impaired memory for task-relevant but improved memory for task- irrelevant information(RichterandYeung,2012).Thissuggeststhat

https://doi.org/10.1016/j.neuroimage.2020.117563

Received8June2020;Receivedinrevisedform3November2020;Accepted5November2020 Availableonline13November2020

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memoryperformancedependsontheselectivityofattention,i.e.inthe contextoftask-switching,theabilitytomaintainastabletasksetandto eﬀectivelyshieldtherelevantstimulifromdistraction.

Aninfluentialtheory ofconflictmonitoringandcognitivecontrol postulatesthatconflictininformationprocessingsignalsreinforcement oftop-downcontrolofattentiontothecurrenttask,whichhelpsresolv- ingconflict(Botvinicketal.,2001).Thistheoryfurtherassumesthat whiletheanteriorcingulatecortexprovidestheconflictsignal,thedor- solateralprefrontalcortex(dlPFC)underliescognitivecontrolmecha- nismsthatenhanceattentiontotask-relevantstimuli(Botvinicketal., 2004).Asaresult,stimulithatarepresentedwithincongruentdistrac- torsshouldtriggerenhancedselectiveattentionandimprovememory encodingoftherelevantstimulus.Wetestedthishypothesisinaprevi- ousstudythatcombinedaface-wordStroopparadigmwithadelayedin- cidentalmemorytask(Krebsetal.,2015).Trial-uniquemaleandfemale faceswereoverlaidwithcongruentorincongruentdistractorwords(the words“man” or“woman”).Thisstudyshowedthatprocessingincongru- enttrialselicitedbehavioralcosts(i.e.,longerreactiontimes),butalso improvedlatermemoryperformancefortherelevantstimulus.Conflicts inducedactivationofacommoncognitivecontrolnetwork,including dlPFCandprecuneus, andrecruitmentof these areaswas associated withamemorybenefitforfacestimuliinconflicttrials.Furthermore, functionalcouplingbetweentheseareasandthemedialtemporallobe wasassociatedwithimprovedmemoryofincongruentitems.Thesere- sultssuggestthatprefrontalandparietalbrainregionssupportcontrol processesandexertatop-downmodulationofhippocampusmediated memoryencoding,highlightingthehippocampusasacruciallinkbe- tweenresponseconflictresolutionandmemoryencoding.

In a series of studies, we recently investigated the role of the hippocampus in higher-order cognitivecontrolprocesses such asre- sponseconflictresolution.Wefoundthatin healthyparticipants,the left hippocampus isrecruited duringtheresolution of responsecon- flicts(Oehrnetal.,2015).Patientswithamesialtemporallobeepilepsy (MTLE)duetohippocampalsclerosishadanimpairedconflictresolu- tionperformance(Rammetal.,2020a).Inthesepatients,wefurtherob- servedareducedrecruitmentofthelefthippocampusthatcontributed tothedeteriorationinperformance(Rammetal.,2020b).Thesestud- iessuggestthatthehippocampusisindeedrequiredfortheresolution ofcognitiveresponseconflicts.However,whetherandhowtheseef- fectsrelatetothememoryfunctionofthehippocampusremainsunclear.

Specifically,itisstillanopenquestionwhetherhippocampaldysfunc- tioninMTLEpatientsaffectstheinteractionbetweenconflictresolution andmemoryencoding.

Here, we employed the previously established paradigm by Krebsetal.(2015)inMTLEpatientsandhealthycontrolstofurtherex- ploretheinteractionbetweenconflictresolutionprocessesandmemory encoding.First,wetestedwhetherstimulithatevokearesponseconflict aresubsequentlybetterrememberedthancontrolstimuliinadelayed incidentalmemorytaskandwhetherthiseffectdiffersbetweencontrols andMTLEpatients. Ifcognitivecontrolmechanismsrecruitedduring responseconflictresolutionpromote memoryencoding(Krebsetal., 2015) andMTLE patientsexhibit reduced conflictresolution performance(Rammetal., 2020b),onewouldexpectthemtoalsoshowa reducedmemorybenefitforconflictstimuli.Second,wetestedwhether brainregions recruited duringresponse conflictresolution predicted subsequentmemoryperformance.Inourpreviousstudy,wefoundin- creasedfunctionalcouplingbetweenprefrontalandparietalconflictpro- cessingregionsontheonehandandthemedialtemporallobeonthe otherhandinhealthyparticipants(Krebsetal.,2015)whichweinter- pretedasatop-down modulationof hippocampalmemoryencoding.

Inthepresentstudy,applyingthesameparadigminhealthycontrols andhippocampus-lesionedpatientsallowedustotestwhetherconflict processingspecificallyprovidedbythehippocampusfurthercontributes toimprovedsubsequentmemoryperformance.Wepredictedthatare- ducedconflict-inducedhippocampalrecruitmentduetomedialtempo- rallobedysfunctionaffectsthememorybenefitforconflictstimuli.We

furtherexploredwhetherfunctionalconnectivityofthehippocampus diﬀersbetweenMTLEpatientsandhealthycontrols.

2. Methods 2.1. Subjects

N=22patientswithMTLEaccordingtoInternationalLeagueAgainst Epilepsycriteria(Scheﬀeretal.,2017)participatedinthestudy.These patientsareidenticalwiththosefromourpreviousstudy(Rammetal., 2020b).Twopatientswereexcludedfrom thestudydue totheir ex- tremelylowaccuraciesintheStrooptask.Oneadditionalpatientdid not remember any faces andwas excluded aswell.The ﬁnalgroup consisted of 19 patients (age: 45.3± 14.7 years; 8 females;age at seizureonset:29.7±13.2years;diseaseduration:15.2±13.5years).

All patientsunderwentneurologicalexamination,EEG andstructural MRIaspartoftheirclinicaldiagnosticprocedure.BasedonEEGand seizure semiology,17 patientswerediagnosed withunilateralMTLE (leftMTLE:n =7;rightMTLE:n =10),twopatientshadabilateral MTLE.Ninepatientsreceivedantiepilepticdrug(AED)monotherapy,10 patientswereonpolytherapy(forAEDdosages,pleaseseesupplemental patientcharacteristicsinTableS1).Patientswithmultifocalepilepsy, comorbid neurologicaldiseases or severe psychiatric disorders were excluded.

Inadditiontopatients,n=19agematchedhealthycontrolspartic- ipatedinthestudy(age:45.8±13.5years;9females).Subjectswith aneurologicalorpsychiatricdisease,acentralnervoussystem-active medicationorcerebrallesionswereexcluded.

Allparticipantsgavewritteninformedconsent.Thestudywasap- provedbytheethicscommitteeoftheÄrztekammerWestfalen-Lippe andUniversityofMuenster(reference2016-004-f-S).

Asdescribed previously (Ramm etal.,2020b) thestructuralMRI scans received concordant evaluations by two radiologists follow- ing a standardizedprotocol toassess signs of hippocampalsclerosis (Dekeyzeretal.,2017).Healthysubjectsdidnotshowanysignsofhip- pocampalsclerosis.InMTLEpatients,radiologicalfindingsofindividual MRIscansaredescribedintheSupplementalResults(TableS1).Results ofthevolumetricanalysesconfirmedthequalitativefindingsofthera- diologistswithrespecttothelateralizationofthehippocampallesion (seeSupplementalResults,TableS3).

2.2. Experimentalprocedure

The participants underwent functional MRI scanning using an adaptedversionoftheface-wordStroopparadigmfromapreviousfMRI study(Krebsetal.,2015).Thisversionofthetaskfeaturedconﬂictand non-conﬂict trials,butnoneutraltrials(facesoverlaid withanunre- latedword)inordertoreduceoverallmemorydemandsforthissample includingpatients.

2.2.1. Familiarizationandtraining

PriortotheMRIsession,theparticipantsperformedafamiliariza- tion task for all face stimuli that were later presented in the face- word Strooptask.Apre-exposuretothestimuliofthefMRItaskap- peared necessary for two reasons. First, MTLE patients are signifi- cantlyimpairedinepisodicmemory(Helmstaedter,2002).Weaimed toavoidflooreffectsandmoreovertoequalizebaselinelevelssothat conflictmodulationcanbe observed.Second,asthereisanhabitua- tion of hippocampal responseto novelty (Murty et al., 2013), a fa- miliarizationphaseavoidsgroupdifferencesforthiseffect. Howpre- exposure may further affect interpretation will be addressed in the discussion.

Duringfamiliarization,thefacestimuliweredisplayedthreetimesin arandomizedorderfor2000mseachwithastimulus-onset-asynchrony (SOA)of3000ms.Thisprocedurewaschosentoavoideﬀectsofnovelty

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Fig.1.Face-wordStrooptaskandbehavioralresults.(A)Intheface-wordStrooptask,eachtrialconsistedofafaceoverlaidbythewords“man” and“woman” thatwereeithercongruentorincongruentwiththesexoftheface.ITI,inter-trialinterval.(B)Meanofresponsetimes(left)andmeanofresponsetimediﬀerences (right),overlaidwithsingle-subjectresults.(C)Meanoftheresponseaccuracies(left)andresponseaccuracydiﬀerences(right),overlaidwithsingle-subjectresults.

andflooreffectsduringthelatermemorytask.Toensurecontinuousat- tention,subjectshadtoindicate(vialeftvs.rightbutton-press)whether theyhadseenthecurrentfacebeforeornot.Stimuliwereshowninthe centerofawhitescreen,andablackfixationdotwaspresentedthrough- outtheentiretask.Afterfamiliarization,participantsperformed20sep- aratetrainingtrialsof theface-wordStrooptask.These stimuliwere differentfromthosepresentedinthefMRItask.

2.2.2. Face-wordStrooptask

The task comprisedface-word stimuliconsisting of maleand fe- malefaces[GlasgowFaceDatabase,Bruceetal.(1999)],overlaidby the words “man” or “woman” (in German language). These words could be either congruent or incongruent with the sex of the face (Fig.1A).Theparadigmconsistedofthe120faces(60malesand60 females)previously presentedin thefamiliarizationtask.Faceswere

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displayedfor1500msinthecenterofawhitescreen.Weusedanevent- relateddesigninordertoidentifyseparatetrial-relatedBlood-oxygen- level-dependent(BOLD)responses.Trialonsetsrandomlyvariedwith apseudo-exponentiallydistributedSOAof 5000ms(75%), 7500ms (17%)and10,000ms(8%).Thewordsweredisplayedinredinksuper- imposedonthefaces.Bothtrialtypeswerepresentedinarandomized orderandoccurredwithaprobabilityof50%.Subjectswererandomly assignedtooneoftwostimulussets.Stimulithatwerecongruentinone groupofsubjectswereincongruentintheothergroup.Subjectshadto indicatewhetherafacewasmaleorfemalebypressingtheleftorright mousebutton(buttonassignmentswerecounterbalancedacrosspartic- ipantsineachgroup).Throughouttheentireparadigm,ablackﬁxation dotwasdisplayedinthemiddleoftheface(andrightbelowtheword) toensureaccurateﬁxation.

2.2.3. Incidentalmemorytask

About 30–45 min afterthe face-word Strooptask, an incidental memorytaskoftothepreviouslyseenfaceswasconductedoutsideof theMRIscanner.All120facesthathadbeenshownintheface-word Strooptaskand40novelfaceswerepresentedinarandomorderona standardlaptopcomputer.Thefacesweredisplayedinthecenterofa whitescreenfor2000ms,followedbyaninter-trialintervalof2000ms (SOA=4000ms).Subjectswereaskedtoindicatewhethertheyhad seenthefacebefore(duringthefMRItaskorthefamiliarization)ornot bypressingoneoffourbuttons(4:“definitelyold”,3:“probablyold”, 2:“probablynew”,1:“definitelynew”).Wetestedwhetherthisrating scalewasuseddifferentlybyMTLEpatientsandhealthycontrolstoex- cludethepossibilityofstrategicdifferences.Inthesupplement,Fig.S1 showsthenumberofresponsesforeachresponsecategory,separately fortargetitemsanddistractoritemsaswellasforcontrolsandMTLE patients.InamultivariateANOVA,“group” (MTLEpatientsvs.controls) didnotaffectthenumberofresponsesforthedifferentresponsecate- gories(Pillai’sTrace;V=0.2,F(8,29)=1.0,p=0.45),arguingagainst adifferentialuseoftheratingscaleinbothgroups.

2.3. MRimageacquisition

MRimageswerecollectedusinga3TAchievaPhilipsMRscanner (PhilipsMedicalSystems,Best,NL)equippedwithasix-channelhead coil.During the face-wordStrooptask,a total of 294 T2^∗-weighted gradient echo-planar images (EPI) were acquired (TR = 2500 ms;

TE=35ms;36axialslices;interleavedacquisitioninascendingdirec- tion;FOV=230×230mm²;matrix=64×63;slice-thickness=3.6mm;

nointerslicegap;ﬂipangle=90°).Theﬁrst6volwerediscarded.The imagingvolumesweretiltedupwardsby15° fromtheAC-PC-planein ordertoreducedistortionsandsignaldropoutsintheanteriortemporal lobes.

Additionally, an anatomical 3D T1-weighted (T1w) turbo field echo (TFE) sequence (repetition time [TR] = 7.4 ms; echo time [TE] = 3.4ms; inversion time [TI] =900 ms; flip angle= 9°; 176 slices; matrix= 256×224;fieldofview [FOV]= 256×224mm²; slicethickness=1mm)wasacquired.Toinvestigatechangesinme- dialtemporallobestructures,paracoronalT2-weighted(T2w)images perpendiculartothe longaxisof the hippocampi wereacquiredus- ingaturbospinecho(TSE)sequence(TR =5196ms;TE=118ms;

parallelimaging factor[SENSE] =1.5; turbofactor= 26;38 slices;

FOV= 200×200mm²; acquisitionmatrix=372 ×312;slice thickness=2mm;slicegap=0.2mm).

2.4. Dataanalysis

2.4.1. Behavioraldata

Meanresponsetimes(RT),includingonlycorrectresponses,andac- curacyofresponsesintheface-wordStrooptask wereanalyzedwith two-waymixedanalysesofvariances(ANOVAs)with“congruency” (in-

congruentvs.congruent)asawithin-subjectfactorand“group” (healthy controlsvs.MTLEpatients)asabetween-subjectsfactor.

Memoryperformancewasanalyzedasfollows.First,wesoughtto replicatethepreviousfindingofconflict-enhancedmemory.Asinour previousstudy,wecontrastedthenumberof“definitelyold” (remembered)withallotherratings(forgotten)fortargetstimuli,reflectinga highconfidentrecognition measure(putativelymainlybasedonrec- ollection).Inanadditionalanalysis,wecountedpreviouslypresented stimuliratedaseither“definitelyold” or“probablyold” asremembered, andfacesratedas“probablynew” and“definitelynew” asforgotten,re- flectingamoreglobalmeasureofbothrecollectionandfamiliarity.We alsoassessedfalsealarmrates(distractoritemsratesas“definitelyold” or“probablyold”).Inallanalyses,two-waymixedANOVAswerecon- ductedtoinvestigatemaineffectsofcongruencyandgroupaswellas theirinteraction.

We additionally analyzed response times for remembered target stimuli(“deﬁnitelyold” and“probablyold”).Theseresultsarepresented inthesupplement.

WealsotestedforcorrelationsbetweenStrooptaskperformanceand retrievalratesusingnon-parametricKendall’stau,asthisparameteris particularlysuitableforsmallgroupsanalyses.Wecorrectedformul- tiplecomparisonsusingBonferronicorrection(p-value/2).Theresults arepresentedinthesupplement.

2.4.2. FMRIdatapreprocessingandanalysis

ThefMRIdatawerepreprocessedandanalyzedwithStatisticalPara- metric Mapping(SPM12; UniversityCollege, London, UK) usingthe sameprocedureasappliedpreviously(Rammetal.,2020b).Inshort, functionalEPIswererealigned,normalized,reslicedandsmoothedus- ingaGaussiankernelwith8mmFWHM.Weveriﬁedtheaccuracyof normalizationinpatientswiththegreatestabnormalitiesinthemedial temporallobe.Correctionofnormalizationparameterswasnotneces- sary.

Basedonoura-priorihypothesisthatconflict-inducedmemoryim- provementisdirectlymediatedbyhippocampalrecruitment,inthefMRI analysis,wefocusedontheeffectsofcongruencyandtheinteraction betweencongruencyandmemorywithinahippocampalROI.Ifsignifi- cant,wefurtherreportmaineffectsofmemoryandgroupaswellasthe interaction“congruencyxmemoryxgroup”.Tonotmissanyeffectsout- sidethehippocampus,wealsotestedfortheseeffectsinawhole-brain analysis.

Infollow-upanalyses,weextractedbeta-valuesfromsigniﬁcantacti- vationclustersandperformedwithinandbetweengroupcomparisons, respectively. Pleasenotethatsuchpost-hoccomparisonsarenotcor- rectedformultiplecomparisons.Theyarepresentedforillustrativepur- posesandtheydonotallowinferences.

Theﬁrstlevelgenerallinearmodel(GLM)includedfourregressors (andtheirtemporalderivates)relatedtotheexperimentalconditions andsixmovementregressorsderivedfromtherealignmentprocedure.

Duetotheoverallhighmemoryperformance,theexperimentalcondi- tions(congruent,incongruent)weredividedintotrialswithfacesthat wererecollectedwithhighconﬁdencevs.facesthatwerenotrecollected withhighconﬁdence.

Thus, in the fMRIanalysis, we contrasted stimulirated as “definitely old” with allotherratings,correspondingtoanfMRImeasure thatisputativelymainlybasedonrecollection,asinourpreviousstudy (Krebsetal.,2015).Inthesupplement,wealsoreportfMRIresultsbased onfirst-levelmodelsinwhichwecontrastedremembered(“definitely old” and“probablyold”)withforgotten(“probablynew” and“definitely new”)items.

First-levelindividualcontrastimagesforeachofthefourexperimen- talconditionswereenteredintorandom-effectssecond-levelanalyses forthetwogroups(healthycontrolsvs.MTLEpatients).Weappliedflex- iblefactorialdesignstoinvestigatemaineffectsof“congruency” (incongruentvs.congruent),“memory” (recollectedwithhighconfidencevs.

notrecollectedwithhighconﬁdence)andtheinteraction(congruency

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xmemory)withineachgroup.Additionally,thecontrastimagesfrom controlsandMTLEpatientswereenteredintoacommonGLM(ﬂexible factorialdesign)totestforamaineﬀectof“group” andforinteractions ofthetwowithin-subjectfactors“congruency” and“memory” withthe between-subjectsfactor“group” (groupxcongruency,groupxmemory).

Voxelactivationswereidentiﬁedataninitialcluster-formingthresh- oldofp<0.001andfamily-wiseerror(FWE)correctedformultiplecom- parisonsattheclusterlevel(forwhole-brainanalyses)oratthevoxel- level(forhippocampalROIanalyses),respectively.Inthehippocampal ROIanalysis,weperformedsmallvolumecorrectionforaROIcontain- ingleftandrighthippocampusasdeﬁnedbytheAutomaticAnatomic Labeling(AAL)atlas(Brett,2002).Inthisanalysis,MTLEpatientswith amygdalohippocampectomywereexcluded.Fortheinterpretationofac- tivations,wesubdividedthehippocampusintoananterior(Y≥-21mm MNI)andaposterior(Y≤-22mmMNI)part(Poppenketal.,2013).

2.4.3. Functionalconnectivityanalyses

We performed exploratory functional connectivity analyses using the CONN toolbox V18.b (www.nitrc.porg/projects/conn, RRID:SCR_009550).Functional imageswerepreprocessedusing SPM andcorrectedfornoiseusingthedefaultdenoisingpipeline(Whitfield- GabrieliandNieto-Castanon,2012).Inadditiontotemporalband-pass filtering (0.008– 0.09Hz),theprocedure includedlinearregression of confoundingfactors, i.e. effectsof no interestfromwhite matter, cerebrospinalfluidandmovements(realignmentparameters).

Thefunctionalconnectivityanalysiswasaseed-basedconnectivity measure(seedtovoxel)basedonbivariatecorrelationalanalysesdur- ingthetask(averagingcongruentandincongruenttrials).Wechosetwo anatomicalseedregions,i.e.leftandrighthippocampus,basedonthe ROIintheunivariateanalysis.First-levelconnectivitymapsrepresent- ingz-transformedcorrelationcoeﬃcientsintheBOLDsignalbetween theseedandeachvoxelinthebrainwereenteredintoasecond-level ANOVA,allowingustoinvestigatediﬀerencesofhippocampalconnec- tivitybetweenMTLEpatientsandcontrols.Thestatisticalthresholdwas identicaltothatusedintheunivariatefMRIanalysis(i.e.p<0.05;FWE- correctedattheclusterlevelwithaninitialcluster-formingvoxelthresh- oldof p<0.001).Analysisandresults ofregionalbrainvolumesare describedinthesupplement.

2.5. Dataandcodeavailability

Group-levelstatisticalmapsareaccessibleunderthefollowinglink:

https://identiﬁers.org/neurovault.collection:8706.Behavioraldatacan bemadeavailableviadatasharingagreementuponrequesttothecor- respondingauthor.

Softwareusedinthisstudyisopenlyavailable.

3. Results

3.1. Behavioralresults

3.1.1. Face-wordStrooptask

TheresultsoftheStrooptaskareshowninFig.1B,C.

WithrespecttoRT,amixedANOVA revealedsigniﬁcantmainef- fectsof“congruency” (incongruentvs.congruent;F(1,36)=44.3;p<

0.001)and“group” (MTLEpatientsvscontrols;F(1,36)=4.7;p=0.037) aswellasasigniﬁcantinteraction(groupxcongruency;F(1,36)=4.6;

p=0.039). RTslowinginincongruentcompared tocongruenttrials wasfoundinbothhealthysubjects(t(18)=−5.4;p<0.001)andMTLE patients(t(18)=−3.9;p=0.001),conﬁrmingrobustinterferenceef- fectsinourparadigm.ComparingpatientswithleftMTLEandpatients withrightMTLE,amixedANOVAdidneitherrevealamaineﬀectof group(F(1,15)<0.001;p=1.0)noraninteraction(groupxcongruency;F(1,15)=0.01;p=0.9).

Forresponseaccuracy,amixedANOVAshowednosigniﬁcantmain eﬀects (congruency:F(1,36) = 0.5; p = 0.46; group: F(1,36) = 2.5;

p=0.12)orinteraction(groupxcongruency;F(1,36)=0.5;p=0.51).

AmixedANOVAcomparingleftandrightMTLEpatientsdidnotyield asigniﬁcantmaineﬀectofgroup(F(1,15)=0.4;p=0.6).

Insum,inbothgroups,responsesweresignificantlyslowerinincon- gruenttrialswhileaccuracywasunaffected.Theresultsindicatecon- flicteffectsinbothcontrolsandMTLEpatients,providingthebasisfor testingwhethermemoryperformanceismodulatedbyconflict-related controlprocesses.

3.1.2. Incidentaldelayedmemorytask

RetrievalratesarepresentedinFig.2.Beforeanalysis,weexcluded allerrortrialsandmissesintheface-wordStrooptask.Thenumberof analyzeditemsdidnotdifferbetweencontrols(97%)andMTLEpatients (93%;t(36)=1.79;p=0.082).Notably,falsealarmrates(newfaces ratedas“definitelyold” or“probablyold”)didnotdifferbetweenMTLE patients(33%)andcontrols(34%;t(36)=0.1;p=0.9).

Wefirsttestedwhetherstimuluscongruency(incongruentvs.congruent)influencedthenumberofhighconfidentrecognitionresponses fortargetstimuli,i.e.,facesratedas“definitelyold”.AmixedANOVA yieldedasignificantmaineffectof“group” (healthycontrolsvs.MTLE patients;F(1,36)=7.0;p=0.012)andatrendforaninteraction(group x congruency; F(1,36)= 3.0;p= 0.092)butnosignificant mainef- fectofconflict(F(1,36)=0.2;p=0.9).Thus,MTLEpatientsreached lowerhighconfidentrecognitionscoresthanhealthycontrols.Thiswas trueforbothcongruent(t(18)=2.1;p=0.046)andincongruenttri- als(t(18)=3.2;p=0.003).Withingroups,highconfidentrecognition scoresdid notdifferbetweencongruentandincongruenttrialsinei- thercontrols(t(18)=−1.3;p=0.21)orMTLEpatients(t(18)=1.2;

p=0.25).Retrievalratesdidnotdiﬀerbetween rightandleftMTLE patients(maineﬀectofgroup:F(1,15)=2.6;p=0.13)andwereinde- pendentofcongruency(interaction:F(1,15)<0.1;p=0.8).

Inacomplementaryanalysis,stimuliwerecountedasremembered when rated aseither“definitelyold” or “probablyold” (reflecting a low confidence recognitionmeasure andpossiblyreflecting familiar- ity).Inamixed ANOVAofthismoreglobalmemorymeasure,MTLE patients reached lower scores (main effect of group; F(1,36)= 6.6;

p=0.015)andtheinteractionbetween“group” and“congruency” was signiﬁcant (F(1,36)= 5.0;p= 0.032).This indicatesthatword con- gruencymodulatedmemorydiﬀerentlyinhealthycontrolsandMTLE patientswhenconsideringamoreglobalmeasureofmemory.Specif- ically, healthycontrols showedimproved retrievalof faces from in- congruentcomparedtocongruenttrialsinhealthycontrols(81.6%vs.

77.6%;t(18)=−2.5;p=0.021).Bycontrast,MTLEpatientsdidnotshow suchmemorybeneﬁtofincongruentstimuli(65%vs.66%;t(18)=−0.7;

p=0.5).Inincongruenttrials,retrievalratesweresigniﬁcantlyhigher for controlsthanMTLE patients(t(38) =3.0; p=0.005), whilethis diﬀerence only reacheda trend for congruent trials (t(30.5) = 2.0;

p=0.052).

Insum,incongruentdistractorwordsintheface-wordStrooptask causedtypicalbehavioralcostsintermsofRTslowinginbothhealthy controlsandMTLEpatients,butfamiliarity-basedrecognitionscoresin- creasedduringconﬂictonlyinhealthycontrols.

3.2. FMRIresults

3.2.1. Maineﬀectofcongruency

ROIanalysisinthehippocampus:Inlinewithourmainhypothesisand previouswork(Oehrnetal.,2015;Rammetal.,2020b),wefirstana- lyzedcongruencyeffectsinaROIconsistingofbilateralhippocampus.In healthycontrols,wefoundasmallbutsignificantactivationincreasefor incongruentvs.congruenttrialsinbothleftposteriorhippocampus(MNI

−30/−24/−16,Z=3.74,p(FWE)=0.036;clustersize=1)andright posteriorhippocampus (MNI28/−36/−4,Z=3.72,p(FWE)=0.038;

clustersize=1).Noeﬀectinthereversedirectionwasobservedinthe hippocampus.InMTLEpatients,thesameanalysisdidnotrevealamain eﬀectofcongruencyinthehippocampus.InamixedANOVAwithMTLE

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Fig.2. Behavioralresultsoftheretrievaltask.(A)Distributionofretrievalratings.(B)Relativeretrievalrates(“deﬁnitelyold” and“probablyold”)anddiﬀerence scores(incongruent-congruent),overlaidwithsingle-subjectresults.

Table1

Activationclustersincontrols(maineﬀectofcongruency).

Brain region Voxels Peak voxel Coordinates (x,y,z) FWE-corrected cluster p -value R Anterior Insula 5832 32 20 − 6 < 0 .001 L Anterior Insula 640 − 26 22 − 10 < 0 .001

R SMA 2841 2 16 48 < 0 .001

L Caudate Nucleus 188 − 10 16 − 2 0 .018

L Precuneus 690 − 18 − 74 30 < 0 .001

L MFG 374 − 48 26 30 < 0 .001

L Precentral Gyrus 277 − 48 2 46 0 .003

L Putamen 157 − 32 − 2 − 10 0 .038

MNI,MontrealNeurologicalInstitutesystem;L,lefthemisphere;R,righthemisphere;FWE,family-wise error;SMA,supplementarymotorarea;MFG,middlefrontalgyrus.

patientsandcontrols,wedidneitherﬁndmaineﬀectsofcongruencyor groupnoraninteraction(groupxcongruency)withinthehippocampus ROI.

Whole-brainanalysis:Inhealthycontrols,wefoundseveralsigniﬁ- cantclustersofincreasedactivityduringincongruenttrials(including bilateralinsula,bilateralsupplementarymotorareaandcingulatecor- tex,leftprecentralgyrus,bilateralmiddlefrontalgyrus,precuneus,cau- datenucleus,leftputamen;Table1,Fig.3A).Noclustersshowedare- verseeﬀect.Theseclusterslargelyreplicateresultsofourpreviousstudy

(Krebsetal.,2015)andaretypicalﬁndingsincognitivetasksthatre- quirebehavioralinhibition(Niendametal.,2012).

InMTLEpatients,thesameanalysisdidnotyieldanysigniﬁcantacti- vationclusters.AmixedANOVAincludingcontrolsandpatientsshowed asigniﬁcantgroupxcongruencyinteractionintheprecuneusspread- ingtothePCC(MNIpeakcoordinates:−4/−58/38;clustersize=182;

p(FWE)=0.048;Fig.3B).Thisinteractionindicatesareducedconﬂict- induced activation increase in MTLE patients compared to controls.

Post-hocpairedt-testsinthisinteractionclustershowedincreasedacti-

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Fig.3. Wholebrainanalysisofactivationsrelatedtoresponseconﬂict.(A)Re- sultsinhealthycontrolsforthemaineﬀectofcongruency(incongruent>con- gruenttrials).(B)Resultsfortheinteraction(groupxcongruency).Activations arepresentedwhensurvivinganFWE-correctedclusterthresholdofp<0.05.

Initialcluster-formingthresholdwassettop<0.001.(C)Correspondingcon- trastestimatesfortheinteractioncluster.Errorbarsshowstandarderrorofthe mean.

vationduringincongruentrelativetocongruenttrialsinhealthysubjects (t(18)=−4.5;p<0.001)butnotinMTLEpatients(t(18)=1.1;p=0.27;

Fig.3C).

Insum,wefoundconﬂict-relatedactivationsinanextendedfron- toparietalnetworkinhealthycontrolsandreducedeﬀectsinMTLEpa- tients.

3.2.2. Subsequentmemoryeﬀects

ROIanalysisinthehippocampus:Inhealthycontrols,wedidnotob- servea signiﬁcantmaineﬀectofmemoryin bilateralhippocampiin anANOVAwiththewithin-subjectfactors“congruency” (congruentvs.

incongruent)and“memory” (recollectedwithhighconfidencevs.not recollectedwithhighconfidence).Interestingly,however,wefounda significantcongruency xmemoryinteractionwith apeak inthe left posteriorhippocampus(MNIpeakcoordinates−32/−24/−16;Z=3.81;

p(FWE)=0.028;clustersize=4;Fig.4A),spreadingintoanteriorhip- pocampus(max/minY(mm):−20/−24).Thiscluster,whichcomprises onlyvoxelssurvivingvoxel-levelFWE-correctionwithinthehippocam- pal ROI,wasdirectly adjacenttothe areawherewefound conﬂict- relatedactivationincrease(MNIpeakcoordinates:−30/−24/−16).

Post-hocpairedt-testsoftheextractedbetavaluesrevealedapositive subsequentmemoryeffectforcongruenttrials(t(18)=2.4;p=0.029), but,somewhatsurprisingly,thereversepatternforincongruenttrials (t(18)=2.3;p=0.033),withhigheractivationsforlaterforgottenas comparedtorememberedincongruentfaces(Fig.4B).InMTLEpatients, neitherthemaineffectofmemorynortheinteraction(congruencyx memory)revealedsignificantactivationswithinthehippocampalROI.

In sum, in controls, hippocampal activationwas associated with greater memorybeneﬁtsforfacesfromcongruent trialscompared to facesfromincongruenttrials.

Whole-brain analysis: Wenext tested whetherotherbrain regions werepredictiveofmemorysuccess.Inhealthycontrols,thewhole-brain analysisdidnotrevealanyactivationclusterwitheitheramaineﬀect ofmemoryoraninteraction(congruencyxmemory).

InMTLEpatients,wefoundanactivationclustercomprisingthePCC andtheprecuneus(MNIpeakcoordinates:0/−52/22,clustersize=182, p(FWE)=0.022,Fig.4C)thatshowedamaineﬀectofmemorybutno interactionwithcongruency.

Post-hoct-testsoftheextractedbetavaluesrevealedthatactivation wasincreasedduringencodingoflaterrememberedcomparedtoforgot- tenfacesfrombothcongruent(t(18)=2.9p=0.01)andincongruent trials(t(18)=3.7p=0.002;Fig.4D).

The results indicate thatthe PCC/precuneuscontributed tolater memorysuccessinMTLEpatientsindependentofcongruency.

3.3. Functionalconnectivityresults

Weinvestigatedfunctionalconnectivitybetweenactivationsinhip- pocampalseedsandeachvoxelinthebrain.Forthelefthippocampal seed,functionalconnectivity(overtasks)didnotdiﬀerbetweengroups.

However,MTLEpatientsshowedsigniﬁcantlydecreasedcouplingbe- tweenrighthippocampusandrightPCCcomparedtohealthysubjects (MNI12/−44/30;clustersize=197,p(FWE)=0.004;Fig.5).Theanal- ysisdidnotrevealasigniﬁcantinteraction(groupxcongruency).

4. Discussion

WeinvestigatedhowhippocampallesionsinMTLEpatientsaffect theimpactofconflictresolutiononmemoryencodingatabehavioral level and atthe level of BOLDresponses. Using apreviously estab- lishedface-wordStroopparadigmandanincidentalmemorytask,we testedwhethertheconflict-inducedmemorybenefitthatwehadfound inhealthysubjects(Krebsetal.,2015)wasreducedinMTLEpatients.

Moreover,weinvestigatedwhetherrecruitmentofthehippocampusor otherconflict-relatedbrainregionsisnecessaryforamemorybenefitof conflictstimuli.

WhilebothMTLEpatientsandhealthycontrolsshowedbehavioral costsofconflictprocessingintheStrooptask,onlyhealthycontrolsex- hibited improvedmemoryfor incongruentitems.Conflict processing wasassociatedwithactivationofbilateralhippocampus,precuneusand PCCin healthycontrols.Conflict-related activationof precuneusand PCCwassignificantlyreducedinMTLEpatientscomparedtocontrols.

Furthermore,activationofprecuneusandPCCinsteadpredictedsubse- quentmemoryinMTLEpatients.Interestingly,inhealthycontrols,left hippocampalactivationwaslessefficientformemoryencodingincase ofconflictcomparedtonon-conflict,aseeminglycounterintuitiveacti- vationpattern.

In contrast to the auditory Stroop task in our previous studies (Ramm et al., 2020a, 2020b), in the face-word Stroop task, MTLE patientsshowed normalresponseaccuracyandincreasedRTin con- gruentbutnotincongruenttrials.Thisdiscrepancymayberelatedto the difference between thetasks: Compared tonaming thepitch of a tone(as inourprevious study),decisionsonthesexof aface are morecomplexandrequireintegratingvariouskindsofinformation.As Krebsetal.(2015)alreadystated,thismighthaveattenuatedeffectsof conflictonbehavioralmeasuresandalsoexplainwhythepresentresults donotperfectlymatchwithourpreviousfindings.

Previousstudiesfoundthattheprocessingofincongruentitemsim- provedsubsequentmemory(Krebsetal.,2015;Rosneretal.,2015).Re- cently,Jimenezetal.(2020)showedthatmemorywasonlyenhanced forthoseincongruentitemsthatwerepresentedafteranotherincongru- enttrial.Thesecontradictoryfindingsmightbeexplainedbydifferent trialordersofcongruentandincongruenttrialsand/ordifferentStroop

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Fig. 4.BOLD activityrelated tosubsequent memory performance. (A) Results (FWE- corrected)forthe “congruency” x “memory” interaction within a hippocampal mask in controls.(B)Correspondingcontrastestimates forthe hippocampalinteraction cluster. (C) Results of the main eﬀect of memory on whole-brain activation in MTLE patients.

Activationsare presentedwhensurviving an FWE-correctedclusterthresholdof p<0.05.

Initialcluster-formingthresholdwassettop

<0.001.(D)Correspondingcontrastestimates fortheFWE-correctedPCC/precuneuscluster inMTLEpatients(top)andcontrols(bottom).

Errorbarsshowstandarderrorofthemean.^∗ signiﬁcant(p<0.05).

trialsthatwereselectedforthelatermemorytask.Inthepresentstudy, thebehavioralresultsinhealthyparticipantsindicateamemorybenefit forincongruentitems,butonlywhenadaptingamoreglobalmemory measureincludinghighandlowconfidentrecognition.Thus,conflict- inducedmemorybenefitseemstodependontaskfeaturessuchastrial compositionorwhichkindofrecognitionmeasureisused.

Importantly,nosuchmemorybeneﬁtwasfoundinMTLEpatients.

Morespecifically,MTLEpatientsshowedreducedmemoryparticularly forincongruentitems.Aswe foundimpairments ofresponseconflict resolutionduringanauditoryStrooptaskin anMTLEpatientcohort largelyoverlappingwiththecurrentsample(Rammetal.,2020b),one mayassumethatthedecreasedmemorybenefitrelatestoreducedcon- flictresolutionperformanceofpatients.

Basedonourpreviousfindingofareducedconflict-relatedlefthip- pocampusrecruitmentinMTLEpatients(Rammetal.,2020b),wehy- pothesizedthatthehippocampusitselfmightcontributetoimproved memoryencoding of incongruent items.Indeed, we found asignifi-

cant interactionbetween memory andcongruency in the left posterior hippocampus inhealthycontrols.However,hippocampalactiva- tionwasactuallylesspronouncedforencodingitemsfromincongruent trialscompared tocongruenttrials. This clusterwas closetothere- gionshowingconflict-relatedactivationinthisstudyaswellasinour previous studythatused anauditoryStroopparadigm(Rammetal., 2020b). This suggeststhat recruiting thehippocampus for the reso- lution ofresponseconflictsinterfereswithitsrolein memoryformation. This findingwas unexpectedsince previousfMRI results found posteriorhippocampalrecruitmentduringencodingofrepeatedstim- uli (Poppenketal., 2010).One explanationmightbe thatitreflects a competition for limited resources between two functions that are both hippocampus-dependent. A similar competition for neural resources inprefrontalcortex haspreviouslybeensuggested asan ex- planationforlowermemoryencodingduringademandingsecondary task (Reynolds etal.,2004).Furthermore, convergingevidencefrom animallesionstudiesandhumanfMRIrecordingssuggestthatmultiple

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Fig.5. Resultsoffunctionalconnectivityanalysisfortherighthippocampal seed.Diﬀerencesinfunctionalconnectivityoftherighthippocampusbetween controlsandMTLEpatients.Thecolorbarrepresentst-values.Yellowareasindi- catesigniﬁcantlyincreasedfunctionalconnectivitywiththerighthippocampal seedincontrolscomparedtoMTLEpatients.Clustersarepresentedwhensur- vivingafamily-wise-errorcorrectedclusterthresholdofp<0.05.Initialcluster- formingthresholdwassettop<0.001.Theleftsideoftheimagescorresponds totheleftsideofthebrain.MTLE,mesialtemporallobeepilepsy.

simultaneouslyactivatedmemorysystemsinteractinabidirectionally competitiveway(Poldrack andPackard,2003).Forexample,disrup- tionofhippocampalfunctioninrodentsenhancedstriatalinstrumental learning(McDonaldandWhite,1993;Packardetal.,1989).Thetheory ofahippocampalcompetitionisalsoinlinewithhumanneuroimaging studiesshowingthatthetypeofrepresentationthatisusedformemory orspatialnavigation (hippocampalorstriatal mediated)aﬀects both performanceandactivation(Hartleyetal.,2003;Poldracketal.,2001).

Alternativeexplanationsforthecounterintuitiveactivationpattern inthehippocampusshouldbetakenintoaccount.Consideringthatpar- ticipantshadperformedafamiliarizationtaskbeforethemainexperi- ment,itmightbeplausiblethattheydidnotonlyencodeinformation duringtheStrooptaskbutalsoretrievedthepreviouslypresenteditems, leadingtoacompetitionbetweenencodingandretrieval.Thisnotion issupportedbyevidencesuggestingthatencodingandretrievalcan- notoccuratthesametimeand,again,competeforlimitedresources (Huijbersetal.,2009;ReasandBrewer,2013).Thus,anincreasedre- cruitmentofthe posteriorpartof thehippocampusmight reﬂect re- trievalsuccess(Eichenbaumetal.,2007),leadingtoreducedmemory encoding.Thisinterpretationwouldbeinlinewiththenotionthaten- codingoffamiliarorrepeatedstimuli(possiblyduetoaretrievalcom- ponent)morestronglyreliesonposteriorhippocampus(Greiciusetal., 2003;Kim,2015;Poppenketal.,2013).Nevertheless,sincehealthysub- jectsshowedanimprovedmemoryforconﬂict-relatedstimuli,neural activityinotherbrainregionsmusthavehadanevengreaterimpacton memoryencoding.

Wefurthertestedwhetheractivationofother,possiblyconnected, brainareascouldaccountforthebehavioralresults.Healthycontrols exhibitedconflict-relatedactivationclustersinprefrontalandparietal brainregions, largely in line with theresults of our previous study (Krebsetal.,2015).Morespecifically,activationsinthelateralandme- dialPFCarethoughttomediateconflictmonitoringandconflictres- olution(Botvinick etal.,2001; Oehrnetal.,2014).Fromanetwork perspective,controls’bilateralactivationintheanteriorinsulasuggest aninvolvementofthesaliencenetwork(Uddin,2015).Thismightrep- resenttheneuralsignalwhichinitiatesaswitchfromdefaultmodeac-

tivity tocognitivecontrolactivity(Sridharanetal., 2008).Posterior midlineregions,particularlytheprecuneus,arealsoinvolvedincogni- tivecontrolprocesses,probablythroughtheirroleindirectingattention (CavannaandTrimble,2006;LeechandSharp,2014).Conflict-related activationintheprecuneusandpartlythePCCwassignificantlyreduced inMTLEpatients.Notably,thesefunctionalchangesintherecruitment ofprecuneus/PCCofMTLEpatientswerenotreflectedbyvolumetric changesintheseareas(seeSupplementalResults,TableS3).Theresults arelargely inline, however,withourfunctionalconnectivityresults thatrevealeddecreasedcouplingbetweentherighthippocampalseed andrightPCC(Fig.5).Thisfindingisconsistentwithpreviousstudies showingextratemporal functionalchangesin MTLEpatients,particu- larlyinregionsinvolvedinthedefaultmodenetwork(DMN;Laufsetal., 2007;Waitesetal.,2006),and,morespecifically,adecouplingbetween hippocampusandotherpartsoftheDMN(Liaoetal.,2011;Pittauetal., 2012;Zhangetal.,2010).

The reduced effects of congruency mainly in the precuneus and partlythePCCinMTLEpatientscomparedtohealthycontrolsarein linewiththebehavioralfindingthatcongruencymodulatedmemory performanceincontrolsbutnotinMTLEpatients.However,canfunc- tionalchangesintheprecuneus/PCCindeedexplainthereducedmem- orybenefitforconflictstimuliinMTLEpatients?Precuneusandalso PCChavebeensuggestedtobecorenodesoftheDMNwhichisactive intheabsenceofataskandassociatedwithinternallydirectedcogni- tion(FranssonandMarrelec,2008).Incontrast,otherstudiesargued againstaninvolvementoftheprecuneusintheDMN(Buckneretal., 2008;Marguliesetal.,2009).Itislikelythatthereisafunctionaldif- ferentiationwithinprecuneusandPCC.Whereastheventralprecuneus andventralPCC(correspondingtoBrodmannareas29/30)showsin- tegrationintheDMN,thedorsalprecuneus(orBrodmannarea7)and dorsalPCCaremorestronglyrelatedtobrainareasofmotorexecution andcognitivecontrol(Leechetal.,2011;ZhangandLi,2010,2012).In MTLEpatients,functionalchangesintheprecuneusdidnotshowclear restrictiontoeitherventralordorsalprecuneus.Thus,interpretationon theleveloffunctionalnetworksseemsequivocal.Instead,thereiscon- vincingevidenceforacrucialroleoftheprecuneusinepisodicmem- ory(Berryhilletal.,2007;Dorfeletal.,2009;Lundstrometal.,2005; Richteretal.,2016;RuggandVilberg,2013).Theideathattheroleof theprecuneusinepisodicmemoryexplainsthereducedconflict-related memorybenefitinMTLEpatientsisinlinewiththefindinginourprevi- ousstudythattheprecuneuswaspredictiveofaconflict-inducedmem- orybenefit(Krebsetal.,2015).Moreover,andmost importantly,we foundadistinctactivationclustercomprisingpartsofthePCCandthe precuneuswhichpredictedretrievalsuccessindependentofcongruency in MTLEpatients. Notably,theprecuneusismorestronglyrelatedto memoryretrieval(Lundstrometal.,2005)whichisinlinewiththeidea thatsubjectsdidnotonlyencodebutalsoretrievedthefacestheyhad beenfamiliarizedbefore.Functionalimpairmentintheprecuneusdue tohippocampaldamagemightreflect(presumably)maladaptivereor- ganizationofmemoryprocessesfromhippocampustoposteriormidline regions which mightcontributetoepisodic memoryimpairmentand deficitsintheirmodulationbycognitivecontrol.Thisislargelyinline withapreviousstudyshowingthatfunctionalchangesintheposterior cingulumwererelatedtomemoryperformance(Doucetetal.,2013).

Wespeculatethatdue tochangesin precuneusrecruitment, memory recallwasnotmodulatedbycongruencyinMTLEpatients,leadingto similar(additional)encodingeﬃciencyinbothtrialtypes.

Fromabroaderperspective,thepresentfindingsarerelevantwith regardtoarelatedresearchlineonhippocampalinvolvementduring approach-avoidanceconflicts(forreview,seeItoandLee,2016).For instance,ithasbeenshownthatbehavioraladaptationsinanapproach- avoidanceconflictparadigm,andinparticulartheavoidanceofthreats, was associated with larger activity in the anterior hippocampus of healthyparticipants(Bachetal.,2014).Crucially,behavioraladapta- tionwasimpairedinTLEpatients,andthisdidnotmerelyreflectgen- eral memoryimpairments (basedonneuropsychological assessment).

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Moreover,inarecentstudy,patientswithamesialtemporallobele- sionwereimpairedinapproach-avoidancedecision-makingbutshowed recollectionofthreatmemorysimilartocontrols(Bachetal.,2019).

Thesefindingssuggestthathippocampalinvolvementduringapproach- avoidanceconflicttasksisnotnecessarilyrelatedtomemory.Inhow farhippocampalactivityduringtheseparticularconflictsisdirectlycon- tributingtolong-termmemoryis,however,amatterofdebate.Specifi- cally,arecentbehavioralstudy(Chuetal.,2020)didnotfindmemory improvementsinanapproach-avoidanceconflicttask.Thisisnotonly challengingtheaboveview,butisalsoinconsistentwithourprevious (Krebsetal.,2015)andcurrentfindingsintheface-wordStrooptask.

AsdiscussedbyChuetal.(2020),thisbehavioraldiscrepancymightbe explainedbydifferencesinthetaskdesign(i.e.,presencevs.absenceof incentivevalence;associativevs.itemmemory)andaceilingeffectdue topre-exposure.Moreover,theinterpretationofhippocampalinvolve- mentinapproach-avoidanceconflicttasksiscomplicatedbytheincen- tivevalencedimension,whichis knowntomodulatememoryforma- tionviathehippocampus(ShohamyandAdcock,2010).Together,the diversesetofresultsacrossdifferentstudiesanddomainssupportthe notionthatthehippocampushasaroleinboth(approach-avoidance) conflictprocessingandconflict-basedmemoryformation,buttheexact relationshipbetweentheseprocessesseemstodependonthenatureof theparadigm.Inthelightofthisdiscussion,ourobservationthathip- pocampallesionsabolishconflict-inducedmemoryimprovementsmight indicate thatan activehippocampus duringconflictprocessing indi- rectlyenhancesmemoryencodingbyallowingtheconflict-relatedre- cruitmentofotherbrainregions,suchastheprecuneus.

In the present study, we found reduced BOLD signal in several brainregions in MTLEpatients. Aspatients showedalteredconﬂict- modulationofmemory,weinterpretedchangesoftheactivationpattern asadysfunctionalprocess.Thisisinlinewiththemajorityofprevious studiesshowingthatactivationchangesrepresentapathologicalprocess oranineﬃcientcompensatoryattemptinTLE(Vlooswijketal.,2010).

ThesituationisevenmorecomplexbecausetheBOLDsignaldepends onneurovascularcouplingbetweenneuralactivityandbloodoxygena- tion(andvolume),andthiscouplingmaybesubstantially alteredin epilepsy.Specifically,inepilepsypatients, interictalepileptiformdis- chargescan affecttheBOLDsignalandthuslead todeviations from linearityinneurovascularcoupling(Vogesetal.,2012;Watanabeetal., 2014).Inourstudy,wereducedtheimpactofthisconfoundbytesting thegroupdifferencesintherelativeactivationsbetweentwoconditions (congruentvs.incongruent).Nevertheless,futurestudieswhichallow foradirectmeasurementof neuralactivitysuchasintracranialEEG recordingsshouldbeconductedwiththesameparadigm,ideallyafter runningtheexperimentviafMRIbeforeelectrodeimplantation.

Our studyhas several limitations. Our mainbehavioral outcome measuresoftheStrooptaskwereRTandaccuracywhichweanalyzed separately.TheresultsshowthatRTwasclearlymodulatedbyconflict, whileaccuracywasnotaffected(ceilingeffect),neitherincontrolsnor in patients.This indicatesthat thepresentconflictmanipulationdid notevokeasubstantialnumberofresponseerrors(areflectionofau- tomaticresponsecapturebytheirrelevantstimulus),butledtosignifi- cantlyprolongedRTs(areflectionofcognitivecontrolprocessestopre- ventresponseerrors).Thelowerrorratemightberelatedtothefairly simpletwo-alternativechoice(insteadoffourresponsesintheregular Strooptask),andtheprocessingofsuperimposedgenderlabelsmight notbeas“automatic” ascolor-wordreadingintheregularStrooptask.

Havingsaidthis,integratingthebehavioraldatainto adiffusionde- cisionmodel,e.g.seeRatcliff andMcKoon(2008),couldbeusefulto bettercharacterizetheneuralandcognitiveprocessesofdecisionmak- ingintheface-wordStrooptask(andincomparisontothecolor-word Strooptask),butthisisbeyondthescopeofthecurrentstudy.Here,we focusedonhowmemoryprocessesweremodulatedbypreviouscon- flictprocessing.TheprecisemechanismsunderlyingtheStroopeffect indifferentparadigmsmaybeaddressedinfuturestudies.Moreover, RTandaccuracyassesspartlydifferent aspectsof conflictprocessing

andthe datado not suggestthat participantshavetraded speedfor accuracy.

Furthermore, none of the conflict-related activation clusters we found in the whole-brainanalysis in healthy controls turned out to be predictiveof healthysubjects’memoryperformance,neitherover bothtaskconditions,norspecificallyforfacesofincongruenttrials.This mightbeexplainedbyaninsufficientstudypower.Moreover,itmight berelatedtothegenerallyincreasedretrievalratesinhealthysubjectsin thepresentstudycomparedtothepreviousone(Krebsetal.,2015).To accountformemorydeficitsinMTLEpatients,weextendedthelearning phase(familiarization),assumingthatthismayreducememoryencod- ingdemandsduringtheactualStrooptask.Furthermore,theabsenceof neutraltrials(comparedtotheparadigminourpreviousstudy)possi- blyreducedthesaliencyoftheconflictcondition.Thus,wesuspectthat changes intheparadigmthatwerenecessaryforinvestigatingMTLE patientsreducedtheeffectsofcongruencyonmemoryandthecorre- spondingBOLDcontrastsof healthysubjects.Relatedtothis,thebe- havioralcongruencyeffectwasparticularlyevidentforthetrueremem- beredvs.forgottencomparison.However,whichtypeofmemory(i.e.

hippocampus-dependentepisodicdetailsorhippocampus-independent schematicinformation)isparticularlymodulatedbyconflict,cannotbe answeredbythecurrentstudy.Thismightbeaninterestingsteptowards abetterunderstandingofconflict-modulationofmemoryprocesses.Fur- thermore,incontrasttothebehavioralcontrast,thefMRIrecollection contrast (highconfidentvs.nothighconfidentrecollection)revealed morereliableeffectsduetobalanceditemnumbers.Thus,therelation betweenbehavioralandfMRIresultsislimited.

AnotherlimitationisthatpatientswithunilateralleftandrightMTLE aswellasbilateralMTLEwereinvolvedinthestudy,sothatwecannot inferwhetherthefMRIresultsaremodulatedbyepilepsylateralization.

WedidnotfurtheranalyzefMRIresultsofsubgroupsduetotheirsmall sample sizes.Thedelaybetweenlearningandretrievaltask wasnot identicalbetweensubjectsbutwasbetween30and45min.However, thedelayrandomlyvariedinallparticipantsanditisunlikelythata systematicerroraﬀectedgroupdiﬀerences.

5. Conclusion

Ourstudyprovidesfirstevidencethatthememorybenefitofcon- flictinginformationisabsentinMTLEpatientsandthusseemstocriti- callyrelyontheintegrityofthehippocampus.Inhealthyparticipants, thetwofunctionsofmemoryformationandresponseconflictresolution competedforresourcesinthehippocampus.Inaddition,posteriormid- lineareassuchasprecuneusandPCCsupportedconflictresolution.In MTLEpatients,theseposteriormidlineareasshowedreducedconflict- related activationbutwererecruitedfor memoryformation instead.

Theseresultswouldbeinlinewithalarge-scalereorganizationofmem- orynetworksinepilepsypatients.Thesealterationsmayberelatedto memoryimpairmentsand/ordeﬁcitsintheemploymentofmemoriesfor cognitivecontrolfunctions.However,furtherstudiesinhippocampus- lesionedpatientsareneededtotesttheassociation betweenepisodic memorynetworksandcognitivecontrolmechanisms.

DeclarationofCompetingInterest Theauthorsdeclarenoconﬂictofinterest.

Creditauthorshipcontributionstatement

MarkusRamm:Investigation,Writing-originaldraft,Writing-review & editing.BenediktSundermann: Writing-review& editing.

CarlosAlexandreGomes:Methodology.GabrielMöddel: Investiga- tion. LisaLangenbruch: Investigation.MahboobehDehghanNayy- eri: Methodology. PeterYoung: Funding acquisition. BettinaPﬂei- derer:Writing-review&editing.RuthM.Krebs:Conceptualization, Supervision,Fundingacquisition,Writing-review&editing.Nikolai