reorganization of movement representations

J~URNALOFNEUROPHYSIOLOGY RAPIDPUBLICATION Vol.75,No.5,May1996.PrintedinU.S.A. ReorganizationofMovementRepresentationsinPrimaryMotorCortex FollowingFocalIschemicInfarctsinAdultSquirrelMonkeys RANDOLPHJ.NUDOANDGARRETTW.MILLIMEN DepartmentofiVeurohiologyand Anatomy,UniversityofTexas HealthScience CenteratHouston, Houston,Texas 77030 SUMMARYAND CONCLUSIONS 1.Intracorticalmicrostimulation(ICMS)techniqueswereused toderivedetailedmapsofdistalforelimbmovementrepresenta- tionsinprimarymotorcortex(area4)ofadultsquirrelmonkeys beforeandafewmonthsafterafocalischemicinfarct. 2.Infarctscausedamarkedbuttransientdeficitinuseofthe contralateralhand,asevidencedbyincreaseduseoftheipsilat- era1hand,andreducedperformanceonataskrequiringskilled digituse. 3.Infarctsresultedinawidespreadreductioninthearea1extent ofdigitrepresentationsadjacenttothelesion,andapparentin- creasesinadjacentproximalrepresentations. 4.Weconcludethatsubstantialfunctionalreorganizationoccurs inprimarymotorcortexofadultprimatesfollowingafocalisch- emitinfarct,butatleastintheabsenceofpostinfarcttraining, themovementsformerlyrepresentedintheinfarctedzonedonot reappearinadjacentcorticalregions. INTRODUCTION Despite overa centuryofstudy,the precise neurophysio- logicaland neuroanatomic mechanismsforfunctionalmotor recoveryaftercorticalinjuryarepoorlyunderstood(e.g., Bach-y-Rita1980).Earlystudies whichemployedsurface stimulationtechniques suggested thatthehandrepresenta- tioninprimarymotorcortexofadultprimatesundergoes substantial reorganizationfollowingsmall lesions, and that corticalreorganizationis correlated withfunctionalrecovery (GleesandCole1950).Thesestudies havenotbeenre- peated since theintroductionofintracorticalmicrostimula- tion(ICMS)techniques. Toexaminelesion-inducedplasticityinprimarymotor cortex(area4)inmoredetail,wehaveemployedICMS techniques toderivedetailed maps ofdistal forelimbrepre- sentations beforeanda fewmonthsaftera focalischemic infarct.Insharp contrasttoresultsobtainedbyGlees and Cole( 1950),movements represented intheinfarctedzone did not reappear in the corticalsector surrounding the infarct. METHODS StandardICMSmappingtechniqueswereemployedinninenor- mal,adultsquirrelmonkeys(Saimiriboliviensis)toderivemaps ofdistalforelimbrepresentations.Afterthederivationofbaseline maps,onegroupofanimalsunderwentischemicinfarctprocedures (~2 =5).Asecondgroupofanimals,servingas controls,underwent ICMSprocedures,butnoinfarct(n=4). Surgicalandelectrophysiologicaltechniques Understerileconditionsandafterinductionofhalothane/nitrous oxideanesthesia,area4contralateraltotheanimalspreferredhand wasexposed.Then,underketamineanesthesia( 15mgl kg-Il h -) , standardICMSmappingprocedureswereconducted(e.g.,Gouldet al.1986;Nudoetal.1992;StrickandPreston1982).Briefly,an electrolyte-filledglassmicropipettewasadvancedperpendicularto thecorticalsurfacetoa depthof1,700-1,800pmatseveralhundred siteswithinthedistalforelimb(digit,wrist,forearm)representation. Interpenetrationdistanceswere-250pmthroughoutthedistalfore- limbzone,and500-1,000pminthesurrounding,proximalzone. TheICMStrainburstconsistedof13200~pscathodalpulsesdeliv- eredat350Hzfromanelectricallyisolatedstimulationcircuit.Site- specificmovementsevokedat thresholdandata fixedsuprathreshold level(20PA)wererecorded(maximum=30PA).Withtheuse ofacomputeralgorithm,representationalmapsweredrawnbyout- liningcorticalsectorswhosestimulationevokedspecificmovements (seeNudoetal.1992forfurtherdetails). Aftermappingwascompleted,theanestheticregimenwas switchedtohalothane/nitrousoxide(infarctgroup).Smallcortical lesionsweremadebyusingmicroforcepsconnectedtoabipolar electrocoagulator.Bloodvesselswerepermanentlyoccludedas theyenteredthecorticalsurface.Theboundarybetweentheadja- cent,intactcortexwaseasilydiscerniblewithinafewminutes becausetheinfarctedtissuebecameblanchedthroughoutitsextent, whiletheadjacenttissueanditsvascularsupplyremainedintact. Theextentofthedamagedcortexwasthenmeasureddirectlyfrom comparisonofdigitalphotographstakenbeforeandseveralminutes aftertheinfarct.Thisboundarywaslaterverifiedbyexamining thefollowing:1)digitalphotographstakenimmediatelybeforethe postinfarctmappingprocedure,2)regionsunresponsivetoICMS inpostinfarctmaps,and3)postmortemhistologicalassessment. Theseproceduresverifiedthatimmediatepostinfarctestimatesof lesionsizewerereliable. ICMSprocedureswererepeated3 -5moaftertheischemicin- farct.Aftercompletionoftheseexperiments,eachanimalwas injectedwithalethaldoseofpentobarbital,perfusedwithfixative, andthebrainremovedforhistologicalexamination.Thearea3a/ 4borderwasdefined,andextentofthelesionverified. TheseproceduresareinaccordancewithNationalInstitutesof Healthguidelinesandwereapprovedbytheinstitutionalanimal careandusecommittee. Behavioraltechniques Toassessspontaneousreorganizationinmotormaps,nospecific behavioraltrainingprocedureswereemployedeitherbeforeor aftertheinfarct.Althoughextensivebehavioraltestingcouldhave introducedtrainingeffects,limitedtestingofmotorperformance wasconductedintwomonkeysbeforeandaftertheinfarct,to determinetheextentofthemotordeficitandtrackrecovery.Test- 21440022-3077/96$5.00Copyright01996TheAmericanPhysiologicalSociety REORGANIZATIONINMOTORCORTEX2145 A O-e-- CASE#I300 I - I - I - I -20 40 60 80 A14 MOTORMAP DAYSPOST-INFARCTMoTofRMAP &INFARCT C W0z-O z05 0.8- i ne 0.6- 5)-00.4- E o-2-- 4well1 ---I)-well4 MOTORMAP DAYSPOST-INFARCTMOTORMAP &INFARCT D f z a 0 IL 3 e u 0 I- O L CASE#I449 4 well1 I - I - I - I20 40 60 80 +--12 I c MOTORMAP DAYSPOST-INFARCTMOTOR,c,, &INFARCT n4well1 +well4 -.- -200 20 40 60 80 -1204DAYSPOST-INFARCT MOTORMAP MOTORiAp &INFARCT FIG.1.Effectsofischemicinfarctonlateralityandmotorperformance.AandB:percentretrievalswiththehand contralateraltotheinfarctareshownforeachwell.A:lateralitywasnormalforeachwellby60days.Monkeypersistedin usingthecontralateralhandonwell4trialsthroughouttherecoveryperiod.B:lateralitywasnormalforwellsl-3by40 days.CandD:motorperformanceonbothwellswasnearnormallevelsbyday60inCandbyday40inD.Motor performanceisdefinedas(totalnumberfingerflexions/totalnumberretrievals)-I.Maximalperformance=1.0.Forclarity, motorperformanceonlyonwells1(25mmdiam)and4(9.5-mmdiam)areshown. ingwasconductedbyusingaPlexiglasboardcontainingfood wellsofdifferentdiameters(Nudoetal.1992).Afoodpelletwas pairedhand,theyrequiredmorefingerflexionsperre- placedrandomlyintooneofthewells,andtheanimalwasallowed trieval,especiallyonthesmallest well(Fig.3,Cand 0). toretrieveitwiththedigitsofeitherhand.Tentrialsperwell Thisdeficitwas marked inthe firsttwowkafterthe lesion, wereconductedoneachtestingdayandvideotaped.Byanalyzing butwithin2 mo,motorperformancereturnedto preopera- thevideotapesframe-byframe,wenotedforeachtrialthetotal tivelevels.Videotapesofnormalcagebehaviorofthe numberoffingerflexionsandthehandusedtoretrievethepellet threeothermonkeysindicatednodiscernibledeficitsin successfullv. climbingorfeedingwiththecontralateralhand beforethe J finalmappingprocedure. RESULTS Eflectsof focalischemic infarctsonmotorbehavior Eflectsoffocalischemic infarctson adjacentmovement representations LimitedtestingontheKliiverboardintwomonkeys indicatedthatthe infarctresulted indeficitsinskilleduse ofthecontralateralhand(Fig.1).Duringthepostinfarct period,monkeysgenerallyused the contralateralhand less thantheydidbeforetheinfarcttoretrievepellets.How- ever,one monkeypersisted inuse ofthe contralateralhand onthesmallest well(Fig.1A).Althoughmonkeyswere able toretrievefoodpelletsfromeach wellwiththeim- Baseline maps ofmovementrepresentations were similar tothose previouslyreported(e.g.,Gouldetal.1986; Nudo etal.1992;Fig.2C).Thedistalforelimbrepresentation (digit,wrist/forearm)wascontiguousandbounded medi- ally,rostrally,and laterallybyproximalmovement represen- tations(elbowandshoulder),andcaudallybyalargely nonresponsive zone(area3a).Responsive sites inarea 3a wereeliminatedfromstatisticalanalysis. 2146R.J.NUDOANDG.W.MILLIKEN APRE-INFARCT B 3MONTHSPOST-INFARCT ,A#area 250pm area4,A ,,.AGrea3a DISTALDIGITWRIST/ FORELIMBFOREARM FIG.2.Remodelingofmotorrepresentationsinarea4followingafocalischemicinfarct,AandB:photographsofcortical vasculature.Cand19:Intracorticalmicrostimulation(TCMS)-derivedmapsofdistalforelimbmovements.Infarctdestroyed 21%ofdigitand7%ofwrist/forearmrepresentationwithinarea4.Whitedotsindicatemicroelectrodcpenetrations.Area 3a/4borderindicatedbygraydiagonalline,E:arealchangesinmovementrepresentationsurroundinginfarct.Undamaged digitareaadjacenttothelesiondecreasedby40%.L:cresylviolet-stainedcoronalsectionthroughtheinfarctedzone.False sulcus(i);zoneoflowneuronaldensityandhighgliadensityboundedby(...).Scalebar=Imm.Distalforelimb consistsofdigitandwrist/forearm.Proximalconsistsofelbowandshoulder. REORGANIZATIONINMOTORCORTEX2147 CONTROLSPONTANEOUS RECOVERY ndistalforelimb 0 wrist/forearm FIG. 3.Changeindistalforelimbrepresentationsincontrolgroup(n= 4)andspontaneousrecoverygroup(n=4).(*),statisticallysignificant differencesbetweenpre-andpostinfarctmapsbyusingposthocpairedt- tests(P