The Brain Damage That Hides Half the World - The Atlantic

Hemispatial neglect is the purest known disruption of consciousness caused by brain damage. You can process information on the bad side and ... SkiptocontentSiteNavigationTheAtlanticPopularLatestSectionsPoliticsIdeasFictionTechnologySciencePhotoBusinessCulturePlanetGlobalBooksPodcastsHealthEducationProjectsAmericaInPersonFamilyEventsShadowlandInheritanceNewslettersTheAtlanticCrosswordPlayCrosswordThePrintEditionLatestIssuePastIssuesGiveaGiftSearchTheAtlanticQuickLinksDearTherapistCrosswordPuzzleManageSubscriptionPopularLatestSignInSubscribeOnlythroughNovember30:TrysubscribernewslettersforfreeWhenIwasagraduatestudent25yearsago,ImetamanI’llcallMr.X,whohadrecentlyrecoveredfromastroketotherightsideofhiscerebralcortex.Likemanypeoplewithaneurologicaldisability,hewasintenselycuriousabouthiscondition,andonhisowninitiativehevisitedtheneurosciencelabwhereIworked.Hewasafriendly,engaged,intelligentmanofabout60.Hewasn’tallowedtodrive,buthehadnoobvioustroublewalking,speaking,orinteractingwithpeople.Icouldn’tseeanylingeringsymptomsinacasualconversation.Heshookhandsfirmly.Hecouldtakecareofhimself.Withhispermission,useagergraduatestudentsputhimthroughastandardclinicalassessment.Thistypeofassessmentisdesignedtobefastandlow-techforeasyuseatahospitalbedside.Wetookalargesheetofpaper,filleditwithscatteredhorizontallinesegmentsaboutaninchlong,andputitonatableinfrontofhim.Thenwegavehimamarkerandaskedhimtoputaverticalmarkthrougheveryhorizontallineonthepage.Irememberhelaughedandsaid,“Thisagain!”beforeconfidentlycrossingouteveryhorizontallineontheright-handsideofthepage,butnoneontheleft.Itlookedalmostlikeajoke,butitwasn’t.Hemispatialneglectisthepurestknowndisruptionofconsciousnesscausedbybraindamage.Wepressedhimtotryagain—toscanthepageandmakesurehegoteverytarget.Afterstaringintently,hesaid,“Oops,”andcrossedoutanothertwolinesnearthemiddleofthepage.Hestillhadmissedeverylineontheleft.Then,ashewatched,werotatedthepageuntiltheleftwasontheright.Hegaveastart,andlaughedinastonishment.Wehaddoneamagictrick,asfarashewasconcerned.Suddenlyhewasawareofallthelineshehadmissed.Theywereonhisgoodsidenow.Hehadnoideawheretheyhadcomefrom,buthecouldfinallycrossthemout.Wewereprettysurehedidn’thaveaproblemwithhiseyes.Ifsomeoneisblindinapartofthevisualfield,theyknowtomovetheireyesandheadtoscanthewholeworld.Ifsomeonepressesyoutopointtoeveryobjectintheroom,youwouldremembertoturnaroundandpointtotheobjectsbehindyourheadeventhoughtheywereoriginallyoutofyourvision.ButMr.Xwasdifferent.Hesufferedfromasyndromecalledhemispatialneglect.Nomatterhowhardhewaspressedtotry,hehadnoconceptoftheleftsideofspace.IwishwehadtriedafewmoreexperimentsonMr.X.Themoreyoudigintotheneglectsyndrome,themoreyouseetheseamsinthemind.Inmanypatients,ifyougivethemthesamekindoftasksuchascancellinglinesonapage,butthelinesaredrawnonawallacoupleofyardsawayandthepatientisgivenalaserpointer,theneglectgoesaway.Thepatientcanprocessbothsidesofthewallperfectly,justnotonapieceofpaperinfrontofthem.Evenmorebizarre,ifyougivethesamepersonalongstickinsteadofalaserpointer,theneglectcomesback.Theytouchthedistanttargetsonthewallwiththestick,buttheyignorethetargetsontheleftsideofthewall.Laserpointer,noproblem.Stick,theleftsideofspacedisappears.Resultslikethisshowthatthebrainbreaksspaceintoatleasttwoparts:thespaceofthingsyoucanreachwithyourhandsorahand-heldtool,andthespacetoofarawaytoreach.Insomepatients,thereachingandtool-usingspaceisdamagedandtheneglectislimitedtoit.Inotherpatients,onlythedistant,unreachablespaceisaffected.Somepatientssufferboth.OurMr.Xprobablyhadaneglectlimitedtothenearspace,sincehewasabletonavigatequitewellwalkingaround.Oneofthemostbeautifulandrevealingexperimentsonneglectshowedthatitisnotjustabouttheworldaroundyou,whethernearordistant,butalsoabouttheworldinsideyourimagination.Thestudyinvolvedpatientswhosefarspacewasaffected.Ifyouaskoneofthosepatientstoclosehiseyesandimaginestandingatthenorthendofafamiliarcitysquare,hecandescribethesquarefrommemory.Buthe’lllistonlythebuildingsonhisrightside,withoutnoticingthathe’sgivenanincompleteaccount.IfyouaskhimtoimaginestandingontheSouthendofthesamesquare,nowhe’llsuddenlyremembertheoppositesetofbuildings,ontherightsideofhisnewperspective,whileforgettingthefirstsetofbuildingsnowonhisleft.Thisexperimentdoesn’ttestlinesonapageoronawall,oranypartoftheworldactuallyinfrontofthepatient.Thewholetestliesinthepatient’smemoryandimagination.Hisbrainsimplycannolongerhandletheleftsideofspace.Ofcoursepatientsinthesesituationsoftennoticethatthey’vegivencontradictoryanswers.Itdistressesthem,buttheycan’tunderstandwhathasgonewrong.Theveryconceptoftheleftsideofspacehasbeenerased.Thenextpictureshowsthesamehouse,but...withflamesshootingoutofthewindowsontheleftsideEverythingI’vedescribedsofaraboutneglectinvolvesfailingtonoticeorreacttoobjectsontheneglectedside.Thoseobjectsareerasedfromconsciousness.Buttheyarenoterasedalltogether.Neglectismuchmoretwistedthanasimplementalblank.Itturnsoutthepatientdoesprocessinformationfromtheneglectedside,butdoesn’tknowit.Thathiddenprocessingwasrevealedinaparticularlypoignantwayinonestudy.Picturesareprojectedonascreeninfrontofaneglectpatient.Onepictureshowsahouse.Theneglectpatientcanseeit’sahouseandanswerquestionsaboutit,althoughheislikelytomissthewindowsorthebushesontheleftside.Ifaskedtodrawthehouse,he’llprobablydrawonlyhalfofit.Hesaysit’saverynicehouse,andhe’dbehappytoliveinit.Thenextpictureshowsthesamehouse,butthistimewithflamesshootingoutofthewindowsontheleftside.Again,thepatientknowsit’sahouse.Hecandescribeit,andasexpected,heneglectstomentiontheflames.He’sunawarethatthishouseisonfire.Butifyouaskhimabouthisemotionalreaction,he’llsaythathedoesn’tlikethehouse.There’ssomethingverywrongwithitandhewouldn’twanttolivethere.Thevisualinformationisgettingin.Brainimagingstudiesshowthatthevisualcortexisactivetothehighestlevels.Hecanprocessstuffontheleftside.Hejustcan’tattachthepropertyofconsciousnesstoit.Hemispatialneglectisthepurestknowndisruptionofconsciousnesscausedbybraindamage.Youcanprocessinformationonthebadsideandreacttoitinsubtleandevenverycomplexways,butyou’renotconsciousofit.Oneofthelessonsfromneglectisthat,despitethecommonintuition,consciousnessisnotasingle,unifiedentity.Itbreaksapartalongspatiallines—leftversusrightandnearversusfar.Damagetoalotofbrainareascancauseneglect,butthemostsevereandlonglastingcasesarecausedbydamagetoaspecificarea,oneofthemostwidelyconnectednodesinthebrain,thejunctionbetweenthetemporallobeandtheparietallobe—moreorlessjustaboveyourear.Thistemporoparietaljunction,orTPJ,isconnectedtosocialnetworks,cognitivecontrolnetworks,attentionnetworks,andmemorynetworks.It’sapoorlyunderstoodbutobviouslycrucialnexusofinformationinthebrain.