The Components of Imitation

TheComponentsofImitation
Onefunctionthatinvolvesstructuresintwocerebralhemispheres
December22,2015
Welearnmanythingsthroughimitation:howtowalk,playaninstument,sports,andevenmore.
Whataretheprocessesinthebrainresponsibleforimitation?Forsomeyearsnow,sciencehas
beenexaminingtheroleofmirrorneurons,butthereisstillmuchtounderstand.Onestudy
focusingonneurologicalpatientsshowedthatatleasttwocomponentsareinvolvedinimitating
gestures,eachfromadifferenthemisphereofthebrain.Thestudy,whichSISSAparticipatedin,
waspublishedinNeuropsychologia
Afterabraininjury(causedbystrokeorhemorrhage,forexample),patientsmayhavedifficulty
imitatinggesturesandmovementsofothers(ideomotorapraxia).Inthehistoryof
neuropsychology,thesestudiesareamongthebestknown(thefirstdatebacktotheearly1900’s)
asthesedeficitshindertherapyaimedatrecoveringmotorskills,sincethepatientcannot
performgesturesbyimitatingthedoctor.Inthelasttwentyyears,thesestudieshavefoundnew
significancethankstothediscoveryofmirrorneurons,andyetlittleisknownaboutthese
processes.Manyscientiststhinkthelefthemisphereplaysadominantrolebecausethisproblem
mostoftensurfacesincasesofunilateralbrain-damageofthelefthemisphere.Howthen,canwe
explainthesmallpercentageofapraxicpatientswhohavesufferedunilaterallesionstotheright
hemisphere?
PaolaMengotti,atSISSAatthetimeofthestudy,nowatForschungszentrumJülichinGermany,
SISSAProfessorandHeadoftheiNSuLaLaboratory(NeuroscienceandSociety),Raffaella
Rumiati,andcolleaguesconductedastudytoanswerthisquestion.Twentypatients(visitedat
SanCamilloinVeniceandAziendaOspedaliero-UniversitariaOspedaliRiunitiinTrieste)with
unilateralbrainlesionsintheleftorrighthemispheres,plusacontrolgroupparticipatedinthe
study.Theinitialideawasthatimitationismadeupofatleasttwodistincttasks:motorimitation,
andaspatialcomponent.Whenwehavetoimitatesomeoneelse’smovements,wenotonlyhave
torepeattheactions,butwealsohavetotranslatethemtoourbody(mirrorthem).Inthestudy,
patientsperformedimitationtasksusingoneofthetwocomponents,motororspatial.
Performanceforeachcomponentwasthencomparedandcategorizedinrelationtothetypeof
lesion.
Whatemergedisthatwhatcountsinimitationisthesimilaritybetweenwhatisseenandwhatis
produced,andthisofcoursedependsontheindividualtypeofdeficit."Analyzingthe
performanceoftwoimitationtasksbypatientswithlesionsintherighthemisphereandtheleft
hemisphere,wewereabletodemonstratethatimitationisbasedonthesimilaritybetweenthe
observedactionandtheoneproduced,"explainsRumiati."Thissimilarityreflectseitheran
anatomicalmatchoraspatialone.Lesionsinthelefthemisphereaffecttheformerwhilelesions
intherighthemisphereaffectthelatter."
USEFULLINKS:
• OriginalpaperonNeuropsychologia:http://goo.gl/DjV6QG
IMAGE:
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Credits:JamieMcCaffrey(Flickr:https://goo.gl/5XffDR)
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