Motor cortex excitability is tightly coupled to observed movements

Althoughfacilitationofthecorticospinal(CS)systemduringactionobservationisawidelyaccepted phenomenon,itisstillcontroversialiffacilitationreflectsthereplicaofobservedmovementkinematics or thetensiontoachieveaparticulargoal.Inthisstudy,transcranialmagneticstimulation(TMS)- inducedmotorevokedpotentials(MEPs)wererecordedfromtheabductordigitiminimi(ADM)andthe first dorsalinterosseus(FDI)muscleswhileparticipant–volunteersobservedamodelgraspingasmall target elicitingaprecisiongriporalargetargetelicitingawholehandgraspdirectedtowardanisolated object orflankedbydifferentsizedobjects(i.e.,distractor).Adetailedmovementanalysisrevealedthat the model’skinematicswereinfluencedbythedistractor’ssize.Videoclipsfilmingthescenewere edited insuchawaythatthedistractorwasremovedfromthescene.Participant–volunteerswere asked toobserveactionscharacterizedbythesamegoalbutperformedusingdifferentkinematical patterns.Althoughthedifferencesinmovementkinematicswerenotnoticedbytheparticipant- volunteers,theynonethelesseliciteddistinctconfigurationsofcorticospinalactivation.Detailedmotor matchingseemstorecruitthesamemusclesintheonlookerasinthepersonactuallycarryingoutthe action duringobservationofgraspingactions.Theseeffectsappeartobeelicitedbyverysubtle, imperceptibleaspectsofobservedactionspointingtoafinelytunedmechanismthatspecifically encodesbodyparts.