Transcranial magnetic stimulation and preparation of visually-guided reaching movements

Tobetterdefinetheneuralnetworksrelatedtopreparationofreaching,weappliedtranscranialmagneticstimulation(TMS)tothelateralparietalandfrontalcortex.TMSdidnotevokeeffectscloselyrelatedtopreparationofreaching,suggestingthatneuralnetworksalreadyidentifiedbyourgrouparenotlargerthanpreviouslythought.WealsoreplicatedpreviousTMS/EEGdatabyapplyingTMStotheparietalcortex:newanalyseswereperformedtobettersupportreliabilityofalreadyreportedfindings(Zanonetal.,2010;BrainTopography22,307–317).Weshowedtheexistenceofneuralcircuitsrangingfromposteriortofrontalregionsofthebrainafterthestimulationofparietalcortex,supportingtheideaofstrongconnectionsamongtheseareasandsuggestingtheirpossibletemporaldynamic.Connectionwithventralstreamwasconfirmed.Thepresentworkhelpstodefinethoseareaswhichareinvolvedinpreparationofnaturalreachinginhumans.Theycorrespondtoparieto-occipital,parietalandpremotormedialregionsofthelefthemisphere,i.e.,thecontralateralonewithrespecttothemovinghand,assuggestedbypreviousstudies.Behavioraldatasupporttheexistenceofadiscretestreaminvolvedinreaching.Besidestheserialflowofactivationfromposteriortoanteriordirection,aparallelelaborationofinformationamongparietalandpremotorareasseemsalsotoexist.Presentcortico-corticalinteractions(TMS/EEGexperiment)showpropagationofactivitytofrontal,temporal,parietalandmoreposteriorregions,exhibitingdistributedcommunicationamongvariousareasinthebrain.TheneuralsystemhighlightedbyTMS/EEGexperimentsiswiderwithrespecttotheonedisclosedbytheTMSbehavioralapproach.Furtherstudiesareneededtounravelthispaucityofoverlap.Moreover,theunderstandingofthesemechanismsiscrucialforthecomprehensionofresponseinhibitionandchangesinpreparedactions,whicharecommonbehaviorsineverydaylife.