march 10, 2016 - 國立交通大學開放式課程...

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Chapter4TheImagedBrain

March10,2016

5707BrainandCognitiveScience

MethodsforBrainandCognitiveScience

Electrophysiology:Electroencephalography(EEG)Magnetoencephalography (MEG)Transcranial magneticstimulation(TMS)

Neuroimaging:MagneticResonanceImaging(MRI)functionalMRI(fMRI)Positronemissiontomography(PET)

Chapter3ElectrophysiologicalBrain

Chapter4ImagedBrain

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PaulBroca (1824 1880):Tansbrain

Apatient,withlossofspeechwastransferredtoPaulBrocas care LosttheabilitytospeakexceptforTan. Goodcomprehension Braindamagetothelefthemisphere.

CarlWernicke (1848 1904)

Reported acaseofawomanwithdisruptedbutfluentspeech (1874)Fluentbutmeaningless speechComprehension isimpairedBraindamagetothelefthemisphere

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Leftsideofthebrain

Arcuatefasciculus:connectionbetweenBrocas areaandWernickesarea

Outlinefortoday

Thebasicconceptofimages Structural/anatomicalbrainimagingtechniquesCT/structuralMRI/DiffusionMRIPrincipleApplications

Functionalbrainimagingtechniques TaskrelatedfunctionalMRI(taskfMRI)PrincipleExperimentaldesignApplications

RestingstatefunctionalMRI(rsfMRI)andgraphtheory

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Thebasicconceptofimages

Beforeanyimageprocessing,weneedtounderstandtheformatoftheimage.

Neuralimagesaredigitalimages.

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Resolutionofanimage

lowresolution highresolution


Whatistheformatoftheimage? digitalimages

Adigitalimage=Amatrixofnumbers,w/onenumberrepresentsonepixel

Pixel =Pictureelement Adigitalimage=Amathematicalmatrix

222 220 200 146 103

200 158 127 96 73

207 131 103 82 86

202 126 112 124 133

PixelValues(p)

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Columns(j)

Rows(i)

Pixel Datap(i,j)


PixelsandImageMatrices numbersofpixels=numberofrows* numberofcolumns

Frommathematicstophysics

Adigitalimage=amathematicalmatrix Apixelinthematrixhasaphysicaldimension(e.g.mm)

1024x1024 64x64 32x32 16x16

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Frommathematicstophysics

Adigitalimage=amathematicalmatrix Apixelinthematrixhasaphysicaldimension(e.g.mm)

8mm 4mm 2mm 1.5mm 1mm

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Computedtomography(CT)

ProjectionoftheXrayfrommultipleangles 3Dimagesbasedontissuedensity

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Necessaryequipment:3TeslaMRIscanner

Magnet

Gradientcoil

RFcoil

http://www.magnet.fsu.edu/education/tutorials/magnetacademy/mri/fullarticle.html

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WhatdoesanMRIscansoundlike

HighresolutionT1structuralMRIimages

graymatter(morewater)

whitematter(morefat)

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3TMRIscandemohttps://www.youtube.com/watch?v=Gs3onhjuKio

Magnet

Earthsmagneticfield=0.5Gauss

1Tesla=10,000Gauss 3Tesla(T)=

3X10,000/0.5=60,000Earthsmagneticfield

Permanent Superconducting Activeshielding

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Review:Magneticfield

GradientCoil

Gradientstrength Activeshielding Shimming

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Radiofrequency(RF)coil

Transmission Receiving Severalkindsofcoils:

ActivecoilsPassivecoilsBirdcagecoils

MRIsafety

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MRIsafetyvideoIhttp://www.youtube.com/watch?v=6BBx8BwLhqg&feature=related

MRIsafetyvideoII

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https://www.youtube.com/watch?v=5KuzTyn45og

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Subjectsafety

Anyonegoingnearthemagnet subjects,staffandvisitors mustbethoroughlyscreened

Subjectsmusthavenometalintheirbodies:pacemaker aneurysmclipsmetalimplants(e.g.,cochlearimplants) somedentalwork(fillingsokay)

Subjectsmustremovemetalfromtheirbodies jewellery,watch,piercings,coins,etc.wallet anymetalthatmaydistortthefield

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fmri

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MagneticResonanceImaging(MRI)

MRI=NMR+Imaging Magnetic:Magnetizationinducedbymagneticfield

Resonance:Exciteandreceiveofmagnetization

Imaging:Spatialencodingofmagnetization()

MRImeasures

Differenttissueinthebrain(e.g.,graymatter,whitematter)

Differenttissuehasdifferentwatercontent Watercontainshydrogenatoms(H20)

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Magnetizationinducedbymagneticfield

+ =()(spin)

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MRIsignalvariesacrosstissue

Time

Signalintensity

TissueA(e.g.,fat)

TissueB(e.g.,water)

HighresolutionT1structuralMRIimages

graymatter(morewater)

whitematter(morefat)

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Structuralimaging

CT T1MRIimage T2MRIimage

Howtomeasurethedifferencesbetweengroups?

Normalyoungadult(mid20s)

Normalolderadult(late70s)

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Voxelbasedmorphometry analysis(VBM)

voxelwisecomparisonofthelocalvolumeofgraymatterandwhitematterbetweentwogroupsofsubjects

StructuralMRI:Voxelbasedmorphometry analysis(VBM)

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StructuralMRIapplication:IQandcorticaldevelopment

StructuralMRIapplication:IQandcorticaldevelopment

Moreintelligentchildrendemonstrateaparticularlyplasticcortex,withaninitialacceleratedandprolongedphaseofcorticalincrease:theneuroanatomicalexpressionofintelligenceinchildrenisdynamic

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StructuralMRIapplication:Learningandmemory

Changesingraymatterinducedbytraining: StudentsinexperienceatjugglingDividedintotwogroups(scanthem)Onegroupspracticesjugglingfor3months,andtheotherdoesnt(scanagain)

Wait3months,noonejuggles(scanagain)

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LargerposteriorhippocampusinLondontaxidrivers:LondontaxidriverisbetteronspatialnavigationOver26,000streetswithinasixmileradiusofCharing Crossand1,400differentplacesofinterests.

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LargerposteriorhippocampusinLondontaxidrivers: StructureMRIscan:16licensedLondontaxidriversand50nontaxidrivers.

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Restricteddiffusion:AnisotropicdiffusionFractionalAnisotrophy (FA)~1

Freediffusion:IsotropicdiffusionFractionalAnisotrophy (FA)~0

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DiffusionMRI:Diffusiontensorimaging(DTI)

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NeuralfiberreconstructionCalculationofthediffusiontensor

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DiffusionMRI:Diffusiontensorimaging(DTI)

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DTIapplications:sexdifferences

Malebrain Femalebrain

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DTIapplicationsEvolutionofthearcuatefasciculus

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10invivohuman1invivochimpanzee3postmortemchimpanzee1invivomacaque2postmortemmacaque

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MRIvs.fMRI

MRI studiesbrainanatomy Functional MRI(fMRI)studiesbrainfunction

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MRIscannerandfMRIscan

ThefirstBrainImagingexperiment

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Vasculatureofhumanbrain

Cerebralmetabolism:neuronalenergyconsumption

fMRIindirectlymeasurebrainfunction

Functionalbrainmaps:mapsofneuralactivity Mapsofneuralactivity:

Imagingthechangeinbloodflow(hemodynamicresponse)relatedtoenergyusebyneurons.

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Oxygenated BloodDeoxygenated Blood

Resting

Active

fMRI:BOLDsignal

BloodOxygenationLevelDependent(BOLD)signal

MRI

Neural

Metabolic

Hemodynamic

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CategoriesoffunctionalMRI

TaskrelatedfMRISpecificexperimentaldesigntoexaminethebrainfunctionsassociatedwithperception,attention,language,learningandmemory,decisionmaking,andemotion.Brainduringwork

RestingstatefMRINospecificexperimentaldesign Brainatrest




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taskrelatedfMRI(taskfMRI):Physicaltask

+

1000ms500ms 4 9

+

1000ms500ms 3 3

+Time

...1000ms500ms 2 7

TaskfMRIDatatransformations

Motioncorrection Smoothing

kernel

Spatialnormalization

Standardtemplate

fMRItimeseries

GeneralLinearModel

Designmatrix

Parameterestimates

Gaussianfieldtheory

p

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TaskfMRIresults

TasksfMRIbasic:orientation

Sliceorientation:AP:anteriorposterior()SI:superiorinferior()LR:leftright()

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TaskfMRIbasic:orientation

NeurologicalconventionLeftisleft,rightisright

Radiologicalconvention Leftisright,rightisleft

Makesurehowyoursoftwaredoingwithleft/right Ifyourereallyunsure,tapeavitaminEoroilcapsuletotheonesideofthesubjectshead.Itwillshowupontheanatomicalimage

left

left

right

right

IntroductiontotaskfMRIhttps://www.youtube.com/watch?v=BmQR57V5TVU

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Experimentaldesigns

BetweensubjectdesignDifferentconditionsareassignedtodifferentsubjectgroupse.g.malevs.female;drugabuservs.abstainers;youngvs.olderadults.

WithinsubjectdesignEachsubjectparticipantsinallexperimentalconditions

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Essentialcomponentsinanexperimentaldesign

IndependentvariablesManipulatedbytheexperimenterse.g.stimulus(face,words,pictures)

DependentvariableQuantitiesthatmeasuredbyexperimenters

e.g.,heartrate,bloodpressure,cortisollevel,BOLDsignal

e.g.,accuracy,reactiontimes

Variables:

Anterior

PosteriorLOCLOC

Experimentaldesigns Experimentalconditions Containsthestimuliortask

thatismostrelevanttoresearchhypothesis

Taskcondition

Controlconditions Baselinecondition Nontask condition

Experimentalcondition

Controlcondition

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Experimentaldesigns:fMRI

Experimentalconditions Controlconditions

faces Scrambledpicturesw/samespatialfrequency

=

TaskfMRIstudies:theoreticallydriven

Welldefinedproblem

TheoryA PredictionATheoryB PredictionB

Experiment

TheoryAorBstandsorrevisedtheory

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TaskfMRIstudies:theoreticallydriven

Anterior

PosteriorLOCLOC

Differentstimuluscategorieselicitdifferentpatternsofactivityinventralvisualcortex.

Predictions: Facerecognitiontaskleadtoactivationinfusiformfacearea Animacy judgmenttaskleadtoactivationinlateraloccipitalcomplex

Place/HouseAreas(Parahippocampal gyrus)

ObjectAreas(Lateraloccipitalcomplex)

FaceAreas(FusiformFaceArea)

ThreedistinctlevelsofresearchhypothesisintaskfMRIstudies

Hemodynamic

Neuronal

Psychological(Cognitive)

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Confoundingfactors

Anypropertythatcovarieswiththeindependentvariablewithintheconductedexperiment

Couldbedistinguishedfromtheindependentvariablesusingadifferentexperimentaldesign

ExampleofconfoundingCleverHans

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CleverHanseffect:Observerexpectancy

WhenHansisclever WhenHansisnotclever

Confoundingfactors

Anypropertythatcovarieswiththeindependentvariablewithintheconductedexperiment

Couldbedistinguishedfromtheindependentvariablesusingadifferentexperimentaldesign

Evidenceofglobalwarming?

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Topreventconfoundingfactors

Randomizing orCounterbalancingtheorderoftheconditionsmakessurethatthepotentialeffectsaredistributedequallyacrosstheconditionsoftheexperiment. Randomized:ABC,ACB,BCA,BAC,CAB,CBA(N!)

4conditions:24;5conditions:120;6conditions:720

Counterbalancing:ABC,BCA,CABEaseofusage:donthavetoswitchinstructionsorequipmentveryoften

TaskfMRIapplication:Decodingthereadingbrain

Hearingwords:Superior/middletemporalregions

Seeingwords:Leftoccipitotemporalregion

Petersenetal.,1988

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Speaking/producingwords:Motorregion

Generatingwords:Leftinferiorfrontalregion

TaskfMRIapplication:DecodingthereadingbrainPetersenetal.,1988

TaskfMRIapplication:ColorwordStrooptask

Congruent()

Incongruent()

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TaskfMRIapplication:consciousness?

Awarenessinthevegetativestate 23yearoldwomansustainedaseveretraumaticbraininjury Spokeninstructionstoperformtwomentalimagerytasks: imagingplayingagameoftennis imagingvisitingalloftheromofherhouse

Advantages&disadvantagesoffMRI

AdvantagesNoninvasiveSpatialresolutionisgoodShowsallparticipatingareas,notjustcriticalones

DisadvantagesPoortemporalresolutionDifficulttousewithsubjectsandtoobtaingoodmeasurementsSensitivitytoheadmotionPregnancy,obesity,metalparts,etc.

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Aneuralportraitofthehumanmind

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http://is.gd/cpNjvA

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Restingstatebrainactivity

RestingstatebrainactivityassessedbyfMRINoninvasive,bloodoxygenleveldependent(BOLD)

Defaultmodenetwork(DMN):AsetofbrainregionsshowingincreasedfMRIactivityintaskfreestatecomparedtocognitivelydemandingtaskatrest.deactivationSuperior/middlefrontal,medialprefrontal,posteriorcingulatecortex(PCC)/precuneus,superiorparietal,hippocampalregion.

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Defaultmodenetwork(DMN)&Taskrelatedactivationregions

Parketal.,2010

Young

rsfMRIapplication:mindwandering

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rsfMRIapplication:mindwandering

CorrelationbetweenmindwanderingfrequencyandBOLDchange

Smallworld:Graphtheory

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Smallworld:Graphtheory

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WhatisrestingstatefMRI?

96Adaptedfrom,2015

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Functionalneuralconnectivity:restingstatefunctionalMRI

Stronglycorrelatedpatternsofbrainactivityamongdistantbrainregions(i.e.,functionalconnectivity)aretakenasanindicationthattheseregionscommunicate.

Functionalconnectivityisoftenmeasuredasinterregionalcorrelationsamongspontaneousfluctuationsofhemodynamicactivityduringarestingstate whileparticipantsliepassivelyintheMRImachine,butnoactivecognitiveorbehavioraldemandsareimposed.

Dosenbach etal.,2008

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march 10, 2016 - 國立交通大學開放式課程...

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