Brain Mapping and Functional Brain ImagingMethods of localizationIntra-operative MappingIntra-operative brain mappingElectrical stimulation mapping (A type of intra-operative mapping)George Ojemann and Neil’s Brain (electrical stimulation mapping)Probing Neil’s brain (Ojemann)“Naming sites” found in Neil’s brainProbing Neil’s brain – “Naming sites”“Naming sites” identified in the experiment“Naming sites” – English and SpanishTranscranial Magnetic Stimulation - TMSBrain imaging and functional brain imagingFunctional Brain Imaging TechniquesElectroencephalography (EEG)EEG MappingMultiple electrodes for mappingERP MappingEEG-MRI CoregistrationEEG-MRI Co-registrationSome Properties of EEG-ERP MappingDetecting electrical activityDipolesSource and volume currentsVolume CurrentsPositron Emission Tomography (PET) (1) tomography: pictures of slices tomo- ‘slice’ graph “picture’ (2) produced by a technique based on emission of positronsAxial sections: commonly used in brain imagingPET MachineIn a PET MachinePositron Emission Tomography (PET)Slide 31Slide 32Some PET ImagesMore PET ImagesSome properties of PETPET study of object categoriesCategories testedSubjects, method, and findingsPatients with defects in more than one catetoryDeficits vis-à-vis areas of damageSimilar results from PET experiment on normal subjectsFunctional Magnetic Resonance Imaging (fMRI)Slide 43Slide 44MRI MachineAnother MRI MachineSlide 47fMRI: ExampleAnother exampleSlide 50Active areaArea that “lights up” (hypothetical example)Slide 53Slide 54Brain Mappingand Functional Brain ImagingLing 411 – 09Methods of localizationLesion studies•The traditional method•For a long time, the only methodIntra-operative mapping•Started by Penfield and Roberts , 1960’sTranscranial magnetic stimulation (TMS)•Recently developed•Very promisingFunctional brain imaging•Currently very popular•Many techniquesIntra-operative MappingIntra-operative brain mappingPerformed on exposed neural tissue•After craniotomy•Used only in pathological conditionsE.g., epilepsyMethods in use•Electrical stimulation mapping •Electrocorticograms •Microelectrode recordingsElectrical stimulation mapping(A type of intra-operative mapping)Early work by Penfield and Roberts•Montreal More recently, George Ojemann – neurosurgeon, U. of Washington•Book: Conversations with Neil’s brain (with W. Calvin, 1994)•Neil, a patient, suffers from epilepsyCurrently, in Texas Medical Center•Nitin Tandon, UTGeorge Ojemann and Neil’s Brain(electrical stimulation mapping)George Ojemann – neurosurgeon, U. of Washington•Book: Conversations with Neil’s brain (with W. Calvin, 1994)•Neil, a patient, suffers from epilepsyIntraoperative probing of part of Neil’s brain•In the area suspected of causing seizures•Probing to spare vital linguistic functions•Additional probing for researchProbing Neil’s brain (Ojemann)Aim: to localize functionsArea activated – “size of pencil eraser”•I.e., about 1 sq cm•Number of neurons under 1 sq cm of cortical surface: 14,000,000Test for “naming sites”•Problem“Naming sites” found in Neil’s brainProbing Neil’s brain – “Naming sites”Problems with “naming sites”•Naming is a complex functionTherefore, not localizable•Ojemann doesn’t distinguish different kinds of objectsAdditional problem in interpreting results:•Input for testing is only pictures – visual stimuli•Same problem comes up with results of many imaging studies“Naming sites” identified in the experiment1. In Broca’s area2. In Wernicke’s area3. In supramarginal gyrus •N.B.: Angular gyrus not considered•Was not under the section of skull removed•Might also be involved (?)“Naming sites” – English and SpanishTranscranial Magnetic Stimulation - TMSMagnetic stimulation disrupts electrical activityTMS disrupts activity only while it is being applied•Recovery is immediateCan induce temporary dysfunction of specific areas – e.g. Broca’s areaUsefulness depends greatly on areal precision, a function of expenseBrain imaging and functional brain imagingBrain imaging•Gets static image•Used for example in locating lesion areas•E.g. MRIFunctional brain imaging•Images of brain performing more or less specific functionE.g., linguistic, motor, sensory, attentionThat is the ideal, never actually realized•E.g. fMRIFunctional Brain Imaging TechniquesElectroencephalography (EEG)Positron Emission Tomography (PET)Functional Magnetic Resonance Imaging (fMRI)Magnetoencephalography (MEG)•Magnetic source imaging (MSI)Combines MEG with MRIElectroencephalography (EEG)An old technique, from the days before mapping techniques were developed•Was used for recording brain wave activity, rather than for imagingAny neuronal activity in the brain generates electric current flowCurrent flows through the cranium and scalpThe changes in electric potential are detected by electrodes placed on the scalpEEG MappingNowadays multiple electrodes can be placed all over the scalp, allowing the recording of the electric activity from many different sites simultaneouslyAllows the construction of topographic maps of the momentary electric activity on the scalp Also permits study of the time series of these maps with millisecond resolution•But very poor spatial resolutionMultiple electrodes for mappinghttp://brainmapping.unige.ch/researchtopics.phpERP MappingERP – event related potentialsTraditional analysis: ERP waveforms at certain electrode positionsERP mapping attempts to determine points in time when map configurations change and/or when they differ between experimental conditions Relies on the fact that, whenever the spatial configuration of the electric field on the scalp differs, different neuronal populations are active in the brain, reflecting an alteration of the functional state of the brain Christoph M. Michel, Margitta Seeck and Theodor Landis, Spatiotemporal Dynamics of Human Cognition News Physiol. Sci 1999 Oct, 14:206-214EEG-MRI CoregistrationSeparate MRI images are takenReference points are used to get same positioning•Impossible to get them accurate•But can get within a few mmEEG-MRI Co-registration•Spinelli L, Gonzalez Andino S, Lantz G, Seeck M, Michel CM. Electromagnetic inverse solutions in anatomically