STRATEGIES OF COGNITIVE NEUROSCIENCE The Coin of the Realm: correlations between psychological and neurophysiological events/structures Establishing two-way constraints between levels –Cognitive psychology as the bootstrap –Neuroactivity as the bootstrap Regions of interest (ROI’s) and localization of function –Subtractive versus parametric designs Covariation and functional networks –Patterns of correlated activity –Principal Component Analysis –Structural Equation Modeling

IMAGING THE MIND Direct methods –Electrical activity (EEG, MEG) –Metabolic activity (EROS) Indirect methods –Changes in regional Cerebral Blood Flow (rCBF) (PET, MRI, fMRI) Method Temp Resol Spatial ResolDepth Tech DifficCost EEG PoorMod ERP ExcelMod PET PoorModGoodHigh Blocked fMRI PoorExcel High Event-Rel fMRI GoodExcel High MEGExcelGood if Tang ModHigh EROS Excel Mod Low

EEG and EVENT-RELATED POTENTIALS (ERPs) Postsynaptic extracellular potentials vary with neuronal activity Masses of pyramidal cells generate a varying electrical signal, the EEG Changes in the EEG that are related to psychological events (ERPs) can be seen by averaging Various ERP “components” are sensitive to memory processes

MAGNETOENCEPHALOGRAPHY methodology –Incredibly weak magnetic signal (femtoTeslas) –Detected by SQUID ($3M, 16,000 lbs, minus 269 deg C –Works for neural fields tangental to surface

MEG analysis Observing moving stimulus Closeup of Dipole:

EVENT-RELATED OPTICAL SIGNALING (EROS) Infrared light source placed on scalp Scattered light picked up by optic detector Signal varies with metabolic state of neurons

PET IMAGING Subject ingests radioactive tracer Does cognitive task for several minutes Metabolic activity increases regional cerebral blood flow in specific areas Tracer is deposited more in these areas than others Isotopes decay and emit positrons These are detected and an image of activity reconstructed

MAGENTIC RESONANCE IMAGING (MRI) Align the spins of Water-based hydrogen atoms by powerful magnetic field Create a “gradient” in the field “pulse” the field with a strong radio- frequency signal that perturbs the alignment Using an RF detector, track the return to alignment With really complex computing, reconstruct the 3D density of tissue in the brain

HISTORY OF MRI NMR = nuclear magnetic resonance Felix Block and Edward Purcell 1946: atomic nuclei absorb and re-emit radio frequency energy 1952: Nobel prize in physics nuclear: properties of nuclei of atoms magnetic: magnetic field required resonance: interaction between magnetic field and radio frequency MRI -1973: Lauterbur suggests NMR could be used to form images -1977: clinical MRI scanner patented -1977: Mansfield proposes echo-planar imaging (EPI) to acquire images faster fMRI -1990: Ogawa observes BOLD effect with T2* blood vessels became more visible as blood oxygen decreased -1991: Belliveau observes first functional images using a contrast agent -1992: Ogawa & Kwong publish first functional images using BOLD signal From Dacnker, 03 webcourse

FUNCTIONAL MAGNETIC RESONANCE IMAGING (fMRI) Oxygenated blood has different magnetic properties than deoxy So comparing MRI between target task and “control” task (a challenge) reveals areas of task-related activation

Blood Oxygen Level Dependent (BOLD) Response From Doug Noll tutorial

fMRI (cont’d) Event-related fMRI allows tracking of the “hemodynamic response” to individual events: Source: Kwong et al., 1992