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 TempResol

SpatialResol Depth

TechDiffic Cost

EEG 

Poor Mod Mod Mod Mod

ERP 

Excel Mod Mod Mod Mod

PET 

Poor Mod Good High High

BlockedfMRI

Poor Excel Excel High High

Event-Rel fMRI

Good Excel Excel High High 

MEG Excel Good ifTang

Mod High High

EROS 

Excel Excel Mod 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 ofDipole:

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 thatperturbs 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 Purcell1946: atomic nuclei absorb and re-emit

radio frequency energy1952: Nobel prize in physics

nuclear: properties of nuclei of atomsmagnetic: magnetic field requiredresonance: 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