COGNITIVE SCIENCE 17

Peeking Inside The Head

Part 1

Jaime A. Pineda, Ph.D.

Imaging The Living Brain

Computed Tomography (CT) Magnetic Resonance Imaging (MRI) Positron Emission Tomography (PET) Functional MRI (fMRI) Electroencephalography (EEG) Magnetoencephalography (MEG)

CT Scans(1970s)

X-ray scanner rotated 1o at a time over 180 o

Contrast agent Computer reconstruction Horizontal sections Reveal structural

abnormalities, such as cortical atrophy or lesions caused by a stroke or trauma.

Computerized Axial Tomography

MRI Scans(1980s)

A strong magnetic field (10-30k X) causes hydrogen atoms to align in the same orientation.

When a radio frequency wave is passed through the head, atomic nuclei emit electromagnetic energy (NMR) as they “relax”.

The MRI scanner is tuned to detect radiation emitted from the hydrogen molecules.

Different types of tissue produce different RF signals

Computer reconstructs image.

MRI vs. CT Scans

Advantages of MRI – No ionizing radiation exposure– Better spatial resolution– Horizontal, Frontal or Sagittal planes

Disadvantages– Cost– No metal!– noisier

Hemodynamic Techniques

Oxygen and glucose are supplied by the blood as fuel for the brain

The brain does not store fuel, so Blood supply changes as needs arise Changes are regionally-specific – following the local

dynamics of neuronal activity within that region These techniques show where “functional activity”

occurs

PET Scans

A positron emitting radionuclide is injected (e.g., 2-deoxyglucose,

15O radioactive oxygen). Positrons interact with electrons

which produce photons (gamma rays) traveling in opposite directions.

PET scanner detects the photons. Computer determines how many

gamma rays from a particular region and a map is made showing areas of high to low activity.

10 mm resolution; invasive

What PET Can Do

PET vs. CT Scans

CT images brain structure. PET images brain function. CT involves absorption of X-rays. PET involves emission of radiation

by an injected or inhaled isotope.

Functional MRI (fMRI)(1990s)

Images brain hemodynamics Blood oxygen level dependent

(BOLD) signal Advantages over PET:

– No injections given– Structure and Function– Shorter imaging time– Better spatial resolution– 3-D images

Check out this website for more info on fMRI methods: http://www.fmri.org/fmri.htm

Brain Regions Impaired by Alcoholism

Non alcoholic Alcoholic

Psychophysiology

Electroencephalography (EEG)

Electromyography (EMG) Electrooculography (EOG) Electrodermal activity (Skin

Conductance) Cardiovascular activity

– Heart rate (EKG)– Blood Pressure– Plethysmography

Electrophysiological Techniques

EEG

non-invasive recordings from an array of scalp electrodes

Normal Seizure

Background EEG signal can be removed by trial-averaging revealing the response of a brain region to stimuli

“Event-related Potentials (ERPs)”

Signal Averaging

Averaging EEG produces ERPs

• Portions of the EEG time-locked to an event are averaged together, extracting the neural signature for the ‘event’.

10uV+

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TIME (sec)0 21

SHOE

AVERAGE

What do ERP waveforms tell us?

CONDITION A

CONDITION B

0 1 2

TIME (seconds)

5uV+

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ONSET OF EVENT

INFORMATION ABOUT THE NEURAL BASIS OF PROCESSING IS PROVIDED BY THE DIFFERENCEIN ACTIVITY

Electroencepholography

Non-invasive High temporal resolution Direct reflection of neuronal activity Less expensive than fMRI or PET Poor spatial localization due to recordings made at

the scalp Better suited to answering questions about “when”

cognitive processes work not “where” they work

Another Electrophysiological Technique

Transcranial Magnetic Stimulation

Coil placed over target brain region Cognitive failures recorded

Techniques Used With Nonhuman Animals

Stereotaxic Surgery Lesion Methods Electrical Stimulation Electrophysiological

Recording

Lesioning Techniques

Aspiration lesions Radio-frequency lesions Knife cuts Cryogenic blockade Chemical Lesions

Neurohistology Techniques

Fixation, preservation of tissue, sectioning and staining of tissue

Uses of histological techniques– Confirming lesion sites or electrode

locations– In combination with neural tracing

techniques (anterograde, retrograde labeling)

– Autoradiography or Immunohistochemistry

Neurohistology Techniques

Nissl Stains – e.g., cresyl violet– cell bodies

Golgi Stain– whole neurons

Myelin Stains– myelin

For more info., see web site:http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab9/Lab9.htm

Electrophysiology Techniques

Intracellular unit recording

Extracellular unit recording

Multiple-unit recording Patch clamping

Pharmacological Methods

Measuring Chemical Activity– 2-DG Autoradiography– In vivo microdialysis

Localizing Neurotransmitters and Receptors– Immunocytochemistry– In situ hybridization

Genetic Engineering

Gene Knockout Techniques

Gene Replacement Techniques

Transgenic mice

Behavioral Research Methods

NEUROPSYCHOLOGICAL TESTING– Intelligence (e.g., WAIS, WISC)– Verbal Subtests

Information, digit-span, vocabulary, arithmetic, comprehension, similarities

– Performance Subtests Picture-completion, picture-arrangement, block design,

object assembly, digit-symbol substitution

Neuropsychological Testing

Language (lateralization)– Sodium amytal test– Dichotic listening test

Language deficits– Phonology– Syntax– Semantics

Neuropsychological Testing

Memory – STM, LTM– Explicit, Implicit– Semantic, Episodic

Frontal Lobe Function – Wisconsin Card Sorting Task

Animal Behavior Paradigms

Species-common behaviors– Aggressive Behaviors– Defensive Behaviors (e.g., anxiety paradigms)– Reproductive Behaviors– Locomotor Activity

Traditional Conditioning Paradigms– Pavlovian (Classical) Conditioning– Operant Conditioning

Animal Behavior Paradigms

Open Field Apparatus

Animal Behavior Paradigms

Operant Conditioning Apparatus

Animal Behavior Paradigms

Common Learning Paradigms– Conditioned Taste Aversion– Conditioned Avoidance– Radial Arm Maze– Morris Water Maze– Conditioned Defensive Burying

Animal Behavior Paradigms

Radial Arm Maze