COGNITIVE
SCIENCE
17
Peeking Inside
The Head
Part 1
Jaime A. Pineda, Ph.D.
Imaging The Living Brain
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Computed Tomography (CT)
Magnetic Resonance Imaging (MRI)
Positron Emission Tomography (PET)
Functional MRI (fMRI)
Electroencephalography (EEG)
Magnetoencephalography (MEG)
CT Scans
(1970s)
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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)
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A strong magnetic field (1030k 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
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Advantages of MRI
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No ionizing radiation exposure
Better spatial resolution
Horizontal, Frontal or Sagittal planes
Disadvantages
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Cost
No metal!
noisier
Hemodynamic Techniques
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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
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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
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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)
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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
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Electroencephalography
(EEG)
Electromyography (EMG)
Electrooculography (EOG)
Electrodermal activity (Skin
Conductance)
Cardiovascular activity
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Heart rate (EKG)
Blood Pressure
Plethysmography
 Electrophysiological Techniques
 EEG
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non-invasive recordings
from an array of scalp
electrodes
Normal
Seizure
Signal Averaging
“Event-related
Potentials (ERPs)”
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Background EEG signal can be removed by trial-averaging
revealing the response of a brain region to stimuli
Averaging EEG produces ERPs
DOG
• Portions of the
EEG time-locked
to an event are
averaged together,
extracting the
neural signature
for the ‘event’.
SHOE
AIR
+
10uV
-
AVERAGE
0
1
TIME (sec)
2
What do ERP waveforms tell us?
ITION
D
N
O
C
+
5uV
-
ON
SE
TO
CON
FE
VE
NT
0
1
TIME (seconds)
2
DITI
A
ON B
INFORMATION
ABOUT THE
NEURAL BASIS
OF PROCESSING
IS PROVIDED BY
THE DIFFERENCE
IN ACTIVITY
Electroencepholography
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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
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Coil placed over target brain region
Cognitive failures recorded
Techniques Used With Nonhuman
Animals
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Stereotaxic Surgery
Lesion Methods
Electrical Stimulation
Electrophysiological
Recording
Lesioning Techniques
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Aspiration lesions
Radio-frequency lesions
Knife cuts
Cryogenic blockade
Chemical Lesions
Neurohistology Techniques
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Fixation, preservation of tissue,
sectioning and staining of tissue
Uses of histological techniques
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Confirming lesion sites or electrode
locations
In combination with neural tracing
techniques (anterograde,
retrograde labeling)
Autoradiography or
Immunohistochemistry
Neurohistology Techniques
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Nissl Stains
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Golgi Stain
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e.g., cresyl violet
cell bodies
whole neurons
Myelin Stains
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myelin
For more info., see web site:
http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab9/Lab9.htm
Electrophysiology Techniques
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Intracellular unit
recording
Extracellular unit
recording
Multiple-unit recording
Patch clamping
Pharmacological Methods
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Measuring Chemical Activity
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2-DG Autoradiography
In vivo microdialysis
Localizing Neurotransmitters and Receptors
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Immunocytochemistry
In situ hybridization
Transgenic mice
Genetic Engineering
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Gene Knockout Techniques
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Gene Replacement Techniques
Behavioral Research Methods
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NEUROPSYCHOLOGICAL TESTING
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Intelligence (e.g., WAIS, WISC)
Verbal Subtests
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Information, digit-span, vocabulary, arithmetic,
comprehension, similarities
Performance Subtests
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Picture-completion, picture-arrangement, block design,
object assembly, digit-symbol substitution
Neuropsychological Testing
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Language (lateralization)
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Sodium amytal test
Dichotic listening test
Language deficits
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Phonology
Syntax
Semantics
Neuropsychological Testing
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Memory
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STM, LTM
Explicit, Implicit
Semantic, Episodic
Frontal Lobe Function
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Wisconsin Card Sorting Task
Animal Behavior Paradigms
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Species-common behaviors
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Aggressive Behaviors
Defensive Behaviors (e.g., anxiety paradigms)
Reproductive Behaviors
Locomotor Activity
Traditional Conditioning Paradigms
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Pavlovian (Classical) Conditioning
Operant Conditioning
Animal Behavior Paradigms
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Open Field Apparatus
Animal Behavior Paradigms
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Operant Conditioning Apparatus
Animal Behavior Paradigms
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Common Learning Paradigms
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Conditioned Taste Aversion
Conditioned Avoidance
Radial Arm Maze
Morris Water Maze
Conditioned Defensive Burying
Animal Behavior Paradigms
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Radial Arm Maze