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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) - PowerPoint PPT Presentation
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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+
-
TIME (sec)0 21
SHOE
AVERAGE
What do ERP waveforms tell us?
CONDITION A
CONDITION B
0 1 2
TIME (seconds)
5uV+
-
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