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 1 o 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, 15 O 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
Signal Averaging Event-related Potentials (ERPs)! Background EEG signal can be removed by trial-averaging revealing the response of a brain region to stimuli
Averaging EEG produces ERPs DOG SHOE AIR AVERAGE + 10uV - 0 1 2 TIME (sec) Portions of the EEG time-locked to an event are averaged together, extracting the neural signature for the event.
What do ERP waveforms tell us? + 5uV - CONDITION A CONDITION B ONSET OF EVENT 0 1 2 TIME (seconds) INFORMATION ABOUT THE NEURAL BASIS OF PROCESSING IS PROVIDED BY THE DIFFERENCE IN 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
Transgenic mice Genetic Engineering! Gene Knockout Techniques! Gene Replacement Techniques
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