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Lecture 4

Lecture 4 on Methods - PSY290 - Oct 1/2013

11 Pages

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John Yeomans

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 Trying to relate human psychology to neurology  Cognitive neurology --> how thinking/cognition change after injury --> now done by detailed analysis by studying behaviour (change in function)  Visualizing brain structurally --> *major part of neurology  How physics used to visualize chemical, electo (electroencephalography), aspects of brain --> PET, MRI, CT scans  Other major approach to studying brain = going into brain --> mostly involves animals (can’t do invasive techniques w/humans) -->*rodents --> combined with:  Animal psychology --> need to use neurochem and pharmacology --> the biopsychological approach (invasive techniques on animals)  We talked about recording from single neurons from single dish --> studying act poten, neuron Δes  Neurophysioology in humans --> electrodes onto surface of, or within (req. Surgery), human head Overall imaging in human brain --X rays:  Began 1800’s  Absorbtion of x-rays occurs mainly in bones --> thus imaging shows powerfully bone tissue  Head: visualize cranium --> grey matter & white matter vs. Ventricles  90% absorption in skull  Ventricles less absorbing of x-rays than skull  Best way--shooting x-rays from behind (back of brain) --> visualize ventricles in contrast w/brain  Can visualize skull, shadow of ventricles  Some things in brain absorb xrays well --> hematomas (thicker than brain tissue --can see thickening of brain during blood clot --> will see it as darker tissue --> e.g. Subdural hematoma  Thicker than grey matter --> e.g. Ventricles  Tumors harder to see unless calcified --> +Ca will absorb more x-ray (like skull material)  Method used until 60s  After which, CT discovered as better internal visualization of internal brain structures CT Scans:  6 different angles  8-9 images taken  & calculate maount of absorption --> beetter estimate of thickness of tissue  How much absorption on outside v inside  Gives internal pic of brain by taking X-ray absorption from 6 different angles  How much absorption fro outer cranium v inner tissue  Very good resolution  Better for brain injuries or tumors  ~$1mill  3D picture for deep brain density --> using several depths or sensors  “computer  assisted tomography” -- ‘tomography’= ’picture’ of a ‘slice’ Thus, thickness doesn’t necessarily equal function Cerebral Angiogram:  Can inject thick material into cerebral artery --> carried up brain through carotid artery --> smaller artery in cerebral cortex  If blockage, arteries missing  X-ray dense material placed in arteries --> see which arteries blocked --> *anticipate or look for stroke causers  Where stroke is  Measures effectiveness of blood thinners for unblockage  PROBLEM: doesn’t see grey/white matter --> similar density --> seeing internal structures MRI:  Based on spin of certain elements (H* most important)  Can spin H molecules -- emit radiowave→ signals where it is most densely concentrated  Not measuring thickness/mass of brain, but density of H molecules  Concentrated according to tissue --> water high content, therefore high content of H found --> will highlight certain areas of brain  High resolution --> much better imaging of internal brain structures  10x more expensive than CT scan Another method: Blood-oxygenation (hemoglobin oxygenation) This was structural imaging. Recording Brain/neural activity:  Most single act potentials involve micro-electrodes (puncture cell w/tiny micron tip)  Must go into brain to study activity  Larger electrodes -- evoked potentials (for whole nerve/brain region) --> not single neuron activity  If electrodes on surface of brain --> EEG --> records large brain regions (rough estimate of where things are happening)  Advantages: Better temporal resolution, though poor spatial resolution  E.g.:  Can’t see post-action potential (top left)  Top right--See extracellular action potentials--caused by average synaptic potential (e.g. Excitatory/inhibitory) --most slow potentials are not fast spikes  Bottom right --> usually recorded from whole lobe, poor spatial resolution, but can record millisecond changes w/ good temporal resolution but bad spatial resolution FUNCTIONAL IMAGING:  EEG--patients cannot move other facial muscles--interferes w/activity of brain  EMG--electromyogram--when muscle moves, big burst of activity  ECG--electrocardiograph  MEG--muscles underneath skin  Muscles have large action potentials --> produce large waves of electrical activity  Recent new methods for measuring brain activity  When brain active --> increased metabolism --> need more energy, need glucose and O 2O b2rns glucose --> en ) -  2-Deoxyglucose (injection) method  In animals --” inject 2DG into brain (deoxyglucose techniuqe)  Then apply method to humans: --> Calculate amount of Positron emissions -- identify regions of internal brain activity -- PET scans Now, BOLD method of fMRI = more common method of measuring activity PET scans --> localized brain activity --> where chemical (e.g. Dopamine) is acting  Where chemistry of brain is Δing  Not as accurate as fMRI, and expensive, but still useful  Look at transmitters and receptors (chemical signals--dopamine)  Are stronger emissions*--> Limit of radioactive dosage --> cannot do repeated testing and not as frequent as fMRI fMRI --> more versatile, no worries about radioactive dosage  fMRIs (3D) — anterior cingulate cortex  Compare many images --> can do much subtraction (sub A from B; vice versa)  Big advantage of EEGs --> see changes happening quickly  E.g. Seizures --> see it as series of spikes 10x bigger than normal --> intense electrical activity  Normal brain activity (20-50 micro-volts) --> very small waves  Brain changes when falling asleep is interesting  When aroused, signals have low amplitude (40+ gamm
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