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Chapter 5

chapter 5 - biopsych.doc

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Paul Mallet

Chapter 5The Research Methods of BiopsychologyThe ironic case of professor ptwo weeks before brain surgery went to hospital for series of testsseemed very familiarhad brain tumor on right auditoryvestibular cranial nervehad to have it excised cut outbalance vestibular function was tested by injecting cold water into his earsaid he felt a cold earhearing in right ear was poorright vestibular nerve was barely functioningone last testskin on right cheek was lightly pricked while EEG responses of somatosensory cortex were recorded from his scalpone main risk of removing tumors on auditoryvestibular cranial nerve is damaging the facial cranial nerve and that would make the right side of your face sagMethods of studying the nervous systemMethods of visualizing and stimulating the living human brainbefore 1970sbiopsychological research was impeded by the inability to obtain images of the organ of primary interesthuman brainconventional xray photographyuseless for this purposexray photography is effective in characterizing internal structures that differ substantially from their surroundings in the degree to which they absorb xraysie a revolver in a suitcase full of clothes or a bone in fleshby the time an xray beam has passed through numerous overlapping structures of the brain it carries little info about the structures through which it has passedContrast xraysuseful for visualizing the braininvolve injecting into one compartment of the body a substance that absorbs xrays either less than or more than surrounding tissueinjected substance heightens the contrast between the compartment and surrounding tissue during xray photography cerebral angiographyuses infusion of a radioopaque dye into a cerebral artery to visualize the cerebral circulatory system during xray photographymost useful for localizing vascular damagedisplacement of blood vessels from their normal position can indicate the location of a tumor Xray computed tomographyearly 1970sstudy of living human brain was revolutionized by intro of computed tomographyCTcomputerassisted xray procedure that can be used to visualize the brain and other internal structures of the living bodyduring cerebral computed tomographyneurological patient lies with hisher head positioned in center of a large cylinderone sidexray tube that projects xray beam through head to xray detector mounted on other sidexray tube and detector automatically rotate around head of patient at one level of brain taking many individual xray photos as they rotatemeager info in each xray photo is combined by computer to generate a CT scan of one horizontal section of brainthen xray tube and detector are moved along the axis of the patients body to another level of the brain and the process is repeatedscans of eight or nine horizontal brain sections are typically obtained from patientcombinedthey give a 3D representation of brainMagnetic resonance imaginghighresolution images are constructed from the measurement of waves that hydrogen atoms emit when they are activated by radiofrequency waves in magnetic fieldMRI gives clearer images of brain than CTgives high spatial resolution ability to detect and represent differences in spatial locationcan produce figures in 3DPositron emission tomographyPET scanfirst brainimaging technique to provide images of brain actively functional brain images rather than images of brain structure structural brain images2deoxyglucose2DGinjected into patients carotid artery artery of neck that feeds the ipsilateral cerebral hemisphereFunctional MRImost influential tool of cognitive neurosciencewidely used for medical diagnosisproduces images representing increase in oxygen flow in blood to active areas of brainpossible because of two attributes of oxygenated blood1 active areas of brain take up more oxygenated blood than they need for their energy requirementsoxygenated blood accumulates in active areas of brain2 oxygenated blood has magnetic propertiesoxygen influences effect of magnetic fields on iron in bloodsignal recorded by fMRI is called BOLD signal bloodoxygenleveldependent signal4 advantages over PET1 nothing has to be injected into the subject2 provides both structural and functional info in same image3 spatial resolution is better
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