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Chapter 3

Human Brain - Chapter 3.docx

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Ted Petit

Chapter 3 – Techniques in Neuropsychology MODULE: Study of Damaged Nervous System The Scientific Mind - brain and beh can be investigated in at a variety of complexities and time scales which depend primarily on the question that is being investigated - some questions > minutiae of their properties others by their nature - scientific method > objective and replication or confirmation of results - standardized tests and measurements - empirical method, replication [so initial results did not occur by chance and generalizable] - best term to describe the scientific method > control, o refers to the ability to manipulate something of interest and determine its effects o the ability to exclude unwanted variable [confounding variables] o appropriate comparison sample so deviations can be observed - hypothesis directs the research [statement that can be rejected] o eliminates vague question o avoids questions that cannot be disproved - independent [manipulated] and dependent variables [response beh] - much of research in neuropsychology is quasi-experimental > ethically and practically we cannot manipulate the independent variable directly - may be few of the kinds of people we want to see, man confounding var - cannot rely on single experiment for conclusions - we rely on convering operations > a common conclusion is reached by examining a # of studies that approach the question in a variety of diff perspectives [if consensus > confident we have learned an imp feature] Nonhuman Animal Models - 1930-65, dominated by the study of white lab rats - assumption that there are minimal basic diff btwn most mammals - nonhuman studies > allowed to control all of the aspects of the life cycle o greater objectivity and precision that is not in human experiments - now know imp diff among species which also tells us something - reduces variability that is attributable to extraneous variables - allows for random selection - can isolate causal conclusions - examination of discrete lesions >insight into relationship brain and beh - Tinberg > imprinting and that of Diamond effects on enriched enviro - teratogenic/beh effects of alcohol was first done in nonhuman animals - limitations > focus on one facet of the organism and ignore the others o delayed nonmatching to sample task > after observing reqrd paired with stimulus A, then one is required to pick a novel stimulus to receive the reward o ethological validity> do animals exhibit this beh in natural setting o tasks may be so novel > do not provide info on real world func o not easily generalizable to other species [human too complicated at time may be better to examine simpler systems] - nonhuman animal experimentation has provided critical info regarding how, why, and where psychological phenomena such as learning occur within the nervous system - mammalian systems are remarkably conserved > great degree of overlap among basic properties of the nervous system - thus, at the most basic level of life, DNA, there is remarkable conservation of systems across species and the understanding of how one species solves a prob posed b the enviro may lead to understanding other solutions to the same prob - learning principles generalize to other species > humans included - cogn not generalize to humans - semantic categorization > pigeons, rats, chimps, gorillas, parrots o suggest > unlikely that lang is developed in a ontogenic and phylogenic isolation form other cogn abilities - limitations > important diff btwn mammalian species [complexity of NS] o some questions are quite difficult to in humans not to mention nonhuman animals > consciousness Cognitive Testing - Mini-mental state exam > how well people answer a series of question o designed to examine cogn func > lang, orientation ot location, attention, orientations to time - ppl w/ injury first beh test in emergency room - neurological not as detailed as neuropsychological > but give gross appreciation to the degree to which the NS is involved in a injury - this is a generalization but only trying to see the degree basic neurological func have been affeed - neuropsychological testing is a detailed examination of higher cognitive functions o personal interview > medical history, probs/concerns o series of tests > standardized cogn tests [given in same way to everyone and always score din the same manner] o test of general cogn > specific cogn func - used to help in diagnosis, intervention and rehabilitation - limitations > if not given/scored standardized manner > meaningless - some test have issues in generalizablity MODULE: Brain Imaging - current neuroimaging techniques have technical and methodological limitations [no ultimate investigative tool] - the type of tool used must suit the problem to be sovled - common problem > everyones brain is different o might demostrate similar patterns of activiation but the boundaries of functional brain areas are not exactly the same location for everyone  average? or each separately? Structural imaging - image of the structure of the brain > before lots of tests - inform about location of abnormalities - beh assessments now > rehabilitation, management of deficits - paradigm shift > initiated by the 1960s x-ray combined with computer X-Rays - neuroradiology > studying the NS w/ imaging made possible by serendipitous discovery by Wilhelm Conrad Rontgen - X-rays > cannot pass through all material with the same ease - medical > less dense body parts absorb less and vice versa o thus the amount of radiation that passes through a region provides a measure of the density of the structures within the region - principle: send a beam of X-rays into a structure > see how many stick by detecting the oens that pass through on a photographic plate o more dense > lighter [2D] - allowed ot look for pathology in noninvasive way - h levels of x-rays also used to destroy unwanted tissues - conventional x-rays not useful for neural imaging > soft tissue encased in bone> only give info about entry wound not what has occurred inside skull - cannot differentiate btwn CSF and brain structures Computed Tomography [CT] - 1 good way to image live brain tissue - 1960/70s > combined x-rays and computing - uses same radiation and methods as X-ray but CT involves the projection of x-rays from multiple angles followed by the computerized reconstruction of the measures into 3D images - reasonably accurate 3D representation - constructed in slices > 9-12 per scan - spatial resolution is adequate from clinical purposes - ability to differentiate btwn grey/white matter is poor - painless, little time, can be done on unconscious person - lie flat on bed > slide into scanners x-ray source and detector arrays > array rotates > images can be computed in any of 3 planes - CAT scan > images being constructed on the axial plane [run parallel w/ the horizon] - now all 3 planes used - coronal plane > slices perpendicular to the horizon, taken along the superior-inferior axis - sagittal plane > perpendicular to the horizon, taken along the dorsal-ventral axis o useful in clinical and research applications o in clinical shows abnormalities if they are reflected in changes in tissue density [not always the case] - multi-infarct dementia rarely diagnosed before CT - revolutionized research > didn’t have to wait to do autopsy to see deficits Magnetic Resonance Imaging [MRI] - Felix Bloch and Edward Purcell > based on nuclear magnetic precision measurement - fundamentally diff in the ways CT and MRI image the brain - MRI > replace CT due to superior resolution - exploits the fact elements can be influenced by magnetic fields - hydrogen > normally atoms not polarized > magnetic field > polarizes all in same direction and > once aligned can be perturbed in a uniform direction through the application of a radio freq pulse - diff pulse freq are better at perturbing hydrogen atoms w/I diff types of substances, depending on what you want to see - MRi machine measures reaction time that follows the pulse > which is the time taken by the atoms to return to their normal, random state - MRI’s receiver coil measures the info about the intensity of the signal but the spatial info is provided from variations in the gradient field over the imaged area [combo of these type of info allows > 3D images
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