The Aging Mind Opportunities in Cognitive Research (2000) / Chapter Skim
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Appendix G: Functional Magnetic Resonance Imaging of the Brain in Nonhuman Primates: A Prospectus for Research on Aging
Appendix G: Functional Magnetic Resonance Imaging of the Brain in Nonhuman Primates: A Prospectus for Research on Aging
Pages 238-250
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From page 238... ...
This technique exploits variations in magnetic susceptibility that arise from molecular binding of oxygen to hemoglobin, which can be used to detect blood flow changes associated with neuronal activity. These neuronal activity-related signals can be isolated with a spatial resolution (1-2 mm)
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From page 239... ...
Indeed, this is an area of tremendous potential owing to the unprecedented ability offered by fMRI to identify specific brain abnormalities associated with age-related sensory, motor, memory, and language dysfunction. LIMITATIONS OF TORI FOR STUDIES OF THE HUMAN BRAIN The reasons for the rapid development of fMRI techniques and their application in studies of human brain function are obvious.
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From page 240... ...
In the near future it will also be possible to extend this genetic approach to other species, including nonhuman primates, by exploiting the capacity of genetically engineered viruses to introduce novel genes into the brains of adult animals. Moreover, this pairing of techniques from molecular biology and functional imaging will provide a powerful means to investigate both the contributions of specific cells or cellular components to age-related changes in brain function and to evaluate genetic intervention as a means to influence the course of such changes.
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From page 241... ...
, in contrast, is a potentially attractive subject for study because of its small size, rapid aging, and ease of breeding. Such benefits must, of course, be weighed against the fact that there are far fewer details known of brain anatomy and physiology in these species in comparison with macaques, but a case can sometimes be made for their use in studies of the aging brain and, hence, for fMRI studies of aging in nonhuman primates.
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From page 242... ...
Evaluation of Cellular Events That Underlie the Vascular Signals of fMRI The fMRI technique enables quantification of local changes in cerebral blood flow. The use of these measures as an index of neuronal function is predicated on the assumption that there is a specific relationship between neuronal activity and the magnitude of the hemodynamic response.
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From page 243... ...
fMRI will allow an unprecedented comparison of functional activity patterns in monkeys and humans engaged in identical tasks, which will, in turn, permit identification of functional homologies and the ability to directly relate the vast literature on cellular response properties in monkeys to the field of human neuropsychology. Use of fMRI as an Adjunct to Traditional Methods Used in Nonhuman Primates There remains much to be gained from the application in nonhuman primates of traditional experimental techniques, such as single-cell electrophysiology, anatomical tract tracing, and behavioral analyses of the effects of focal brain lesions.
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From page 244... ...
Data informative of the correlation between MR signal and the activity of specific cell populations can be obtained only in nonhuman species. Use of fMRI Signals to Guide and Evaluate Manipulation/Intervention Studies Because fMRI reflects neuronal activity with good spatial and temporal precision, it promises to be a valuable tool for the identification and characterization of age-related loss of function and specific brain pathologies.
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From page 245... ...
First, to exploit the potential of fMRI in nonhuman primates, the experimenter must extract a measure of the subject's sensory, perceptual, or cognitive state, which can only be accomplished via some sort of behavioral response. Audible magnet noise is distracting and/or annoying to such a degree that it can interfere with expected cognitive events and the performance of animals on complex behavioral tasks.
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From page 246... ...
The MR signal was measured in the visual cortex in response to a stimulus known to elicit robust responses from individual cortical neurons. The MR measurements were low resolution and intentionally nonspecific, but cortical MR signals were robust and confined to regions known to exhibit significant neuronal responses to the stimuli presented.
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From page 247... ...
Despite these welcome advances, fMRI will never replace cellular electrophysiology as a means to investigate the neural foundations of cognitive function there are physical upper bounds on the spatial and temporal resolution that can be achieved. However, as summarized above, fMRI is an extremely valuable complement to more conventional cellular studies of neuronal activation and patterns of connectivity.
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From page 248... ...
Consider, for example, the hypothesis that one aspect of age-related cognitive decline is linked to down-regulation of a specific subtype of postsynaptic neurotransmitter receptor in a specific brain region. fMRI data obtained from aged nonhuman primates confirms that the activity level in that
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From page 249... ...
REFERENCES Chen, W., and K Ugurbil 1999 High spatial resolution functional magnetic resonance imaging at very-high magnetic field.
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From page 250... ...
Orban 1998 Functional magnetic resonance imaging in an awake rhesus monkey. Society for Neuroscience Abstracts 24:11.
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