Brain and Cognition Some New Technologies (1989) / Chapter Skim
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3. Four New Technologies: Research Findings
3. Four New Technologies: Research Findings
Pages 18-42
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From page 18... ...
Research opportunities are discussed in terms of the conceptual foundations estate fished by the current research and the technological breakthroughs that make possible finer definition of brain functions involved in cognitive processes. One unport ant and general conclusion emerges from these discussions, namely the importance of exploiting the complementary advantages of the different technologies as, for example, employing both PET and MRl methodologies for solving problems of anatomical localization of physiological processes.
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From page 19... ...
Background of Researth Fm~mgs The ERPs provide a rich class of responses that may, within the appropriate research paradigm, allow the study of processes that are not readily accessible to experimental psychologists by other means. The key assumption of cognitive psychophysiology ~ that ERP components are manifestations at the scalp of the activity of specific intracranial processors.
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From page 20... ...
Likelihood That Progress WiB be Made The ensemble of information-processing activities manifested by the ERPs is already quite rich. Additional components are being discovered and deeper understanding is being reached of components that have been known since the 1960s.
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From page 21... ...
Thus, for example, there ~ considerable interest ~ the role that these negative components play in studies of lexical decision (Nastanen, 1982~. P30~A Manifestation of Strategic Proce - sing When subjects are presented with events that are both task relevant and rare, a prominent positive component with a latency of at least 300 msec is elicited.
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From page 22... ...
The Readmese Potential and the Contmgent Negative Variation—Preparation to Respond Kornhuber and Deecke (1965) have shown that voluntary responses are preceded by a slow negative wave, which they labeled the readiness potential (RP)
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From page 23... ...
The work in humans using indwelling electrodes, neuromagnetic recording, and clinical observations on the effects of lesions (Johnson and Fedio, 1986) is likely to combine in the near future with the work in animals to yield much deeper understanding of the neurophysiological basis of the ERPs.
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From page 24... ...
Methodological Moues Data acquisition is not a source of serious problems in ERP research, depending as it does on established technologies. However, experimental design, measurement, and data analysis present serious challenges that require attention.
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From page 25... ...
These Brain maps represent the changing pattern of activity at varying points In tone in a two-dimensional and easily visualizable display. However, all the mapping techniques discussed in this report, including brain mapping, would greatly benefit from an effort to develop statistical methods that can cope with this complex data base.
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From page 26... ...
This led almost immediately to the notion that the mapped field could be compared with that which would be produced by an equivalent current dipole source, and the source could be located within the three-dimensional volume of the brain. The magnetic field is associated with the intracellular currents of a limited population of neurons in the brain.
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From page 27... ...
It quickly became apparent that multiple sensors would be necessary to realize the full potential of the technique. The main advantage of magnetic recording Is that, using a m~nnnum number of assumptions, it is possible to determine the three-~unensional location, geometric orientation, and strength of equivalent current dipole sources.
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From page 28... ...
Since the distribution of intracranial volume currents is strongly influenced by features of the skull such as the orbits of the eyes, the sutures in the skull, and other anisotropies of conductivity, source localization using s~rnple concentric sphere models should be subject to considerable error. If it is true that these same conditions have little effect on the extracranial magnetic fielcI, then relatively simple models of the head should permit excellent source localization.
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From page 29... ...
Such findings lend credence to the strong cIann that the skull and other tissues are essentially transparent to magnetic fields at the frequencies of interest, and measuring these fields avoids some of the problems associated with effects of conductivity differences on the flow of volume currents. Although empirical data such as these are impressive, they do not provide a direct validation of the strong claim regarding source localization.
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From page 31... ...
Furthermore, there was no sign of activity from any other sources such ~ the frontal lobes. The equivalent current dipole sources of the magnetic N100 and P200 were located in or near the auditory cortex.
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From page 32... ...
Still another contribution of ERF studies is the first report that the equivalent current dipole source of the P300 is in or near the hippoca~npal formation (Okada, Kaufman, and Williamson, 1982~. This finding is consistent with data obtained using indwelling electrodes in epileptics.
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From page 33... ...
Animal models and methods of current source density analysis applied to their exposed brains should help to clarify this issue. So too would correlated brain imaging studies (see the next section)
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From page 34... ...
IMAGING TECHNIQUES I: POSITRON EMISSION TOMOGRAPHY Positron emission tomography (PET) is a nuclear medicine technique that produces an image of the distribution of a previously administered radioactively labeled compound in any desired section of the body (Ra~chie, 1983~.
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From page 35... ...
the objective was to use PET measurements of blood flow to locate the regions of the human cerebral cortex concerned with the elementary mental operations of visual and auditory word processing. Four behavioral conditions formed a three-level subtractive hierarchy: passively viewing a cross hairs on a television monitor; passively viewing or hearing single words at one per second; repeating the words; and generating a use for the words.
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From page 36... ...
IMAGING TECHNIQUES II: MAGNETIC RESONANCE IMAGING Magnetic resonance imaging (MRI) is based on the fact that some atomic nuclei act like tiny bar magnets when placed in a magnetic
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From page 37... ...
During recovery from such manipulations, these tiny bar magnets or dipoles Ernst radio frequency signals that contain a great deal of information about their chern~cal environment. Depending on the strength of such signals, unages of sections of the body can be obtained with this technique.
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From page 38... ...
In terms of the doctrine of modularity in cognitive science, the approach hopes to identify brain areas that subserve particular functions as specified in perceptual and cognitive models. With the proliferation of models that become more complex in terms of the processes and subprocesses that are active in perceptual and cognitive processes, the hope has been that new and better brain imaging techniques will assist in a finer-grained identification of the brain areas involved in
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From page 39... ...
It has maintained that discrete deficits following prescribed lesions are managed by the brain site in question. This limitation has given rise to an alternative view of how to gain knowledge about cognition from "broken brains." The second view holds that, since psychological or cognitive processes are widely distributed throughout neural networks, both focal and diffuse brain damage can reveal clues only to the functional structure of cognitive processes; direct clues to brain correlates of cognitive processes are not revealed.
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From page 40... ...
Today, many workers in this field seem uncomfortable vnth the functional maps of the human cortex as they now stand: these maps appear insufficiently differentiated, whereas more accurate maps would reveal highly specialized functional processes correlated to highly circumscribed zones in the cortical mantle. Over the last century, there have been three major obstacles to the development of more highly differentiated functional maps of the human cortex.
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From page 41... ...
These questions might be approachable given techniques allowing us to look beyond the suici to examine the full expanse of the cortical mantle. Opportunities for Basic and Applied Research The next generation of cortical maps should allow identification of landmarks both on the surface of the gyri and within the depths of the suici, permitting measurement of the dimensions of cortical areas and lesions and clarifying the relations of damaged zones to surrounding cortical regions.
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From page 42... ...
Within the context of traditional neuropsychology, MRI combined with flat mapping of the cortical mantle wild begin to provide the kind of greater specificity called for by modern cognitive theories. The discussion in this section is not intended to convey the impression that all that is needed to understand human brain function are more detailed road maps of the human brain, particularly of the neocortex.
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