HEMISPHERIC DISTRIBUTION OF VISUAL MEMORY

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Understanding why and how each of the two human cerebral hemispheres come to possess demonstrably different degrees of intellectual capability, i.e., "hemispheric specialization",' is a challenging problem, of wide import in neurology and psychiatry. A particularly striking example of such specialization is that of the right hemisphere in recognizing faces, a facility, according to the work of Hamilton and Vermeire, that is shared by macaques as well as man. Using "split-brain"macaques, in which each hemisphere can be tested individually, the proposed experiments will use sophisticated imaging and behavioral techniques in an effort to confirm and extend this prior work, and to achieve a more robust expression of this seemingly inherent difference between the hemispheres. In addition, eye movements will be recorded and analyzed to determine whether such hemispheric specialization is reflected in the patterns of image acquisition. It is known that removal of the temporal lobe, prominently including the amygdala, in macaques yields perturbation of scanning eye movements and a pronounced inability visually to recognize stimuli that normally produce a strong emotional response, such as the human presence. This, and much anatomical and physiological data suggest that the amygdala might play a role in facial recognition within the amygdala of one hemisphere to determine whether a selective effect can be demonstrated on recognition of various types of images. Experiments will also be undertaken to learn whether an intact amygdala in one hemisphere can, via interhemispheric pathways, alleviate the deficiency caused by damage to the amygdala in the other hemisphere. Finally, electrophysiological, experiments will seek to define presumed differences in activation of a hemisphere that is "working" on visual mnemonic problems versus a hemisphere that is merely "idle".