HIPPOCAMPAL COMMISSURE FUNCTION AND ANATOMY

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Much contemporary work focuses on the hippocampus as a structure of unique importance for memory. It is thus of obvious interest to understand what information passes from one hemisphere to the other by way of the hippocampal commissure (HC). Examination of this question, however, has heretofore been deemed unapproachable because of the close adherence of the dorsal HC (dHC) to the overlying corpus callosum (CC) and insufficient knowledge about the connectivities of the fibers that constitute the dHC and contiguous parts of the CC. This impracticality is now relieved by emerging understanding of the relevant interhemispheric pathways, which suggest a new surgical strategy, devised and tested in this laboratory on macaques, that will permit testing interhemispheric transfer of visual/mnemonic information across the dHC in isolation, or in conjunction with the splenium of the CC. The dHC-splenium combination has already been extensively studied in this regard; however, it is entirely unknown whether the dHC shares, duplicates, or augments the capabilities of the splenium or, indeed, whether it accounts for some of the properties previously attributed to the latter. The transfer to one hemisphere of visual discriminations learned by the other and interhemispheric recognition of previously presented visual images will be tested; and, in the same animals, the complex origin and destination of fibers that constitute the dHC, splenium, and anterior commissure-all of which have components arising in common from the parahippocampal gyrus-will be examined. The results should advance understanding of interhemispheric processes and their relation to memory. Moreover, since interhemispheric processing has been shown to be abnormal in schizophrenia, the results will contribute fundamental information pertinent to understanding of some of the symptoms of this complex mental disorder.