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The neuroanatomy of extrastriate area 19 : a modular mosaic Stewart, Tara H.


Studies of the primary visual cortex of the cat have been essential in establishing features of visual cortical organization that are fundamental to all mammalian species. One feature discovered in the cat is the presence of separate pathways that process different aspects of visual space in parallel. These parallel pathways can be defined by their organization with respect to the punctate pattern of cytochrome oxidase (CO) staining in the primary visual cortex (i.e. CO blob versus interblob). The extrastriate areas of the cat however, have not enjoyed such close scrutiny and the relationship between these areas and the parallel pathways is unknown. The aim of this study is to examine the modular organization of extrastriate area 19 (defined as a modular mosaic) in order to identify features which are shared with other mammalian species and which may be critical to overall extrastriate organization and function. Specifically, this study demonstrates that cells located in both the CO blobs and interblobs project to area 19, but they project to different regions or modules within area 19. Furthermore, it is found that intrinsic connections within area 19 form a patchy network. Two of the main recipients of projections from 19 are extrastriate areas LS and 21a. These two areas are distinguished physiologically: LS is responsive to motion, while 21a is sensitive to form (Dreher et al., 1996a). This study found that cells in area 19 that project to either 21a, or LS are organized in bands, which have spacing larger than the intrinsic patches. The bulk of the 21a and LS projection bands interdigitate, however regions that are less densely labeled tend to overlap. The characterization the contribution of parallel pathways to the modular mosaic in area 19 identifies several features of extrastriate cortical organization that may be shared by other mammals. First, the parallel pathways are not limited to the primary visual cortex but extend into extrastriate cortex. Second, these pathways are only partially segregated and with regions of convergence; this pattern is important, as it would allow for the efficiency of parallel processing while providing communication between the separate pathways.

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