RESUMO
In this paper, the topology of cortical visuotopic maps in adult primates is reviewed, with emphasis on recent studies. The observed visuotopic organisation can be summarised with reference to two basic rules. First, adjacent radial columns in the cortex represent partially overlapping regions of the visual field, irrespective of whether these columns are part of the same or different cortical areas. This primary rule is seldom, if ever, violated. Second, adjacent regions of the visual field tend to be represented in adjacent radial columns of a same area. This rule is not as rigid as the first, as many cortical areas form discontinuous, second-order representations of the visual field. A developmental model based on these physiological observations, and on comparative studies of cortical organisation, is then proposed, in order to explain how a combination of molecular specification steps and activity-driven processes can generate the variety of visuotopic organisations observed in adult cortex
Assuntos
Animais , Evolução Biológica , Córtex Cerebral , Campos Visuais , Vias Visuais , Mapeamento Encefálico , Córtex Cerebral , Modelos Neurológicos , PrimatasRESUMO
In this paper, the topology of cortical visuotopic maps in adult primates is reviewed, with emphasis on recent studies. The observed visuotopic organisation can be summarised with reference to two basic rules. First, adjacent radial columns in the cortex represent partially overlapping regions of the visual field, irrespective of whether these columns are part of the same or different cortical areas. This primary rule is seldom, if ever, violated. Second, adjacent regions of the visual field tend to be represented in adjacent radial columns of a same area. This rule is not as rigid as the first, as many cortical areas form discontinuous, second-order representations of the visual field. A developmental model based on these physiological observations, and on comparative studies of cortical organisation, is then proposed, in order to explain how a combination of molecular specification steps and activity-driven processes can generate the variety of visuotopic organisations observed in adult cortex.
Assuntos
Evolução Biológica , Córtex Cerebral/fisiologia , Campos Visuais/fisiologia , Vias Visuais/fisiologia , Animais , Mapeamento Encefálico , Córtex Cerebral/anatomia & histologia , Modelos Neurológicos , PrimatasRESUMO
1. The topographic organization of the cortical visual areas in the Cebus monkey and their anatomical connections support the subdivision of the visuaol pathways into ventral and dorsal streams of visual information provessing. 2. We propose that the dorsal stream, as defined by Ungerleider and Mishkin (In: Ingle DJ, Goodale MA and Mansfield RJW (Editors), Analysis of Visual Behavior, MIT Press, Boston, 1982), be subdivided into dorsolateral and dorsomedial streams, which are concerned with different aspects of the processing of motion and spatial perception. 3. The data support the hypothesis of concurrent, modular processing of visual attributes in cortical visual areas in the different streams, and highlight some features of the visual field representation in each area which may reflect functional specialization of these streams. 4. The visual topography is locally disrupted in some cortical areas by the existence of functionally different modules, However, a global visuotopic organization is preserved in most areas. 5. The visuotopic organization may provide the address of space coordinates to integrate information concerning the same retinotopic across different visual areas
Assuntos
Animais , Córtex Visual/anatomia & histologia , Campos Visuais , Vias Visuais/anatomia & histologia , Cebus/anatomia & histologia , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Histocitoquímica , Córtex Visual/enzimologiaRESUMO
The normal pattern of cytochrome oxidase (CO) activity in the posterior cortical areas of the South American opossum (Didelphis marsupialis aurita) was assessed both in horizontal section of flattened cortices and in transversal cortical sextions. the tangential distribution of CO activity was uniformly high in the strate cortex. In the peristriate region alternating bands of dense and weak staining occupied all the cortical layers with the exception of layer I. This observation suggests the existence of a functional segregation of visual processing in the peristriate cortex of the opossum similar to that present in phylogenetically more recent groups