Visuotopic organization of corticocortical connections in the visual system.

Publisher Summary The chapter describes evidence that some corticocortical connections do not follow visuotopic organization and describes a new concept of organization of corticocortical connections in the visual system. Neurons belonging to extrastriate areas and projecting to a given site in area 17 encodes a much larger region of visual field than that collectively represented by their target neurons in area 17. Many parameters of the organization of visual structures, such as receptive field (RF) size and magnification factors are known to vary with eccentricity in the visual field. Because of the impossibility of identifying nonvisuotopic connections with electrical stimulation another technique is used, the temporal cross-correlation. This method is used with success in the retino-geniculo-striate pathway to identify monosynaptically connected pairs of neurons. A column of neurons in area 17 receives convergent input from a network of neurons situated in other cortical areas. Assuming that this convergence is also found at the level of the individual neuron, a neuron of area 17 could therefore be influenced by populations of neurons having different functional characteristics. By switching from one set of such afferents to another for its major source of functional input, a neuron in area 17 could therefore modify considerably its functional characteristics as a spatio-temporal filter.