Structural Organization and Development of Identified Projection Neurons in Primary Visual Cortex

Abstract

A characteristic feature of the mammalian cerebral cortex is that each cortical area has outputs to a number of different cortical and subcortical destinations. Cortical neurons projecting to a given target are situated in distinct cortical layers. In the visual cortex for example, cells projecting to the lateral geniculate nucleus (LGN) are located in layer 6, cells projecting to the superior colliculus are located in layer 5, and many cells in layers 2 and 3 project to other cortical areas (for review see Sefton, 1981; Gilbert, 1983). Because cells in different cortical layers differ in their receptive field properties (for review see Bolz et al., 1989), the segregation of projection neurons into layers reflects the specificity of the cortical output. The functional specialization of cortical output neurons was strikingly illustrated in previous studies showing that even cells within a single cortical layer, but with different projection targets, differ in their dendritic morphology and participate in different intrinsic cortical circuits (Katz, 1987; Hübener and Bolz, 1988; Hübener et al., 1990). The proper development of these efferent projections is therefore critical for the correct functioning of the visual system.