On the representation of the visual fields in the LGN and cortex orthograde and retrograde degeneration in the visual system

In the 1920s and 1930s, anatomists (e.g., Brouwer and Zeeman, 1926) studied orthograde projections from the retina to the LGN by making restricted retinal lesions and identifying degenerating fiber terminals in the LGN using the Marchi stain. Geniculocortical projections were studied by making lesions of the primary visual cortex and mapping retrograde degeneration of cells in the LGN (e.g., Clark, 1932). These anatomical studies confirmed that there is an orderly projection from the retina to the LGN and from the LGN to the visual cortex. Neighboring points in the visual fields are represented at neighboring points on the cerebral cortex. In later studies (Van Buren, 1963), it

Figure 1.2. Cajal's drawings showing the cell types in the mammalian retina. This is Cajal's description (from Thorpe and Glickstein's 1972 translation). All figures show cells from the mammalian retina with the exception of Fig. 1, which shows the nerve cells from the chicken retina.

Fig. 1. A, ganglion cell destined for the first sublayer; B, ganglion cell destined for the second sublayer; C, small ganglion cells with granular clusters which spread in the fourth sublayer; D, multipolar cell destined for the second sublayer; E, a cell which forms two horizontal plexuses—one below the fourth sublayer and another in the third sublayer; F, small cell with two fine plexuses—one in the second sublayer and the other in the fourth sublayer; G, giant cell which forms three plexuses—in the second, third, and fourth sublayers; H, bistratified amacrine cell; J, cell with an extremely fine plexus destined for the third sublayer; K, cell which arborizes in the fourth sublayer and whose branches interlace with the end branches of an amacrine cell lying in the same layer; a, centrifugal fibers; b, another centrifugal fiber whose termination extends horizontally above the inner plexiform layer.

Fig. 2. A section through the retina of an adult dog. a, cone fiber; b, cell body and fiber of a rod; c, bipolar cell with an ascending cluster destined for the rods; d, very small bipolar cell for the rods with a spare upper cluster; e, bipolar cell with a flat cluster destined for the cones; f, giant bipolar cell with a flat cluster; h, diffuse amacrine cell whose varicose branches lie, for the most part, just above the ganglion cells; i, ascending nerve fibrils; j, centrifugal fibers; g, special cells which are very rarely impregnated; they have an ascending axis cylinder; n, ganglion cell which receives the terminal cluster of a bipolar cell destined for the rods; m, nerve fiber which disappears in the inner plexiform layer; p, nerve fiber of the optic fiber layer. A, outer plexiform layer; B, inner plexiform layer.

Fig. 3. Horizontal cells from the adult dog retina. A, outer horizontal cell; B, middle-sized inner horizontal cell with no descending protoplasmic processes; C, another, smaller inner horizontal cell; a, horizontal cell axis cylinder.

Fig. 4. Nerve cells from the ox retina. a, bipolar cell with an ascending cluster; b, bipolar cell with a flat upper terminal cluster destined for the cones; c, d, e, bipolar cells of the same type whose lower cluster, however, arborizes in the more external sublayers of the inner plexiform layer; g, bipolar cell with a flat cluster of enormous extent; f, another bipolar cell with a giant upper cluster characterized by the rich, irregular arborization formed by the ascending processes; h, oval cells lying outside the outer plexi-form layer; i, amacrine call located within the second sublayer of the inner plexiform layer; j, amacrine cell occupying the third sublayer; m, another amacrine cell whose branches apparently disappear in the third and fourth sublayers. <-

was discovered that in addition to retrograde degeneration in the LGN that is caused by cortical lesions, there is also transneuronal degeneration in the retinal ganglion cell layer after lesion of the cerebral cortex.

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