Classical and neoclassical methods of parsing the visual system. (a) Neural network underlying prey capture in anuran amphibians . Anatomical studies from 1969 to 1999 were compiled to show the complex interconnectivity of visual and olfactory inputs, forebrain and midbrain contributions, and motor outputs. The retina is boxed in blue, and retinorecipient regions are boxed in red. Such schemes provide a framework for further study but do not address the pathways' micro-circuitry. A, anterior thalamus; PT, pretectum; OT, optic tectum; R, retina; V, ventral thalamus. Modified from . (b) Scheme showing the major retinofugal connections in the larval zebrafish. Colored circles are stand-ins for diverse cell types, already known or yet to be discovered. The quantities in parentheses are estimates of the number of cell types (data compiled from work on zebrafish and other cyprinids). The retina comprises three cellular layers with five types of photoreceptors (4 cones, 1 rod), at least 11 bipolar cell types, about 70 amacrine cell types , and so on. The number of tectal neuron types is also large. Distinct RGC types (colors) likely have specific roles and connections with ten retinorecipient arborization fields (AF1 to AF9 plus AF10, which is the tectum) in the brain. Some anatomical details (as far as known): the RGCs that are connected to AF7 project a collateral to SO; RGC axons projecting to SAC/SPV in the tectum are routed through AF9. Abbreviations: AC, amacrine cell; AF, arborization field; BC, bipolar cell; GC, ganglion cell; HC, horizontal cell; INL, inner nuclear layer; IPL, inner plexiform layer; OPL, outer plexiform layer; PhR, photoreceptor; PVN, periventricular neuron; SAC, stratum album centrale; SFGS, stratum fibrosum et griseum superficiale; SGC, stratum griseum centrale; SIN, superficial interneuron; SO, stratum opticum; SPV, stratum periventriculare.
Nevin et al. BMC Biology 2010 8:126 doi:10.1186/1741-7007-8-126