Abstract:
Much of the interpretation of our visual world takes place in the retina itself through the actions of specialized neural circuits. Rods and cones, whose distributions and interactions with other retinal neurons have evolved differently among species, form the initiating elements of these circuits. Neurons within the retina, horizontal cells, amacrine cells, bipolar cells, and ganglion cells, extract salient elements from the rod and cone sensory layer using patterns of selective excitatory and inhibitory, often novel, synaptic connections within the retinal synaptic layers. The retina segregates these extracted image elements into parallel output pathways specifying image features and transmits them for further analysis to brain visual centers. The system is adaptive to conditions of illumination, sometimes employing locally diffusing neuromodulators to signal global changes in scene. All this image processing occurs within a photosensitive sheet of neural tissue less than half a millimeter thick. This review previews and highlights the content of Webvision, a tutorial website containing a set of chapters written by experts in the field on the elements of visual-system anatomy and function, focusing on retina, its embryonic development, image processing capabilities, disruptions in disease, prospects for cure, and implications for nervous system research.
About the Authors
Helga Kolb, Ph.D. is the originator and chief editor of Webvision. She was born in London and received postgraduate degrees from Bristol University. Helga has been in eye research since 1961, at first doing electrophysiology at the Institute of Ophthalmology, Moorfields Eye Hospital, and then emigrating to the USA. In John Dowling’s lab at the Wilmer Eye Institute, Johns Hopkins University, along with Brian Boycott, she continued work in anatomy of the retina concentrating on understanding the neurons and wiring of the primate retina. Later at NIH in Bethesda, she collaborated with Peter Gouras and Ralph Nelson on joint physiology and electron microscopy of retinal neurons to understand the connections of cell types involved in light, dark and color pathways in cat and monkey retinas. She joined the faculty at the University of Utah Medical School, Salt Lake City in 1979 and is currently a Professor Emeritus in the Department of Ophthalmology and Visual Science at the John Moran Eye Center.
Ralph Nelson Ph.D. (associate editor) was born in Hartford Connecticut. He received a B.A. in Biophysics from Amherst College and a Ph.D. in Biophysics from Johns Hopkins University. He is currently an NIH Scientist Emeritus at The National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda Maryland. While at Johns Hopkins, he studied ionic mechanisms responsible for light responses of retinal bipolar cells and in his postdoctoral studies at the National Institutes of Health he pioneered the use of intracellular recording for electron-dense staining of retinal neurons in the mammalian retina, a technique that provided insights into the neural circuits for image processing in the inner retina. Helga Kolb and he made major contributions towards the understanding neural pathways that separately process light and dark objects in mammalian retina and the separate neural circuits for nocturnal and diurnal vision. Dr. Nelson currently investigates neural responses in zebrafish retina and the ways in which they are perturbed by genetic mutation.
An American Scientist article on “How the Retina Works” is available here.
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