Encoding Visual Features by Parallel Ganglion Cell Initiated Pathways
Photons are sensed by retinal photoreceptors whose matrix-like distribution underlies the transformation of the illumination pattern of the visual scene into a photoreceptor activity pattern in a visuotopic fashion. Activity of neighboring photoreceptors then are compared by secondary bipolar cells to decipher information regarding luminosity- and color-contrast and ultimately sent to retinal ganglion cells, the output neurons of the retina. Bipolar cells achieve this by comparing illumination information received directly from their center receptive field with those come from spatially offset surround receptive field areas mediated by inhibitory, sign-inverting horizontal cells. Retinal ganglion cells sample various bipolar cell subtypes in their dendritic field and utilize collected inputs to generate subtype specific information on luminosity-contrast, color-contrast, object motion, background motion, motion direction, changes in background illumination in a subtype specific manner.
In addition to the excitatory bipolar cell inputs, spatial and temporal features of ganglion cell activation are robustly modified by inhibitory chemical and/or excitatory electrical synaptic inputs provided by inner retinal amacrine cells. Ganglion cells in each subtype cover the retinal surface economically, thus collective information across the population provide a feature pattern and through time a feature movie to the brain. Some of these movies are utilized for image perception, whereas others are sent to accessory visual brain centers to control eye-movement, pupil contraction or circadian entrainment. A large body of information has been revealed in the past decade regarding this field, however much of the details still remain unknown or even enigmatic. This topical issue aims to shed light on many of these unresolved questions, including: (i) the description of neural circuits that serve each ganglion cell subtype to generate their own feature movie; (ii) the estimation of the number of various ganglion cell subtypes that partake in image forming and non-image forming signaling towards the brain; (iii) the description of changes in the inputs, morphology and signaling of retinal ganglion cells when the tissue undergoes disease related degenerative processes; (iv) the comparison of ganglion cell classes with those of the human retina and finally, (v) the practical use of all the above information to establish retina inspired visual algorithms that can be utilized for computer, drone and/or robotic vision.
Journal of Clinical and Experimental Ophthalmology
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