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G. Spor, A. Molnar, F. Werblin; Amacrine Cell Inhibition Refines the Spatio–Temporal Filtering Properties of Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2675.
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© ARVO (1962-2015); The Authors (2016-present)
There are 10–12 different populations of retinal ganglion cells (RGCs) in the mammalian retina; each can be described as a spatio–temporal filter that passes a specific range of spatial and temporal frequencies. We are interested in how the amacrine cell inhibitory networks of the retina refine the filtering properties of RGCs by shaping and restricting the bands of spatial and temporal frequencies to which they respond.
RGCs were loose–patched to record spike trains in response to visual stimuli in the flat–mounted rabbit retina. Stimuli consisted of drifting gratings with temporal frequencies ranging from 0.5 to 7.5Hz and spatial frequencies ranging from 1 to 20 cycles/mm. 10µM Strychnine and 100µM Picrotoxin were used to block the glycinergic and GABAergic components of inhibition, respectively.
Under control conditions, each class of ganglion cells responded over a preferential range of spatial and temporal frequencies. For example, Local Edge Detectors responded maximally to stimuli with a spatial wavelength (SW) of approximately 200 µm drifting at 0.5 Hz, whereas Off Alpha cells preferred stimuli with a SW of 1 mm drifting at 7.5 Hz. The spatial and temporal bandwidths of both of these cell types were approximately 1 octave. The introduction of Strychnine (a glycine receptor antagonist) tended to broaden cells' spatial and temporal bandwidths while leaving in place the position (in frequency space) of the stimuli to which they responded most strongly. Picrotoxin (a GABAA and GABAC receptor antagonist) tended to shift the cells' tuning to lower spatial and temporal frequencies. A notable exception to these findings are the off alpha cells that respond more strongly to higher temporal frequencies in the presence of strychnine.
GABAergic inhibition suppresses wide–field and sustained responses resulting in cells that are tuned to higher spatial and temporal frequencies. Glycinergic inhibition acts to improve the selectivity of cells, restricting them to specific ranges of spatial and temporal frequencies. These inhibitory systems likely reduce the overlap in space and time with which the different classes of RGCs represent the visual world.
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