Analysis of retinal information processing with multi-electrode recordings

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To analyze the visual information processing in the vertebrate retina, light-induced spike discharges of retinal ganglion cells were recorded extracellularly using a multi-electrode array. The planar electrode array was fabricated by the following methods. A sputtered film of the transparent conductor indium thin oxide (ITO) was patterned on a silica glass wafer by photolithography, using wet etching in HCl. A insulating layr of Al_2O_3 was then applied by evaporation to the whole substrate, but lifted off at the tips of the ITO electrodes by photolithographic patterning. The exposed electrode tips were platinized by electrolytic deposition. A piece of retina was isolated in darkness from a frog, and was mounted on the multi-electrode array. Light stimuli were projected from a computer monitor on the retinal photoreceptor layr. Patterns consisted of a random pixel pattern with independently modulated square fields or a single uniform field, the intensity of which was modulated sinusoidally in the temporal domain. Data were aquired from ganglion cells, which responded phasically to dimming stimuli (dimming cells). Spatio-temporal receptive fields were obtained by analyzing the correlations between each spike discharge and the preceded random pixel pattern. Light adaptation changed their temporal property but not their spatial property. Auto-and cross-correlation analyzes were carried out in spike discharges evoked by a sinusoidally modulated uniform field. The results suggested that dimming cells receive a common input from spiking neurons with large receptive field, which seemed to be amacrine cells.