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J. S. George, X.-C. Yao; Retinal Responses to Light and Electrical Stimulation Disclosed by High Resolution Dynamic Optical Imaging. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2570.
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© ARVO (1962-2015); The Authors (2016-present)
High resolution imaging of transient intrinsic optical changes tightly coupled to neural activity allows investigation of dynamic visual processing within the retina, and characterization of the consequences of electrical stimulation. Here we report initial studies of the optical responses evoked by light and electrical stimulation of isolated frog retina.
Frogs (rana pipiens) were sacrificed, eyes were removed, and retinas were isolated under dim red illumination. Retinas were transferred to recording chamber incorporating a multi-electrode array. Optical recording employed NIR illumination (750-950 nm) in transmitted light, darkfield or cross-polarized configurations. Physiological stimulation employed a white LED or electrical stimulation from the recording array or by a separate wire electrode. Optical recording employed a high resolution CCD camera operated at high frame rates (>100 fps). An average prestimulus baseline image was subtracted from each image in the sequence, and difference images were divided by the original images (dI/I).
We imaged dynamic optical responses closely tracking electrophysiological activity in the outer retina. CCD image sequences show evidence of multiple response components with both negative- and positive-going signals with different time courses and consistent spatial organization, initially limited to the region activated by the flash. Because of the close juxtaposition of responses of opposite polarity, high-resolution imaging disclosed larger fractional responses in individual pixels, in some cases exceeding 10%. Spatial and temporal structure in the image sequences indicates that we captured images of neurophysiological activation in large populations of individual neurons in single passes. Image sequences of responses to light flashes showed evidence of lateral processing, including enhancement of responses at the perimeter of the stimulated region. Electrical simulation elicited fast activation in the outer retina which was most pronounced near the perimeter of the relatively large stimulating electrodes.
We have developed methods for high resolution dynamic optical imaging of neural activation in the isolated retina based on fast intrinsic light scattering changes. These methods have been used to investigate the physiological response of the retina to light as well as the response to electrical stimulation. Both types of measurements have implications for the design of optimal retinal prosthetic devices.
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