Luminance-dependent changes of retinal output: phenomenon and mechanisms
Final Report Abstract
Our retina is continually exposed to changing visual conditions, because we constantly move through a varied environment. Yet, we seem strongly immune to such variability. Partly this is because the retina compensates for some changes in its input, thereby enabling stable signaling to higher visual centers. However, other changes, even simple ones, can lead to altered signaling from the retina to the brain. For example, moderate alteration of ambient brightness (e.g. by wearing sunglasses) can have dramatic effects on the retinal output. Here, we studied the effects of the changing ambient light level on the processing of visual information by the retina. The two photoreceptor classes in the retina, the rods and the cones, underly the astonishing capability of the retina to support vision over such a wide range of intensities. It has long been thought that rods saturate at high (photopic) light levels, and that vision is then exclusively driven by cones. We showed here that this is not the case: rods support vision at all light levels. The certainly become less sensitive at high light levels, but they regain sensitivity over time. What is more, quite counterintuitively, they regain sensitivity faster and more robustly at brighter photopic light levels. Another challenge for the visual system is self-motion of the observer, in particular sudden eye movements (saccades), which lead to jumps in the image flow across the retina. Saccadic suppression is a psychophysical phenomenon that leads to reduced visual sensitivity around the time of those jumps. We showed that saccadic suppression is an inherently visual phenomenon, that is kick-started by visual processing in the retina. Under scotopic (night-vision) conditions, this retina suppression after image motion is substantially weaker than at higher light levels. The retina mostly responds to changes in light intensity; the magnitude of this change is known as contrast. We studied how contrast is encoded by the retina, and we found that light increments and decrements are encoded differently: The spike rate of OFF ganglion cells represents the absolute decrease of light intensity. The spike rate of ON ganglion cells, on the other hand, represents the relative increase of light intensity. This difference of contrast encoding between ON and OFF ganglion cells is preserved across different ambient light levels.
Publications
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(2017) Rods progressively escape saturation to drive visual responses in daylight conditions. Nat Commun. 2017 Nov 27;8(1):1813
Tikidji-Hamburyan A, Reinhard K, Storchi R, Dietter J, Seitter H, Davis KE, Idrees S, Mutter M, Walmsley L, Bedford RA, Ueffing M, Ala-Laurila P, Brown TM, Lucas RJ, Münch TA
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(2019) Evaluation of optogenetic treatments of blindness – development of in-vitro and invivo methods to evaluate the treatment success as well as the characterization of retinal target responses. Dissertation, University Tübingen. Supervision: Münch TA
Mutter M
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Different contrast encoding in ON and OFF visual pathways. bioRxiv 2020
Idrees S, Münch TA
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Suppression without inhibition: A novel mechanism in the retina accounts for saccadic suppression. bioRxiv 2020
Idrees S, Baumann MP, Korympidou MM, Schubert T, Kling A, Franke K, Hafed ZM, Franke F, Münch TA
