Abstract
Purpose :
The strong temporal variations characteristic of natural visual inputs pose considerable challenges for our understanding of retinal function. Specifically, the large changes in luminance produced by eye movements require strong and rapid adaptation to reliably encode subtle changes in input while avoiding saturation. Such adaptation in turn relies on multiple circuit mechanisms. We know a good deal about how adaptation in the photoreceptors and post-photoreceptor retinal circuits operates for slow changes in luminance—e.g. those encountered as the sun rises or sets. We know much less about their importance for encoding the large and rapid changes encountered as gaze shifts within a single visual scene. Here we focus on the contribution of the cones themselves to this essential visual function.
Methods :
We characterized responses of primate photoreceptors and ganglion cells to inputs that capture the temporal variations characteristic of natural vision. We obtained retinas through the Tissue Distribution Program of the National Primate Research Center at the University of Washington. We then used patch clamp techniques to record responses of cones and ganglion cells. We used these responses as the basis of models that predicted ganglion cell responses based on either linear or adapting cone responses.
Results :
Both cones and ganglion cells adapt strongly and rapidly to naturalistic inputs. Ganglion cell responses were better predicted by models that incorporate adaptation in the cones than models that assumed linear cone responses. The accuracy of the predictions of such models, however, was considerably poorer than predictions of responses to simpler inputs such as gaussian noise. This comparison highlighted the importance of adaptational mechanisms downstream of the cones.
Conclusions :
Responses to complex stimuli such as natural visual inputs are shaped by multiple circuit mechanisms acting collectively. The work here begins to identify the importance of adaptation in the photoreceptors to the ability of the retina to maintain sensitivity during rapid and large changes in input. Future work will focus on mechanisms within the retinal circuitry and the ganglion cells themselves.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.