Abstract
Purpose :
Regionally and functionally distinct retinal circuits adapt to changes in average light intensity (luminance) to prevent saturation and support a consistent perception of contrast. Our knowledge of photopic (daylight) retinal luminance adaptation in primates comes from studies of peripheral retinal responses to light increments, which have identified two distinct sites of adaptation: cone photoreceptor and downstream circuit adaptation. However, a significant gap in knowledge is how these distinct adaptation mechanisms function in the fovea—the central most region of retina responsible for high-acuity vision where the dominant neural circuitry, the midget pathway, receives input from a single cone and therefore lacks pooling or convergence of cone inputs. Therefore, we tested the role of retinal circuit adaptation in distinct foveal vs peripheral and ON vs OFF retinal circuits.
Methods :
We targeted non-human primate retinal circuits—foveal vs peripheral and ON vs OFF—using single-cell electrophysiology to measure light-evoked electrical responses from primate ganglion cells as well as cone photoreceptors across a range of background luminance.
Results :
Regional comparisons show that unlike in the peripheral retina, foveal ON midget ganglion cells show limited adaptation at dim background luminance. This suggests that cone photoreceptors dominate luminance adaptation in the foveal ON midget pathway at all light levels. ON vs OFF circuit comparisons show peripheral OFF midget ganglion cells demonstrate increased adaptation at the brightest luminance levels tested when compared to peripheral ON midget ganglion cells.
Conclusions :
These results indicate that mechanisms for luminance adaptation in primate foveal vs peripheral and ON vs OFF retinal circuits differ. These differences correlate with changes in retinal circuit convergence between foveal and peripheral circuits as well as the strength of photoreceptor input between light decrements and increments.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.