Visual Encoding in the Human Retina : human ganglion cell physiology and comparison to other species

Abstract

Retinal information processing has been characterized in many animal models. Surprisingly, similar systematic measurements have never been performed in human retina. Non-human primate research often focuses on a few, most abundant ganglion cell types, which led to the impression that retinal image processing is less rich in primates than in other mammals. I thus investigated the retinal computations in human retina, and compared it to retinal processing in mouse and pig, as well as to previous publications on non-human primate vision. Analysis of multi-electrode array recordings of mid-peripheral human retina revealed that visual processing is richer than suggested by current literature on primate retina. Human ganglion cells encoded a broad range of speeds, spatial periods, and temporal frequencies. For the first time, ON-OFF type responses have been described in the human retina. Further, I found potential candidates for a Y-like pathway in human retina. I characterized ganglion cells with distance-invariant encoding in both human and pig retina – a response behavior which so far has not been described. I found that visual encoding in human and pig retina has many similarities while there were more differences between human and mouse visual processing. In general, human ganglion cells preferred higher speeds and were tuned to higher temporal frequencies than in mouse. For scientific questions related to very specific circuit behaviors, the porcine retina might thus be a better model than the mouse. In this thesis I do not only discuss the measured retinal properties in humans and other species, but also elaborate on the availability of human retina and methodological possibilities to investigate this tissue. Further, I talk about difficulties with the analysis of high-throughput electrophysiological data and provide solutions. I conclude that donated human retina is a valuable tool for in-vitro physiology experiments. In the future, such tissue might be used for testing of short-term effects of pharmaceuticals and for the evaluation of novel treatment methods for visual impairment.