Motion Processing in Direction Selective Retinal Ganglion Cells through Dynamic Environments

Abstract

Direction selective ganglion cells (DSGCs) signal the presence and direction of motion from the retina to multiple brain areas. Reliably signaling motion is critical through dynamic environments, including contrasts and light levels. This dissertation examines how direction-selective responses are reliably generated across stimulus contrasts, and how populations of DSGCs adapt to changes in light level, spanning moonlight to daylight. In Chapter 2, I describe the development of a functional classification method to identify and classify DSGCs. In Chapter 3, I show how NMDA-dependent synapses improve direction coding in DSGCs at threshold contrasts. In Chapter 4, I describe changes in DSGC responses across light levels, and how these adaptive changes depend on cell types. Chapter 5 focuses on two mechanisms that contribute to this cell type-dependent adaptation: connexin36-mediated electrical coupling and differences in effective GABAergic inhibition. In Chapter 6, I show with a simulation of DSGC activity based on data that this adaptation strategy is beneficial for balancing motion detection and direction estimation at the lower signal-to-noise encountered at night.