Mechanisms of Motion Detection in Retinal Neural Network

Abstract Detection of moving objects is a retinal function which is crucial for an animal's survival. Multiple neurons and neural networks in the retina have been identified as critical players in this task, including starburst amacrine cells (SACs) and direction-selective ganglion cells (DSGCs), which sense direction of motion. Recent studies have revealed that several neural networks among bipolar and amacrine cells are involved in direction selectivity. However, the impact of environmental factors on motion sensitivity tuning of these neurons is not well understood. Background scenery affects the gain control and tuning of neurons for object motion detection; however, we have just begun to understand the sensitization and adaptation of those neurons. The long-term objective of the present project is to understand the cellular and molecular mechanisms in the retina for sensing direction of motion. We will conduct patch clamp recordings, two-photon calcium imaging, immunohistochemistry, computational simulation, and behavioral studies to examine the mechanisms underlying direction selectivity. We previously found that cholinergic feedback from SACs to bipolar cells contributes to SAC direction selectivity. We now have evidence that the cholinergic feedback is transferred for a long distance and tune SAC direction selectivity. Therefore, we hypothesize that an incoming object send a signal to bipolar cells through a cholinergic pathway to tune SAC direction selectivity, a form of predictive coding. We propose two Specific Aims to investigate long-distance cholinergic feedback. We will test this hypothesis by recording long-distance cholinergic feedback in bipolar cells (Aim 1), and we will examine the outcome of the long-distance cholinergic feedback in bipolar cell axon terminals, SAC dendrites, and DSGC activity (Aim 2). Visual prediction is an essential feature for motion detection, which would reduce neural signal delays and facilitate the animal reaction. Knowledge gained from the results of this project will shed light on the additional layer of motion detection and visual signal processing in the retina.