Retinal Spatiotemporal Patterns And Efficient Information Processing

The retina is the first stage for visual information processing. Photoreceptors transmit the light stimulus into electrical signals which are further processed by retinal circuits. Retinal ganglion cells, the output neurons of retina, send all the visual information to the brain using spikes transmitted through their axons. During information processing, the retina suffers a lot of constraints such as the anatomic bottleneck structure of visual pathway, the noises within neural circuits and the limited metabolic energy etc. Present work is mainly aimed to investigate the spatio- temporal response patterns and efficient aspects of information processing in the retina, employing electrophysiological and theoretical approaches. The main work including three parts: 1) investigating the possible mechanism underlying retinal cone-LHC synapse modification; 2) quantitatively study for retinal information processing during contrast adaptation; 3) the spatiotemporal response patterns of population retinal ganglion cells, given the motion or natural stimuli.The main findings including: 1) postsynaptic [Ca2+]i dependent regulation mechanism acting on AMPA receptors may be responsible for repetitive-red-light-induced response enhancement observed in LHC; 2) during contrast adaptation, the information transmission rates of retinal ganglion cells decreased as well as the firing rates, however, the information content carried by each spike increased significantly compared with pre-adaptation level. Further analysis indicated this kind of bi-directional regulation mechanism for neuronal sensitivity, similar with the observed behavior of retinal ganglion cells during contrast adaptation, can promote the neuron's ability for weak signal detection and processing under background noises; 3) non-direction- selective ganglion cells may also participate in motion information processing in a population coding manner. These neurons represent the stimulation strength by its firing rate, whereas motion information can be reliably read out from their spatiotemoral response patterns. Moreover, for natural movie stimuli, the population ganglion cells show quite sparse spatiotemoral responses.These results clearly indicated the retina processes the visual information in a highly dynamic and efficient manner. Both the adaptation and the population coding operations allow the retina to encode the visual information with remarkably high sensitivity and efficiency, and at the same time, saving the metabolic energy consuming and reducing the number of neurons involved.