The Spatiotemporal Characteristics Of The Chicken Retinal Ganglion Cells' Population Activities In Response To Natural Stimuli

The first stage of the visual information processing occurs in the retina. The photoreceptors absorb photons from the visual field, and signal the light information through changes in their membrane potentials. These signals are further transmitted along the retinal circuit to the output neurons, retinal ganglion cells and make their way to the central visual system in the form of action potentials (spikes). Nearly all the visual experiences happen in natural environment, thus it has been paid more and more attention to investigate the visual information processing using natural stimuli. The information processing in the retina is subject to several restrictions such as the anatomic bottleneck structure of the retina in the visual pathway and the limited metabolic energy. The aim of this investigation is getting to know how the retinal ganglion cells process and encode the natural visual stimuli effectively under such constraints. In the present work, the multi-neuronal activities of the chick retinal ganglion cells in response to time-varying natural images (movies) as well as pseudorandom white-noise checker-board flickering sequence (control) were recorded using multi-electrode recording technique. The statistical distributions of the population retinal ganglion cells'spikes in temporal (over the duration of stimulation) and spatial (across the population neurons), the underlying firing patterns and dynamic grouping of activated neurons in synchronization, were analyzed and investigated.The main findings include three parts: 1) In response to the natural stimuli, the individual single retinal ganglion cell's firing activities over the duration of the stimulation and the multi-neuronal instantaneous activities at the same moment both show more obvious super-Gaussian distribution, which is related to sparse coding of the neurons, than those during stimulation of pseudorandom white-noise checker-board flickering sequence. 2) Further analysis of the experimental data shows that it is the action potentials fired in"burst"form of individual single neurons and synchronized activities of neurons in group that contribute mainly to the sparse representation of the population retinal ganglion cells. These results suggest that in response to natural stimuli, individual neuron fires at a low rate to save metabolic energy, while the dynamically grouped small subsets of neurons are activated with adjacent neurons firing concertedly and individual single neurons fire in"burst"form occasionally to transmit information to the postsynaptic neurons efficiently. 3) Multi-dimensional data analysis based on MSDD (a measurement based on sub-sequence distribution discrepancy) was applied to the spike trains of population retinal ganglion cell during different time periods of the stimulation and the results show that the neurons fried synchronously in dynamic groups over the duration of natural stimulation. Furthermore, an information-theoretic algorithm based on entropy analysis was applied to identify the synchronized neuronal groups of the population RGCs based on the complete spike trains over stimulation. The results show that the synchronized firings in RGCs are more extensive and diverse and may account for more effective information processing in representing the natural visual environment.These results indicate that the retina processes the natural visual information in a highly dynamic and efficient manner through the spatiotemporal firing patterns of the population ganglion cells, which can reduce the number of neurons involved, save the metabolic energy consuming, improve the efficacy of the information transmission and enhance capabilities of the ganglion cells'information reorganization and processing.