Characteristics Of Receptive Field Of Bullfrog's Retinal Ganglion Cells

Retina encodes the visual stimulus by converting the light signals into the spike trains of ganglion cells. The dissertation studies the relationship between the receptive field (RF) encoded by each single retinal ganglion cell's firing activity (single-cell-RF) and the RF encoded by the synchronized firing activity of all the ganglion cells (GC) in the group (group-RF), as well as their dynamic characteristics during the period of contrast adaptation.The main contents include two parts: (1) The firing activities of the bullfrog retinal ganglion cells during response to the pseudo-random checkerboard stimulus were recorded in vitro by the multi-electrode recording technology. Based on the firing activities of the GCs recorded, the synchronous GC groups were identified by a data compression algorithm, which compresses the entropy of the spike trains in the maximal extent. We investigated the relationship between the RF encoded by the synchronized firing activity of all the GCs in the group and the RF encoded by each single GC's firing activity. The results revealed that for all the GC groups, about 80% of group-RF sizes were smaller than the mean size of single-cell-RFs in the same groups and about 60% of group-RF sizes were smaller than any single-cell-RF size in the same groups, which indicated that the spatial information encoded by most of the synchronized activities of the GC groups is more precise. (2) The firing activities of GCs have the property of contrast adaptation during response to the checkerboard stimulus. We investigated the dynamic characteristics of single-cell-RF, and the results revealed that about 70% of single-cell-RF sizes were reduced during the late period of adaptation. We chose the GC groups with group-RF size smaller than any single-cell-RF size in the same groups to investigate the dynamics of group-RF during the early and late period of contrast adaptation. The results illustrated that 85% of group-RF sizes of the GC groups were reduced during the late period of adaptation. The declining of the firing rate during the contrast adaptation is helpful to save energy, but the preciseness of single-cell-RF and group-RF is enhanced instead of weakened during the late period of contrast adaptation, which reflects the efficient encoding mechanism of retina.