Figure 9.

Direction-selective responses of RGCs persist in old retina. A, B, Responses of an old BD-RGC (A) and an old J-RGC (B) to flashing spots as a function of the spot radius. C, D, Response of an old BD-RGC (C) and an old J-RGC (D) to small bars moving across their receptive field centers in eight different directions. Plots indicate spikes fired for each direction. E, F, Polar summary of the preferred directions of old BD-RGCs (E) and J-RGCs (F) recorded from well oriented retina. For J-RGCs results are shown in relationship to their dendritic arbor asymmetry (arrowhead). G, Direction selectivity (DS) index for old and young BD- and J-RGCs calculated as described previously (Kim et al., 2008). The DS index of W3-RGCs, a nondirection selective type, is replotted from Kim et al. (2010) for comparison. N = 22, 6, 16, 12 and 11 for young BD-, old BD-, young J-, old J-, and W3-RGCs, respectively. Error bars indicate the SEM. H, Variety of visual responses of RGCs in an aged retina to a flashing spot of optimal size at the receptive field center. Background shading indicates periods when light was off. Each panel is a raster graph of firing from one neuron, and each row is a repeat of the same stimulus. Tick marks represent action potentials. From top to bottom, RGCs are classified as ON transient, ON sustained, ON-OFF, OFF sustained, and OFF transient. I, Responses of RGCs in an aged retina to a flashing spot as a function of the spot radius. All but one of the cells tested showed surround inhibition as indicated by a decrease in the firing rate as the spot radius increased.