Abstract
Abstract: :
Purpose: To characterize the reproducibility and patterning of retinal ganglion cell spike trains elicited by either a natural light stimulus or a simulated postsynaptic current. Methods: We recorded from individual ganglion cells in the isolated, intact, perfused retina of the tiger salamander. The retina was stimulated with a spatially uniform, time-varying light, with intensity values taken from a natural time series (van Hateren 1997). Light-evoked postsynaptic potentials (PSPs) and postsynaptic currents (PSCs) were recorded using the whole-cell patch clamp technique. Light-evoked current responses were then averaged online, and the average current was injected back into the cell. The resulting current-evoked PSPs were recorded under current clamp. Results: 1) Retinal ganglion cells fire with greater temporal precision in response to repeated injections of a current than they do in response to repeated applications of the same natural light stimulus. 2) Firing patterns of different ON-OFF ganglion cells in response to the same natural stimulus are remarkably consistent across experiments—regardless of an individual cell’s latency, overall firing rate, or characteristic firing duration. Taken as a pattern, these conserved spikes represent a sparse code that is reproducible from cell to cell. 3) Current-evoked PSPs exhibit greater membrane potential variability than do light-evoked PSPs. This variability is reduced in the presence of a steady background light. Conclusions: Given the greater precision of current-evoked spike timing, we conclude that the spike generating mechanism of ganglion cells does not limit the reliability of the retina’s response to light. The consistency in the firing pattern of different ON-OFF cells evoked by the same stimulus suggests that the firing pattern is precisely determined by the functional properties of the retinal network, as opposed to the intrinsic properties of individual ganglion cells. The observed suppression of membrane variability by light maintains a reliable ganglion cell membrane potential across repeated trials of the same light stimulus, enabling the precisely patterned retinal response to be faithfully communicated.
Keywords: ganglion cells • electrophysiology: non-clinical • retina: proximal(bipolar, amacrine, and gangli