Receptive Fields of Retinal Ganglion Cells

The intrinsic temporal properties of alpha and beta retinal ganglion cells are equivalent

BACKGROUND

Mammalian retinal ganglion cells have been traditionally classified on the basis of morphological and functional criteria, but as yet little is known about the intrinsic membrane properties of these neurons. This study has investigated these properties by making patch-clamp recordings from morphologically identified ganglion cells in the intact retina.

RESULTS

The whole-cell configuration of the patch-clamp technique was used to assess the temporal tuning characteristics of alpha and beta cells, the two most extensively studied ganglion cell classes. Fourier analysis was used to examine discharge patterns in response to sinusoidal currents of different frequencies (1-50 Hz). With few exceptions, neurons responded in a stereotypic fashion to changes in temporal modulation, with their output initially increasing and then decreasing as a function of stimulus frequency. Moreover, peak responses in both cell classes were obtained at equivalent temporal frequencies. At high stimulus rates, response probability decreased, but the spikes remained phase-locked to the stimulus cycle, thereby enabling populations of cells to convey temporal information. A small number of ganglion cells did not show an appreciable decrease in output as a function of stimulus frequency, but these cells were not confined to either ganglion cell class.

CONCLUSIONS

These findings provide the first evidence that the intrinsic temporal properties of alpha and beta cells are alike. Furthermore, the responses obtained to direct current injections were strikingly similar to those described previously with temporally modulated visual stimuli, suggesting that intrinsic membrane properties may shape the visual responses of alpha and beta cells to a larger degree than has been commonly assumed.

Complicated substructure from simple circularly symmetric Gaussian processes within the centers of goldfish ganglion cell receptive fields

The center of the receptive field of some retinal ganglion cells exhibits an interesting fine structure: the relative amplitudes of responses to onset and responses to offset of a small spot of light varies systematically as the spot is positioned at various places within the center. Although this pattern may appear complicated, a simple model can account for it in detail. The model postulates that the ganglion cell receives input from separate ON and OFF processes within the center of its receptive field. These processes have the form of Gaussian functions and are laterally displaced from each other. These central ON and OFF input processes are not associated with the additional antagonistic surround of the receptive field. The model is examined for various parameters of the input processes. The observed systematic variation in the ratio of offset to onset responses is predicted when the two processes are of nearly equal width (standard deviation of the Gaussians). Receptive fields made of more than two Gaussians produce various patterns, depending on the relative standard deviations of the Gaussians. Oblong fields, reminiscent of those found in visual cortex, may be generated from a relatively small number of circularly symmetric Gaussian processes.