Cat Retinal Ganglion Cell Responses to Changing Light Intensities: Sinusoidal Modulation in the Time Domain

Abstract

Abstract Action potentials were recorded from single axons of retinal ganglion cells in adult lightly anesthetized, paralyzed cats (intact eye). A small, sinusoidally time modulated stimulus was located in the most responsive portion of the receptive field center. The mean discharge frequency was monitored on a counter during the experiment and the responses over extended periods of time were recorded on tape and later averaged. Most of the cells were outside area centralis. A series of experiments showed that doses of muscle paralyzing agents several times larger than those commonly used in cat retinal ganglion cell experiments were needed for unfailing long‐lasting eye immobilization. In a second series of experiments the mean discharge frequency of the cell, the peak‐peak amplitude of the averaged response and the stimulus‐response phase difference were studied as: (a) a function of modulation depth at constant frequency, (b) a function of stimulus frequency at constant depth of modulation. Only two of 31 cells exhibited (up to 40 per cent modulation) a mean discharge frequency independent of modulation depth, a response amplitude reasonably proportional to modulation depth, an almost constant stimulus‐response phase difference and an averaged response whose shape was almost sinusoidal. The remaining cells failed to fulfill at least one of these requirements for linearity. For 6 cells modulation sensitivity curves were determined and found to have the same general shape as those subjectively determined in humans.