RETINAL EXCITATION AND INHIBITION FROM DIRECT ELECTRICAL STIMULATION

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Abstract
In rabbits under urethane anesthesia brief electrical stimuli were applied transretinally and their effects measured by the discharge activity of single retinal ganglion cells. A transretinal pulse of .5 msec. duration typically evoked a sequence of 2 to 4 bursts of ganglion cell firing resembling the pattern of light-induced activity. Dual pulses and a.c. stimulation revealed that burst activity is the overt manifestation of a damped oscillation of alternating excitation and inhibition. The fundamental oscillation had a natural period of 30-35 msec. and a damping coefficient which varied between 15 and 40 sec-1. The effects of paired stimuli summated principally in an algebraic fashion. At certain intervals the summation of inhibitory phases rendered dual stimulation ineffective. Various other phenomena of the interactions of two stimuli are described in detail. Single electrical pulses were paired with light flashes and interactions demonstrated resembling those with two electrical stimuli. Steady exposure to light depressed the responsiveness to electrical pulse stimulation in proportion to the logarithm of light intensity. Based upon histological consideration, the network subserving retinal inhibition is discussed with the conclusion that the most probable site of action of the electrical pulse is the proximal end of the visual cells and that the excitatory-inhibitory oscillation is probably induced by interaction between contracting receptor endings.