Responses of ganglion cells to repetitive electrical stimulation of the retina

Retinal ganglion cells (RGCs) can be activated electrically either directly or indirectly (via the retinal neural network). Previous studies have shown that RGCs can follow high stimulus rates (>= 200 pulses s(-1)) when directly activated. In the present study, we investigated how well RGCs can follow repetitive stimulation of the neural network. We studied the responses (spike activity) of RGCs in isolated rabbit retina to stimulation with paired pulses applied at different interpulse intervals and trains of pulses applied at different frequencies. We found that the response amplitude of a RGC to a current pulse applied soon (<= 400 ms) after a preceding current pulse is diminished. This depression in response amplitude became greater as the interval between pulses became shorter. At an interpulse interval of 15 ms (shortest tested), the response amplitude to the second current pulse was reduced on average 94%. When a train of ten stimulus pulses was applied, further depression was observed, particularly at high stimulation frequencies. The depression with each successive pulse was relatively moderate compared to the depression to the second pulse. The results of this study have implications for the design of electrical stimulation strategies in a retinal prosthesis.