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1 Vision Science, UC Berkeley, Berkeley, CA, USA
2 Bioengineering, UC Berkeley, Berkeley, CA, USA
* To whom correspondence should be addressed. E-mail: werblin{at}berkeley.edu.
The goal of retinal prosthetic devices is to generate meaningful visual information in patients that have lost outer retinal function. To accomplish this, these devices should generate patterns of ganglion cell activity that closely resemble the spatial and temporal components of those patterns that are normally elicited by light. Here, we have developed a stimulus paradigm that generates precise temporal patterns of activity in retinal ganglion cells including those patterns normally generated by light. Electrical stimulus pulses 
1 ms duration) elicited activity in neurons distal to the ganglion cells; this resulted in ganglion cell spiking that could last as long as 100 ms. But short pulses, less than 0.15 ms elicited only a single spike within 0.7 ms of the leading edge of the pulse. Trains of these short pulses elicited one spike per pulse at frequencies up to 250 Hz. Patterns of short electrical pulses (derived from normal light elicited spike patterns) were delivered to ganglion cells and generated spike patterns that replicated the normal light patterns. Finally, we found that one spike per pulse was elicited over almost a 2.5:1 range of stimulus amplitudes. Thus a common stimulus amplitude could accommodate a 2.5:1 range of activation thresholds, e.g., due to differences arising from cell biophysical properties or from variations in electrode-to-cell distance, arising when a multi-electrode array is placed on the retina. This stimulus paradigm can generate the temporal resolution required for a prosthetic device.
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