A Method for Generating Precise Temporal Patterns of Retinal Spiking Using Prosthetic Stimulation

Abstract

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 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 (> or =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. However, short pulses, <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 < or =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., caused by differences arising from cell biophysical properties or from variations in electrode-to-cell distance arising when a multielectrode array is placed on the retina. This stimulus paradigm can generate the temporal resolution required for a prosthetic device.

Optimization of Stimulation Parameters for Targeted Activation of Multiple Neurons Using Closed-Loop Search Methods

“…The model constructed for N3 was a set of two sigmoids (described in Figure 4D) and for N4 was zero because the slice did not cross the set of SD curves for that neuron. The maximum of the objective function, combining all five neuronal activation models according to (7) was found at PT3 (870 µs, 9.5 µA). The fourth search was horizontal, parallel to the second search, and the maximum of the function was found at PT4 (990 µs, 9.5 µA).…”

“…The prosthesis field is expansive, including peripheral and cortical prostheses, with applications including restoration of lost motor and sensory function in artificial limbs; cochlear prostheses for restoring audition [5,6]; retinal prostheses for restoring vision [7][8][9]; and cortical prostheses for inducing sensory percepts and reading motor intent directly from the brain [10][11][12][13][14][15][16]. An effective prosthesis must encode a variety of unique stimuli.…”

A Treatise of the Physical Aspects of Phosphenes and Single-Cell Selectivity in Retinal Stimulation

“…As such, electrolysis of water, the formation of corrosion [41] and excessive tissue heating that leads to significant damage to various cellular functions [42] must be avoided. A Matlab script organized the extracted data of voltage across the electrodes and current delivered by the electrode and performed several tasks to obtain the heat dissipated at the device and charge density on the electrode.…”

“…Decreasing electrode dimensions generate higher resolution patterns of prosthetic-elicited activity that are closer to lightelicited patterns [41]. The prosthetic devices developed by Mahadevappa et al, [10], Rizzo et al, [12], Klauke et al, [13] Eger et al, [14] and Humayun et al, [16] used big-sized electrode diametersof 500, 200 and 100 µm, respectively.…”

“…Reducing electrode dimensions will generate small activation areas that could stimulate a single cell. However, thiscould cause a breakdown of the electrode and adverse tissue reactions due to a high charge density demand [41].…”