Photovoltaic Pixels for Neural Stimulation: Circuit Models and Performance.

Photovoltaic conversion of pulsed light into pulsed electric current enables optically-activated neural stimulation with miniature wireless implants. In photovoltaic retinal prostheses, patterns of near-infrared light projected from video goggles onto subretinal arrays of photovoltaic pixels are converted into patterns of current to stimulate the inner retinal neurons. We describe a model of these devices and evaluate the performance of photovoltaic circuits, including the electrode-electrolyte interface.

Selectivity of direct and network-mediated stimulation of the retinal ganglion cells with epi-, sub- and intraretinal electrodes.

Objective: Intra-retinal placement of stimulating electrodes can provide close and stable proximity to target neurons. We assessed improvement in stimulation thresholds and selectivity of the direct and network-mediated retinal stimulation with intraretinal electrodes, compared to epiretinal and subretinal placements.

Approach: Stimulation thresholds of the retinal ganglion cells (RGCs) in wild-type rat retina were measured using the patch-clamp technique.

Upper threshold of extracellular neural stimulation.

It is well known that spiking neurons can produce action potentials in response to extracellular stimulation above certain threshold. It is widely assumed that there is no upper limit to somatic stimulation, except for cellular or electrode damage. Here we demonstrate that there is an upper stimulation threshold, above which no action potential can be elicited, and it is below the threshold of cellular damage.

Strength-duration relationship for extracellular neural stimulation: numerical and analytical models.

The strength-duration relationship for extracellular stimulation is often assumed to be similar to the classical intracellular stimulation model, with a slope asymptotically approaching 1/τ at pulse durations shorter than chronaxy. We modeled extracellular neural stimulation numerically and analytically for several cell shapes and types of active membrane properties. The strength-duration relationship was found to differ significantly from classical intracellular models.