Bio

Education & Certifications


  • B.S., Stanford University, Biology with Honors in Neurobiology (2018)
  • Minor, Stanford University, Chemistry (2018)
  • Minor, Stanford University, Classics - Classical Studies (2018)

Publications

All Publications


  • Epiretinal stimulation with local returns enhances selectivity at cellular resolution. Journal of neural engineering Fan, V. H., Grosberg, L. E., Madugula, S. S., Hottowy, P., Dabrowski, W., Sher, A., Litke, A. M., Chichilnisky, E. J. 2018

    Abstract

    OBJECTIVE: Epiretinal prostheses are designed to restore vision in people blinded by photoreceptor degenerative diseases, by directly activating retinal ganglion cells (RGCs) using an electrode array implanted on the retina. In present-day clinical devices, current spread from the stimulating electrode to a distant return electrode often results in the activation of many cells, potentially limiting the quality of artificial vision. In the laboratory, epiretinal activation of RGCs with cellular resolution has been demonstrated with small electrodes, but distant returns may still cause undesirable current spread. Here, the ability of local return stimulation to improve the selective activation of RGCs at cellular resolution was evaluated. Approach: A custom multi-electrode array (512 electrodes, 10 mum diameter, 60 mum pitch) was used to simultaneously stimulate and record from RGCs in isolated primate retina. Stimulation near the RGC soma with a single electrode and a distant return was compared to stimulation in which the return was provided by six neighboring electrodes. Main Results: Local return stimulation enhanced the capability to activate cells near the central electrode (<30 m) while avoiding cells farther away (>30 m). This resulted in an improved ability to selectively activate ON and OFF cells, including cells encoding immediately adjacent regions in the visual field. Significance: These results suggest that a device that restricts the electric field through local returns could optimize activation of neurons at cellular resolution, improving the quality of artificial vision.

    View details for PubMedID 30523958

  • Optimizing Selectivity of Epiretinal Stimulation using Local Returns Fan, V., Grosberg, L. E., Madugula, S., Hottowy, P., Dabrowski, W., Sher, A., Litke, A. M., Chichilnisky, E. J. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2017
  • Activation of ganglion cells and axon bundles using epiretinal electrical stimulation. Journal of neurophysiology Grosberg, L. E., Ganesan, K., Goetz, G. A., Madugula, S. S., Bhaskhar, N., Fan, V., Li, P., Hottowy, P., Dabrowski, W., Sher, A., Litke, A. M., Mitra, S., Chichilnisky, E. J. 2017: jn 00750 2016-?

    Abstract

    Epiretinal prostheses for treating blindness activate axon bundles, causing large, arc-shaped visual percepts that limit the quality of artificial vision. Improving the function of epiretinal prostheses therefore requires understanding and avoiding axon bundle activation. This paper introduces a method to detect axon bundle activation based on its electrical signature, and uses the method to test whether epiretinal stimulation can directly elicit spikes in individual retinal ganglion cells without activating nearby axon bundles. Combined electrical stimulation and recording from isolated primate retina were performed using a custom multi-electrode system (512 electrodes, 10 ?m diameter, 60 ?m pitch). Axon bundle signals were identified by their bi-directional propagation, speed, and increasing amplitude as a function of stimulation current. The threshold for bundle activation varied across electrodes and retinas, and was in the same range as the threshold for activating retinal ganglion cells near their somas. In the peripheral retina, 45% of electrodes that activated individual ganglion cells (17% of all electrodes) did so without activating bundles. This permitted selective activation of 21% of recorded ganglion cells (7% of all ganglion cells) over the array. In the central retina, 75% of electrodes that activated individual ganglion cells (16% of all electrodes) did so without activating bundles. The ability to selectively activate a subset of retinal ganglion cells without axon bundles suggests a possible novel architecture for future epiretinal prostheses.

    View details for DOI 10.1152/jn.00750.2016

    View details for PubMedID 28566464

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