A Virtual Electrode through Summation of Time Offset Pulses

Authors: Isaac Cassar, Trevor Davis, Yi-Kai Lo, Wentai Liu

Abstract:

Retinal prostheses have been successful in eliciting visual responses in implanted subjects. As these prostheses progress, one of their major limitations is the need for increased resolution. As an alternative to increasing the number of electrodes, virtual electrodes may be used to increase the effective resolution of current electrode arrays. This paper presents a virtual electrode technique based upon time-offsets between stimuli. Two adjacent electrodes are stimulated with identical pulses with too short of pulse widths to activate a neuron, but one has a time offset of one pulse width. A virtual electrode of twice the pulse width was then shown to appear in the center, with a total width capable of activating a neuron. This can be used in retinal implants by stimulating electrodes with pulse widths short enough to not elicit responses in neurons, but with their combined pulse width adequate to activate a neuron in between them.

Keywords: Electrical stimulation, Neuroprosthesis, Retinal implant, Retinal Prosthesis, Virtual electrode.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1096115

References:

[1] Stone J L, Barlow W E, Humayun M S, Dejuan E and Milam A H. Morphometric analysis of macular photoreceptors and ganglion-cells in retinas with retinitis-pigmentosa Arch. Ophthalmol. Vol. 110 pp. 1634– 9, 1992.
[2] Sekirnjak C, Hulse C, Jepson L H, Hottowy P, Sher A, Dabrowski W, Litke A M and Chichilnisky E J. Loss of responses to visual but not electrical stimulation in ganglion cells of rats with severe photoreceptor degeneration J. Neurophysiol. Vol. 102 pp. 3260–9, 2009.
[3] Humayun M S, Weiland J D, Fujii G Y, Greenberg R, Williamson R, Little J, et al. Visual perception in a blind subject with a chronic microelectronic retinal prosthesis Vis. Res. Vol. 43 pp. 2573–81, 2003.
[4] Yanai D, Weiland J D, Mahadevappa M, Greenberg R J, Fine I and Humayun M S. Visual performance using a retinal prosthesis in three subjects with retinitis pigmentosa Am. J. Ophthalmol. Vol. 143 pp. 820– 7, 2007.
[5] Ahuja A K, Dorn J D, Caspi A, McMahon M J, Dagnelie G, Dacruz L, Stanga P, Humayun M S and Greenberg R J Blind subjects implanted with the Argus II retinal prosthesis are able to improve performance in a spatial-motor task Br. J. Ophthalmol. Vol. 95 pp. 539–43, 2011.
[6] Hecht, Eugene. Optics, 2nd Ed, Addison Wesley, 1987.
[7] McCreery D B, Agnew W F, Yuen T G H and Bullara L Charge density and charge per phase as cofactors in neural injury induced by electrical stimulation IEEE T. Bio-Med. Eng. Vol. 37 pp. 996–1001, 1990.
[8] Weiland JD, Liu W, Humayun MS Retinal Prosthesis. Annu Rev Biomed Eng Vol. 7 pp. 361-401, 2005.
[9] Khalili M G, Lovell N H, Wilke R G, Suaning G J, Dokos S. Performance optimization of current focusing and virtual electrode strategies in retinal implants Comput. Meth. Prog. Biomed. To be published.
[10] Charles T, Choi M, Hsu C H. Conditions for generating virtual channels in cochlear prosthesis systems. Ann. of Biomed. Eng. Vol. 37 pp. 614-24, 2009.
[11] Suzuki S, Humayun M S, Weiland J D, Chen S J, Margalit E, Piyathaisere D V, et al. Comparison of electrical stimulation thresholds in normal and retinal degenerated mouse retina, Jpn J Ophthalmol, Vol. 48 pp. 345–9, 2004.
[12] Lo Y, Chen K, Gad P, Liu W A fully integrated high compliance voltage soc for epi-retinal and neural prostheses IEEE Trans. Biomed. Circuits Sys. Vol. 7 pp. 761–72, 2013
[13] Jensen R J, Rizzo J F, Grumet A E, Edell D J, Wyatt J L Single unit recording following extracellular electrical stimulation of rabbit retinal ganglion bodies. Technical Report 600, MIT Research Laboratory of Electronics, 1996
[14] Rattay F, Aberham M. Modeling axon membranes for functional electrical stimulation IEEE T. Bio-Med. Eng. 40 pp. 1201-1209, 1993.
[15] Coburn B. Neural modeling in electrical stimulation Critic. Rev. Biomed. Eng. Vol. 17 pp. 133-78, 1989