Electrical neural stimulation and its application to high-resolution retinal prosthesis
- Nervous system enables perception of sensory information, cognition, control of body organs and motor functions by means of signal transmission across the body-wide neural networks. Electrical nature of neural signaling provides an opportunity for control of the signals using external electric field. It enables introduction of information into the diseased neural systems, thereby augmenting and restoring (to some extent) its function. Prosthetic and therapeutic applications of electrical neural stimulation continue to expand. They currently include augmented sensory inputs, such as cochlear and retinal prostheses, treatment of essential tremor and chronic pain with deep brain stimulation, bladder control, and many others. Retinal degenerative diseases lead to blindness due to slow demise of photoreceptors, while other retinal neurons survive to a large extent, which provides an opportunity for reintroduction of information into the visual system by electrical stimulation of the inner retinal neurons. This work describes the dynamics of the extracellular electrical stimulation of spiking neurons and of neural networks, and application of such electro-neural interfaces to retinal prosthesis. Biophysical modeling of the active membrane properties of neurons in external electric field and generation of the action potential was based on Hodgkin-Huxley formalism of ion channel dynamics. Strength-duration relationship calculated for various pulse shapes predicted the existence of the stimulation upper threshold due to reversal of the sodium ionic current at high stimulation strengths. This phenomenon was experimentally confirmed in retinal ganglion cells (RGCs) using the patch clamp recordings. Besides the direct stimulation of RGCs, two types of the network-mediated responses have been identified in the whole-mount retina: originating in the photoreceptors and in the inner retinal neurons. Selectivity of the direct and network-mediated stimulation of RGCs as a function of the electrode location (above, below and inside the retina), geometry (bipolar vs. monopolar), pulse polarity and duration was assessed. These results defined the current configuration of the photovoltaic retinal prosthesis. Each pixel in such implant converts pulsed near-infrared illumination into pulses of electric current flowing through the retina and stimulating the nearby neurons. A computational model describing the optoelectronic properties of such pixels in biological tissue was developed and experimentally verified. Thresholds and selectivity of the network-mediated retinal stimulation have been then measured with photovoltaic arrays. These results provide foundation for further optimization of the photovoltaic retinal prosthesis towards 3-dimensional electro-neural interfaces, to restore high visual acuity and contrast sensitivity in patients blinded by retinal degeneration.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Physics.
|Statement of responsibility
|Submitted to the Department of Physics.
|Ph.D. Stanford University 2014
- © 2014 by David Boinagrov
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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