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Vilkhu RS, Vasireddy PK, Kish KE, Gogliettino AR, Lotlikar A, Hottowy P, Dabrowski W, Sher A, Litke AM, Mitra S, Chichilnisky EJ. Understanding responses to multi-electrode epiretinal stimulation using a biophysical model. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.08.20.608829. [PMID: 39229196 PMCID: PMC11370456 DOI: 10.1101/2024.08.20.608829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2024]
Abstract
Objective Neural interfaces are designed to evoke specific patterns of electrical activity in populations of neurons by stimulating with many electrodes. However, currents passed simultaneously through multiple electrodes often combine nonlinearly to drive neural responses, making evoked responses difficult to predict and control. This response nonlinearity could arise from the interaction of many excitable sites in each cell, any of which can produce a spike. However, this multi-site activation hypothesis is difficult to verify experimentally. Approach We developed a biophysical model to study retinal ganglion cell (RGC) responses to multi-electrode stimulation and validated it using data collected from ex vivo preparations of the macaque retina using a microelectrode array (512 electrodes; 30µm pitch; 10µm diameter). Results First, the model was validated by reproducing essential empirical findings from single-electrode stimulation and recording, including spike waveforms over the electrode array and sigmoidal responses to injected current. Then, stimulation with two electrodes was modeled to test how the positioning of the electrodes relative to the cell affected the degree of response nonlinearity. Currents passed through pairs of electrodes positioned near the cell body or far from the axon (>40 µm) exhibited linear summation. Currents passed through pairs of electrodes close to the axon summed linearly when their locations along the axon were similar, and nonlinearly otherwise. Over a range of electrode placements, several distinct, localized spike initiation sites were observed, and the number of these sites covaried with the degree of response nonlinearity. Similar trends were observed for three-electrode stimuli. All of these trends were consistent with experimental observations. Significance These findings support the multi-site activation hypothesis for nonlinear activation of neurons, providing a biophysical interpretation of previous experimental results and potentially enabling more efficient use of multi-electrode stimuli in future neural implants.
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Son Y, Chen ZC, Roh H, Lee BC, Im M. Effects on Retinal Stimulation of the Geometry and the Insertion Location of Penetrating Electrodes. IEEE Trans Neural Syst Rehabil Eng 2023; 31:3803-3812. [PMID: 37729573 DOI: 10.1109/tnsre.2023.3317496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/22/2023]
Abstract
Retinal implants have been developed and implanted to restore vision from outer retinal degeneration, but their performance is still limited due to the poor spatial resolution. To improve the localization of stimulation, microelectrodes in various three-dimensional (3D) shapes have been investigated. In particular, computational simulation is crucial for optimizing the performance of a novel microelectrode design before actual fabrication. However, most previous studies have assumed a uniform conductivity for the entire retina without testing the effect of electrodes placement in different layers. In this study, we used the finite element method to simulate electric fields created by 3D microelectrodes of three different designs in a retina model with a stratified conductivity profile. The three electrode designs included two conventional shapes - a conical electrode (CE) and a pillar electrode (PE); we also proposed a novel structure of pillar electrode with an insulating wall (PEIW). A quantitative comparison of these designs shows the PEIW generates a stronger and more confined electric field with the same current injection, which is preferred for high-resolution retinal prostheses. Moreover, our results demonstrate both the magnitude and the shape of potential distribution generated by a penetrating electrode depend not only on the geometry, but also substantially on the insertion depth of the electrode. Although epiretinal insertions are mainly discussed, we also compared results for subretinal insertions. The results provide valuable insights for improving the spatial resolution of retinal implants using 3D penetrating microelectrodes and highlight the importance of considering the heterogeneity of conductivities in the retina.
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Yang M, Wang J, Li S, Wang K, Yue W, Liu C. Adaptive closed-loop paradigm of electrophysiology for neuron models. Neural Netw 2023; 165:406-419. [PMID: 37329784 DOI: 10.1016/j.neunet.2023.05.050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Revised: 12/15/2022] [Accepted: 05/27/2023] [Indexed: 06/19/2023]
Abstract
The traditional electrophysiological experiments based on an open-loop paradigm are relatively complicated and limited when facing an individual neuron with uncertain nonlinear factors. Emerging neural technologies enable tremendous growth in experimental data leading to the curse of high-dimensional data, which obstructs the mechanism exploration of spiking activities in the neurons. In this work, we propose an adaptive closed-loop electrophysiology simulation experimental paradigm based on a Radial Basis Function neural network and a highly nonlinear unscented Kalman filter. On account of the complex nonlinear dynamic characteristics of the real neurons, the proposed simulation experimental paradigm could fit the unknown neuron models with different channel parameters and different structures (i.e. single or multiple compartments), and further compute the injected stimulus in time according to the arbitrary desired spiking activities of the neurons. However, the hidden electrophysiological states of the neurons are difficult to be measured directly. Thus, an extra Unscented Kalman filter modular is incorporated in the closed-loop electrophysiology experimental paradigm. The numerical results and theoretical analyses demonstrate that the proposed adaptive closed-loop electrophysiology simulation experimental paradigm achieves desired spiking activities arbitrarily and the hidden dynamics of the neurons are visualized by the unscented Kalman filter modular. The proposed adaptive closed-loop simulation experimental paradigm can avoid the inefficiency of data at increasingly greater scales and enhance the scalability of electrophysiological experiments, thus speeding up the discovery cycle on neuroscience.
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Affiliation(s)
- Ming Yang
- School of Electrical and Information Engineering, Tianjin University, Tianjin, China
| | - Jiang Wang
- School of Electrical and Information Engineering, Tianjin University, Tianjin, China
| | - Shanshan Li
- School of Electrical and Automation Engineering, Tianjin University of Technology and Education, Tianjin, China
| | - Kuanchuan Wang
- School of Electrical and Information Engineering, Tianjin University, Tianjin, China
| | - Wei Yue
- Tianjin Key Laboratory of Cerebral Vascular and Neurodegenerative Diseases, Tianjin Huanhu Hospital, Tianjin, China
| | - Chen Liu
- School of Electrical and Information Engineering, Tianjin University, Tianjin, China.
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Xu A, Beyeler M. Retinal ganglion cells undergo cell type-specific functional changes in a computational model of cone-mediated retinal degeneration. Front Neurosci 2023; 17:1147729. [PMID: 37274203 PMCID: PMC10233015 DOI: 10.3389/fnins.2023.1147729] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 05/02/2023] [Indexed: 06/06/2023] Open
Abstract
Introduction Understanding the retina in health and disease is a key issue for neuroscience and neuroengineering applications such as retinal prostheses. During degeneration, the retinal network undergoes complex and multi-stage neuroanatomical alterations, which drastically impact the retinal ganglion cell (RGC) response and are of clinical importance. Here we present a biophysically detailed in silico model of the cone pathway in the retina that simulates the network-level response to both light and electrical stimulation. Methods The model included 11, 138 cells belonging to nine different cell types (cone photoreceptors, horizontal cells, ON/OFF bipolar cells, ON/OFF amacrine cells, and ON/OFF ganglion cells) confined to a 300 × 300 × 210μm patch of the parafoveal retina. After verifying that the model reproduced seminal findings about the light response of retinal ganglion cells (RGCs), we systematically introduced anatomical and neurophysiological changes (e.g., reduced light sensitivity of photoreceptor, cell death, cell migration) to the network and studied their effect on network activity. Results The model was not only able to reproduce common findings about RGC activity in the degenerated retina, such as hyperactivity and increased electrical thresholds, but also offers testable predictions about the underlying neuroanatomical mechanisms. Discussion Overall, our findings demonstrate how biophysical changes typified by cone-mediated retinal degeneration may impact retinal responses to light and electrical stimulation. These insights may further our understanding of retinal processing and inform the design of retinal prostheses.
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Affiliation(s)
- Aiwen Xu
- Department of Computer Science, University of California, California, Santa Barbara, CA, United States
| | - Michael Beyeler
- Department of Computer Science, University of California, California, Santa Barbara, CA, United States
- Department of Psychological & Brain Sciences, University of California, California, Santa Barbara, CA, United States
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Halgren AS, Siegel Z, Golden R, Bazhenov M. Multielectrode Cortical Stimulation Selectively Induces Unidirectional Wave Propagation of Excitatory Neuronal Activity in Biophysical Neural Model. J Neurosci 2023; 43:2482-2496. [PMID: 36849415 PMCID: PMC10082457 DOI: 10.1523/jneurosci.1784-21.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 12/27/2022] [Accepted: 01/13/2023] [Indexed: 03/01/2023] Open
Abstract
Cortical stimulation is emerging as an experimental tool in basic research and a promising therapy for a range of neuropsychiatric conditions. As multielectrode arrays enter clinical practice, the possibility of using spatiotemporal patterns of electrical stimulation to induce desired physiological patterns has become theoretically possible, but in practice can only be implemented by trial-and-error because of a lack of predictive models. Experimental evidence increasingly establishes traveling waves as fundamental to cortical information-processing, but we lack an understanding of how to control wave properties despite rapidly improving technologies. This study uses a hybrid biophysical-anatomical and neural-computational model to predict and understand how a simple pattern of cortical surface stimulation could induce directional traveling waves via asymmetric activation of inhibitory interneurons. We found that pyramidal cells and basket cells are highly activated by the anodal electrode and minimally activated by the cathodal electrodes, while Martinotti cells are moderately activated by both electrodes but exhibit a slight preference for cathodal stimulation. Network model simulations found that this asymmetrical activation results in a traveling wave in superficial excitatory cells that propagates unidirectionally away from the electrode array. Our study reveals how asymmetric electrical stimulation can easily facilitate traveling waves by relying on two distinct types of inhibitory interneuron activity to shape and sustain the spatiotemporal dynamics of endogenous local circuit mechanisms.SIGNIFICANCE STATEMENT Electrical brain stimulation is becoming increasingly useful to probe the workings of brain and to treat a variety of neuropsychiatric disorders. However, stimulation is currently performed in a trial-and-error fashion as there are no methods to predict how different electrode arrangements and stimulation paradigms will affect brain functioning. In this study, we demonstrate a hybrid modeling approach, which makes experimentally testable predictions that bridge the gap between the microscale effects of multielectrode stimulation and the resultant circuit dynamics at the mesoscale. Our results show how custom stimulation paradigms can induce predictable, persistent changes in brain activity, which has the potential to restore normal brain function and become a powerful therapy for neurological and psychiatric conditions.
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Affiliation(s)
- Alma S Halgren
- Department of Medicine, University of California - San Diego, La Jolla, California 92093-7374
- Department of Integrative Biology, University of California - Berkeley, Berkeley, California 94720
| | - Zarek Siegel
- Department of Medicine, University of California - San Diego, La Jolla, California 92093-7374
- Neurosciences Graduate Program, University of California - San Diego, La Jolla, California 92093-7374
| | - Ryan Golden
- Department of Medicine, University of California - San Diego, La Jolla, California 92093-7374
- Neurosciences Graduate Program, University of California - San Diego, La Jolla, California 92093-7374
| | - Maxim Bazhenov
- Department of Medicine, University of California - San Diego, La Jolla, California 92093-7374
- Neurosciences Graduate Program, University of California - San Diego, La Jolla, California 92093-7374
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Xu A, Beyeler M. Retinal ganglion cells undergo cell typeâ€"specific functional changes in a biophysically detailed model of retinal degeneration. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.13.523982. [PMID: 36711897 PMCID: PMC9882163 DOI: 10.1101/2023.01.13.523982] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Understanding the retina in health and disease is a key issue for neuroscience and neuroengineering applications such as retinal prostheses. During degeneration, the retinal network undergoes complex and multi-stage neuroanatomical alterations, which drastically impact the retinal ganglion cell (RGC) response and are of clinical importance. Here we present a biophysically detailed in silico model of retinal degeneration that simulates the network-level response to both light and electrical stimulation as a function of disease progression. The model is not only able to reproduce common findings about RGC activity in the degenerated retina, such as hyperactivity and increased electrical thresholds, but also offers testable predictions about the underlying neuroanatomical mechanisms. Overall, our findings demonstrate how biophysical changes associated with retinal degeneration affect retinal responses to both light and electrical stimulation, which may further our understanding of visual processing in the retina as well as inform the design and application of retinal prostheses.
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Madugula SS, Gogliettino AR, Zaidi M, Aggarwal G, Kling A, Shah NP, Brown JB, Vilkhu R, Hays MR, Nguyen H, Fan V, Wu EG, Hottowy P, Sher A, Litke AM, Silva RA, Chichilnisky E. Focal electrical stimulation of human retinal ganglion cells for vision restoration. J Neural Eng 2022; 19:10.1088/1741-2552/aca5b5. [PMID: 36533865 PMCID: PMC10010036 DOI: 10.1088/1741-2552/aca5b5] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 11/24/2022] [Indexed: 11/25/2022]
Abstract
Objective. Vision restoration with retinal implants is limited by indiscriminate simultaneous activation of many cells and cell types, which is incompatible with reproducing the neural code of the retina. Recent work has shown that primate retinal ganglion cells (RGCs), which transmit visual information to the brain, can be directly electrically activated with single-cell, single-spike, cell-type precision - however, this possibility has never been tested in the human retina. In this study we aim to characterize, for the first time, direct in situ extracellular electrical stimulation of individual human RGCs.Approach. Extracellular electrical stimulation of individual human RGCs was conducted in three human retinas ex vivo using a custom large-scale, multi-electrode array capable of simultaneous recording and stimulation. Measured activation properties were compared directly to extensive results from macaque.Main results. Precise activation was in many cases possible without activating overlying axon bundles, at low stimulation current levels similar to those used in macaque. The major RGC types could be identified and targeted based on their distinctive electrical signatures. The measured electrical activation properties of RGCs, combined with a dynamic stimulation algorithm, was sufficient to produce an evoked visual signal that was nearly optimal given the constraints of the interface.Significance. These results suggest the possibility of high-fidelity vision restoration in humans using bi-directional epiretinal implants.
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Affiliation(s)
- Sasidhar S. Madugula
- Neurosciences PhD Program, Stanford University, Stanford, CA, USA
- School of Medicine, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Alex R. Gogliettino
- Neurosciences PhD Program, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Moosa Zaidi
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
- School of Medicine, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Gorish Aggarwal
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Alexandra Kling
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Nishal P. Shah
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Jeff B. Brown
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
| | - Ramandeep Vilkhu
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
| | - Madeline R. Hays
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
- Department of Bioengineering, Stanford University, Stanford, CA, USA
| | - Huy Nguyen
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
| | - Victoria Fan
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
| | - Eric G. Wu
- Department of Electrical Engineering, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
| | - Pawel Hottowy
- Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow, Poland
| | - Alexander Sher
- Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA, USA
| | - Alan M. Litke
- Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA, USA
| | - Ruwan A. Silva
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
| | - E.J. Chichilnisky
- Department of Neurosurgery, Stanford University, Stanford, CA, USA
- Department of Ophthalmology, Stanford University, Stanford, CA, USA
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, USA
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8
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Ly K, Guo T, Tsai D, Muralidharan M, Shivdasani MN, Lovell NH, Dokos S. Simulating the impact of photoreceptor loss and inner retinal network changes on electrical activity of the retina. J Neural Eng 2022; 19. [PMID: 36368033 DOI: 10.1088/1741-2552/aca221] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 11/11/2022] [Indexed: 11/13/2022]
Abstract
Objective.A major reason for poor visual outcomes provided by existing retinal prostheses is the limited knowledge of the impact of photoreceptor loss on retinal remodelling and its subsequent impact on neural responses to electrical stimulation. Computational network models of the neural retina assist in the understanding of normal retinal function but can be also useful for investigating diseased retinal responses to electrical stimulation.Approach.We developed and validated a biophysically detailed discrete neuronal network model of the retina in the software package NEURON. The model includes rod and cone photoreceptors, ON and OFF bipolar cell pathways, amacrine and horizontal cells and finally, ON and OFF retinal ganglion cells with detailed network connectivity and neural intrinsic properties. By accurately controlling the network parameters, we simulated the impact of varying levels of degeneration on retinal electrical function.Main results.Our model was able to reproduce characteristic monophasic and biphasic oscillatory patterns seen in ON and OFF neurons during retinal degeneration (RD). Oscillatory activity occurred at 3 Hz with partial photoreceptor loss and at 6 Hz when all photoreceptor input to the retina was removed. Oscillations were found to gradually weaken, then disappear when synapses and gap junctions were destroyed in the inner retina. Without requiring any changes to intrinsic cellular properties of individual inner retinal neurons, our results suggest that changes in connectivity alone were sufficient to give rise to neural oscillations during photoreceptor degeneration, and significant network connectivity destruction in the inner retina terminated the oscillations.Significance.Our results provide a platform for further understanding physiological retinal changes with progressive photoreceptor and inner RD. Furthermore, our model can be used to guide future stimulation strategies for retinal prostheses to benefit patients at different stages of disease progression, particularly in the early and mid-stages of RD.
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Affiliation(s)
- Keith Ly
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW, 2052, Australia
| | - Tianruo Guo
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW, 2052, Australia
| | - David Tsai
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW, 2052, Australia.,School of Electrical Engineering & Telecommunications, UNSW, Sydney, NSW 2052, Australia
| | | | - Mohit N Shivdasani
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW, 2052, Australia
| | - Nigel H Lovell
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW, 2052, Australia.,Tyree Institute of Health Engineering (IHealthE), UNSW, Sydney, NSW 2052, Australia
| | - Socrates Dokos
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW, 2052, Australia
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Avraham D, Yitzhaky Y. Simulating the perceptual effects of electrode-retina distance in prosthetic vision. J Neural Eng 2022; 19. [PMID: 35561665 DOI: 10.1088/1741-2552/ac6f82] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Accepted: 05/13/2022] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Retinal prostheses aim to restore some vision in retinitis pigmentosa and age-related macular degeneration blind patients. Many spatial and temporal aspects have been found to affect prosthetic vision. Our objective is to study the impact of the space-variant distance between the stimulating electrodes and the surface of the retina on prosthetic vision and how to mitigate this impact. APPROACH A prosthetic vision simulation was built to demonstrate the perceptual effects of the electrode-retina distance (ERD) with different random spatial variations, such as size, brightness, shape, dropout, and spatial shifts. Three approaches for reducing the ERD effects are demonstrated: electrode grouping (quads), ERD-based input-image enhancement, and object scanning with and without phosphene persistence. A quantitative assessment for the first two approaches was done based on experiments with 20 subjects and three vision-based computational image similarity metrics. MAIN RESULTS The effects of various ERDs on phosphenes' size, brightness, and shape were simulated. Quads, chosen according to the ERDs, effectively elicit phosphenes without exceeding the safe charge density limit, whereas single electrodes with large ERD cannot do so. Input-image enhancement reduced the ERD effects effectively. These two approaches significantly improved ERD-affected prosthetic vision according to the experiment and image similarity metrics. A further reduction of the ERD effects was achieved by scanning an object while moving the head. SIGNIFICANCE ERD has multiple effects on perception with retinal prostheses. One of them is vision loss caused by the incapability of electrodes with large ERD to evoke phosphenes. The three approaches presented in this study can be used separately or together to mitigate the impact of ERD. A consideration of our approaches in reducing the perceptual effects of the ERD may help improve the perception with current prosthetic technology and influence the design of future prostheses.
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Affiliation(s)
- David Avraham
- Department of Electro-Optical Engineering, Ben-Gurion University of the Negev, 1 Ben-Gurion Blvd., Beer-Sheva, 84105, ISRAEL
| | - Yitzhak Yitzhaky
- Electro-Optical Engineering, School of Engineering, Ben-Gurion University of the Negev, 1 Ben-Gurion Blvd., Beer-Sheva, Southern, 84105, ISRAEL
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Raghuram V, Werginz P, Fried SI, Timko BP. Morphological Factors that Underlie Neural Sensitivity to Stimulation in the Retina. ADVANCED NANOBIOMED RESEARCH 2021; 1:2100069. [PMID: 35399546 PMCID: PMC8993153 DOI: 10.1002/anbr.202100069] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Retinal prostheses are a promising therapeutic intervention for patients afflicted by outer retinal degenerative diseases like retinitis pigmentosa and age-related macular degeneration. While significant advances in the development of retinal implants have been made, the quality of vision elicited by these devices remains largely sub-optimal. The variability in the responses produced by retinal devices is most likely due to the differences between the natural cell type-specific signaling that occur in the healthy retina vs. the non-specific activation of multiple cell types arising from artificial stimulation. In order to replicate these natural signaling patterns, stimulation strategies must be capable of preferentially activating specific RGC types. To design more selective stimulation strategies, a better understanding of the morphological factors that underlie the sensitivity to prosthetic stimulation must be developed. This review will focus on the role that different anatomical components play in driving the direct activation of RGCs by extracellular stimulation. Briefly, it will (1) characterize the variability in morphological properties of α-RGCs, (2) detail the influence of morphology on the direct activation of RGCs by electric stimulation, and (3) describe some of the potential biophysical mechanisms that could explain differences in activation thresholds and electrically evoked responses between RGC types.
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Affiliation(s)
- Vineeth Raghuram
- Boston VA Healthcare System, 150 S Huntington Ave, Boston, MA 02130, USA
- Dept. of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA 02155, USA
- Dept. of Neurosurgery, Massachusetts General Hospital - Harvard Medical School, 50 Blossom Street, Boston, MA, 02114
| | - Paul Werginz
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Wiedner Hauptstrasse 8-10, Vienna, Austria
- Dept. of Neurosurgery, Massachusetts General Hospital - Harvard Medical School, 50 Blossom Street, Boston, MA, 02114
| | - Shelley I. Fried
- Boston VA Healthcare System, 150 S Huntington Ave, Boston, MA 02130, USA
- Dept. of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA 02155, USA
- Dept. of Neurosurgery, Massachusetts General Hospital - Harvard Medical School, 50 Blossom Street, Boston, MA, 02114
| | - Brian P. Timko
- Dept. of Biomedical Engineering, Tufts University, 4 Colby Street, Medford, MA 02155, USA
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Yamashita K, Sundaram P, Uchida T, Matsuo T, Wong W. Modelling the visual response to an OUReP retinal prosthesis with photoelectric dye coupled to polyethylene film. J Neural Eng 2021; 18. [PMID: 33857924 DOI: 10.1088/1741-2552/abf892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 04/15/2021] [Indexed: 11/12/2022]
Abstract
Objective.Retinal prostheses have been developed to restore vision in blind patients suffering from diseases like retinitis pigmentosa.Approach.A new type of retinal prosthesis called the Okayama University-type retinal prosthesis (OUReP) was developed by chemically coupling photoelectric dyes to a polyethylene film surface. The prosthesis works by passively generating an electric potential when stimulated by light. However, the neurophysiological mechanism of how OUReP stimulates the degenerated retina is unknown.Main results.Here, we explore how the OUReP affects retinal tissues using a finite element model to solve for the potential inside the tissue and an active Hodgkin-Huxley model based on rat vision to predict the corresponding retinal bipolar response.Significance.We show that the OUReP is likely capable of eliciting responses in retinal bipolar cells necessary to generate vision under most ambient conditions.
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Affiliation(s)
- Koichiro Yamashita
- Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan
| | - Prathima Sundaram
- Department of Electrical and Computer Engineering, University of Toronto, 40 St. George Street, Toronto, ON M5S 2E4, Canada
| | - Tetsuya Uchida
- Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan
| | - Toshihiko Matsuo
- Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
| | - Willy Wong
- Department of Electrical and Computer Engineering, University of Toronto, 40 St. George Street, Toronto, ON M5S 2E4, Canada
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12
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Abbasi B, Rizzo JF. Advances in Neuroscience, Not Devices, Will Determine the Effectiveness of Visual Prostheses. Semin Ophthalmol 2021; 36:168-175. [PMID: 33734937 DOI: 10.1080/08820538.2021.1887902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Background: Innovations in engineering and neuroscience have enabled the development of sophisticated visual prosthetic devices. In clinical trials, these devices have provided visual acuities as high as 20/460, enabled coarse navigation, and even allowed for reading of short words. However, long-term commercial viability arguably rests on attaining even better vision and more definitive improvements in tasks of daily living and quality of life. Purpose: Here we review technological and biological obstacles in the implementation of visual prosthetics. Conclusions: Research in the visual prosthetic field has tackled significant technical challenges, including biocompatibility, signal spread through neural tissue, and inadvertent activation of passing axons; however, significant gaps in knowledge remain in the realm of neuroscience, including the neural code of vision and visual plasticity. We assert that further optimization of prosthetic devices alone will not provide markedly improved visual outcomes without significant advances in our understanding of neuroscience.
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Affiliation(s)
- Bardia Abbasi
- Neuro-Ophthalmology Service, Department of Ophthalmology, Massachusetts Eye and Ear and Harvard Medical School, Boston, MA, USA
| | - Joseph F Rizzo
- Neuro-Ophthalmology Service, Department of Ophthalmology, Massachusetts Eye and Ear and Harvard Medical School, Boston, MA, USA
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13
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Paknahad J, Loizos K, Humayun M, Lazzi G. Targeted Stimulation of Retinal Ganglion Cells in Epiretinal Prostheses: A Multiscale Computational Study. IEEE Trans Neural Syst Rehabil Eng 2020; 28:2548-2556. [PMID: 32991284 PMCID: PMC7737501 DOI: 10.1109/tnsre.2020.3027560] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Retinal prostheses aim at restoring partial sight to patients that are blind due to retinal degenerative diseases by electrically stimulating the surviving healthy retinal neurons. Ideally, the electrical stimulation of the retina is intended to induce localized, focused, percepts only; however, some epiretinal implant subjects have reported seeing elongated phosphenes in a single electrode stimulation due to the axonal activation of retinal ganglion cells (RGCs). This issue can be addressed by properly devising stimulation waveforms so that the possibility of inducing axonal activation of RGCs is minimized. While strategies to devise electrical stimulation waveforms to achieve a focal RGCs response have been reported in literature, the underlying mechanisms are not well understood. This article intends to address this gap; we developed morphologically and biophysically realistic computational models of two classified RGCs: D1-bistratified and A2-monostratified. Computational results suggest that the sodium channel band (SOCB) is less sensitive to modulations in stimulation parameters than the distal axon (DA), and DA stimulus threshold is less sensitive to physiological differences among RGCs. Therefore, over a range of RGCs distal axon diameters, short-pulse symmetric biphasic waveforms can enhance the stimulation threshold difference between the SOCB and the DA. Appropriately designed waveforms can avoid axonal activation of RGCs, implying a consequential reduction of undesired strikes in the visual field.
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Haji Ghaffari D, Finn KE, Jeganathan VSE, Patel U, Wuyyuru V, Roy A, Weiland JD. The effect of waveform asymmetry on perception with epiretinal prostheses. J Neural Eng 2020; 17:045009. [PMID: 32590371 DOI: 10.1088/1741-2552/aba07e] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Objective Retinal prosthetic implants have helped improve vision in patients blinded by photoreceptor degeneration. Retinal implant users report improvements in light perception and performing visual tasks, but their ability to perceive shapes and letters is limited due to the low precision of retinal activation, which is exacerbated by axonal stimulation and high perceptual thresholds. A previous in vitro study in our lab used calcium imaging to measure the spatial activity of mouse retinal ganglion cells (RGCs) in response to electrical stimulation. Based on this study, symmetric anodic-first (SA) stimulation effectively avoided axonal activation and asymmetric anodic-first stimulation (AA) with duration ratios (ratio of the anodic to cathodic phase) greater than 10 reduced RGC activation thresholds significantly. Applying these novel stimulation strategies in clinic may increase perception precision and improve the overall patient outcomes. Approach We combined human subject testing and computational modeling to further examine the effect of SA and AA stimuli on perception shapes and thresholds for epiretinal stimulation of RGCs. Main results Threshold measurement in three Argus II participants indicated that AA stimulation could increase perception probabilities compared to a standard symmetric cathodic-first (SC) pulse, and this effect can be intensified by addition of an interphae gap (IPG). Our in silico RGC model predicts lower thresholds with AA and asymmetric cathodic-first (AC) stimuli compared to a SC pulse. This effect was more pronounced at shorter pulse widths. The most effective pulse for threshold reduction with short pulse durations (≤0.12 ms) was AA stimulation with small duration ratios (≤5) and long IPGs (≥2 ms). For the 0.5 ms pulse duration, SC stimulation with IPGs longer than 0.5 ms, or asymmetric stimuli with large duration ratios (≥20) were most effective in threshold reduction. Phosphene shape analysis did not reveal a significant change in percept elongation with SA stimulation. However, there was a significant increase in percept size (P < 0.01) with AA stimulation compared to the standard pulse in one participant. Significane Including asymmetric waveform capability will provide more flexible options for optimization and personalized fitting of retinal implants.
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Affiliation(s)
- Dorsa Haji Ghaffari
- Department of Biomedical Engineering, Michigan Engineering, University of Michigan, Ann Arbor, MI 48109, United States of America. Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109, United States of America
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15
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Werginz P, Wang BY, Chen ZC, Palanker D. On optimal coupling of the 'electronic photoreceptors' into the degenerate retina. J Neural Eng 2020; 17:045008. [PMID: 32613948 PMCID: PMC10948023 DOI: 10.1088/1741-2552/aba0d2] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Objective To restore sight in atrophic age-related macular degeneration, the lost photoreceptors can be replaced with electronic implants, which replicate their two major functions: (1) converting light into an electric signal, and (2) transferring visual information to the secondary neurons in the retinal neural network—the bipolar cells (BC). We study the selectivity of BC activation by subretinal implants and dynamics of their response to pulsatile waveforms in order to optimize the electrical stimulation scheme such that retinal signal processing with 'electronic photoreceptors' remains as close to natural as possible. Approach A multicompartmental model of a BC was implemented to simulate responses of the voltage-gated calcium channels and subsequent synaptic vesicle release under continuous and pulsatile stimuli. We compared the predicted response under various frequencies, pulse durations, and alternating gratings to the corresponding experimental measurements. In addition, electric field was computed for various electrode configurations in a 3-d finite element model to assess the stimulation selectivity via spatial confinement of the field. Main results The modeled BC-mediated retinal responses were, in general, in good agreement with previously published experimental results. Kinetics of the calcium pumps and of the neurotransmitter release in ribbon synapses, which underpin the BC's temporal filtering and rectifying functions, allow mimicking the natural BC response with high frequency pulsatile stimulation, thereby preserving features of the retinal signal processing, such as flicker fusion, adaptation to static stimuli and non-linear summation of subunits in receptive field. Selectivity of the BC stimulation while avoiding direct activation of the downstream neurons (amacrine and ganglion cells—RGCs) is improved with local return electrodes. Significance If the retinal neural network is preserved to a large extent in age-related macular degeneration, selective stimulation of BCs with proper spatial and temporal modulation of the extracellular electric field may retain many features of the natural retinal signal processing and hence allow highly functional restoration of sight.
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Affiliation(s)
- Paul Werginz
- Institute for Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria. Author to whom any correspondence should be adressed
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16
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Stieger KC, Eles JR, Ludwig KA, Kozai TDY. In vivo microstimulation with cathodic and anodic asymmetric waveforms modulates spatiotemporal calcium dynamics in cortical neuropil and pyramidal neurons of male mice. J Neurosci Res 2020; 98:2072-2095. [PMID: 32592267 DOI: 10.1002/jnr.24676] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 05/26/2020] [Accepted: 05/27/2020] [Indexed: 12/12/2022]
Abstract
Electrical stimulation has been critical in the development of an understanding of brain function and disease. Despite its widespread use and obvious clinical potential, the mechanisms governing stimulation in the cortex remain largely unexplored in the context of pulse parameters. Modeling studies have suggested that modulation of stimulation pulse waveform may be able to control the probability of neuronal activation to selectively stimulate either cell bodies or passing fibers depending on the leading polarity. Thus, asymmetric waveforms with equal charge per phase (i.e., increasing the leading phase duration and proportionately decreasing the amplitude) may be able to activate a more spatially localized or distributed population of neurons if the leading phase is cathodic or anodic, respectively. Here, we use two-photon and mesoscale calcium imaging of GCaMP6s expressed in excitatory pyramidal neurons of male mice to investigate the role of pulse polarity and waveform asymmetry on the spatiotemporal properties of direct neuronal activation with 10-Hz electrical stimulation. We demonstrate that increasing cathodic asymmetry effectively reduces neuronal activation and results in a more spatially localized subpopulation of activated neurons without sacrificing the density of activated neurons around the electrode. Conversely, increasing anodic asymmetry increases the spatial spread of activation and highly resembles spatiotemporal calcium activity induced by conventional symmetric cathodic stimulation. These results suggest that stimulation polarity and asymmetry can be used to modulate the spatiotemporal dynamics of neuronal activity thus increasing the effective parameter space of electrical stimulation to restore sensation and study circuit dynamics.
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Affiliation(s)
- Kevin C Stieger
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.,Center for the Neural Basis of Cognition, University of Pittsburgh, Carnegie Mellon University, Pittsburgh, PA, USA
| | - James R Eles
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Kip A Ludwig
- Department of Biomedical Engineering, University of Wisconsin Madison, Madison, WI, USA.,Department of Neurological Surgery, University of Wisconsin Madison, Madison, WI, USA.,Wisconsin Institute for Translational Neuroengineering (WITNe), Madison, WI, USA
| | - Takashi D Y Kozai
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.,Center for the Neural Basis of Cognition, University of Pittsburgh, Carnegie Mellon University, Pittsburgh, PA, USA.,Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, USA.,NeuroTech Center, University of Pittsburgh Brain Institute, Pittsburgh, PA, USA
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Lyu Q, Lu Z, Li H, Qiu S, Guo J, Sui X, Sun P, Li L, Chai X, Lovell NH. A Three-Dimensional Microelectrode Array to Generate Virtual Electrodes for Epiretinal Prosthesis Based on a Modeling Study. Int J Neural Syst 2020; 30:2050006. [DOI: 10.1142/s0129065720500069] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Despite many advances in the development of retinal prostheses, clinical reports show that current retinal prosthesis subjects can only perceive prosthetic vision with poor visual acuity. A possible approach for improving visual acuity is to produce virtual electrodes (VEs) through electric field modulation. Generating controllable and localized VEs is a crucial factor in effectively improving the perceptive resolution of the retinal prostheses. In this paper, we aimed to design a microelectrode array (MEA) that can produce converged and controllable VEs by current steering stimulation strategies. Through computational modeling, we designed a three-dimensional concentric ring–disc MEA and evaluated its performance with different stimulation strategies. Our simulation results showed that electrode–retina distance (ERD) and inter-electrode distance (IED) can dramatically affect the distribution of electric field. Also the converged VEs could be produced when the parameters of the three-dimensional MEA were appropriately set. VE sites can be controlled by manipulating the proportion of current on each adjacent electrode in a current steering group (CSG). In addition, spatial localization of electrical stimulation can be greatly improved under quasi-monopolar (QMP) stimulation. This study may provide support for future application of VEs in epiretinal prosthesis for potentially increasing the visual acuity of prosthetic vision.
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Affiliation(s)
- Qing Lyu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Zhuofan Lu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Heng Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Shirong Qiu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Jiahui Guo
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Xiaohong Sui
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Pengcheng Sun
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Liming Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Xinyu Chai
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Nigel H. Lovell
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW 2052, Australia
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Chenais NAL, Leccardi MJIA, Ghezzi D. Capacitive-like photovoltaic epiretinal stimulation enhances and narrows the network-mediated activity of retinal ganglion cells by recruiting the lateral inhibitory network. J Neural Eng 2019; 16:066009. [DOI: 10.1088/1741-2552/ab3913] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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19
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Wang B, Aberra AS, Grill WM, Peterchev AV. Modified cable equation incorporating transverse polarization of neuronal membranes for accurate coupling of electric fields. J Neural Eng 2019; 15:026003. [PMID: 29363622 DOI: 10.1088/1741-2552/aa8b7c] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE We present a theory and computational methods to incorporate transverse polarization of neuronal membranes into the cable equation to account for the secondary electric field generated by the membrane in response to transverse electric fields. The effect of transverse polarization on nonlinear neuronal activation thresholds is quantified and discussed in the context of previous studies using linear membrane models. APPROACH The response of neuronal membranes to applied electric fields is derived under two time scales and a unified solution of transverse polarization is given for spherical and cylindrical cell geometries. The solution is incorporated into the cable equation re-derived using an asymptotic model that separates the longitudinal and transverse dimensions. Two numerical methods are proposed to implement the modified cable equation. Several common neural stimulation scenarios are tested using two nonlinear membrane models to compare thresholds of the conventional and modified cable equations. MAIN RESULTS The implementations of the modified cable equation incorporating transverse polarization are validated against previous results in the literature. The test cases show that transverse polarization has limited effect on activation thresholds. The transverse field only affects thresholds of unmyelinated axons for short pulses and in low-gradient field distributions, whereas myelinated axons are mostly unaffected. SIGNIFICANCE The modified cable equation captures the membrane's behavior on different time scales and models more accurately the coupling between electric fields and neurons. It addresses the limitations of the conventional cable equation and allows sound theoretical interpretations. The implementation provides simple methods that are compatible with current simulation approaches to study the effect of transverse polarization on nonlinear membranes. The minimal influence by transverse polarization on axonal activation thresholds for the nonlinear membrane models indicates that predictions of stronger effects in linear membrane models with a fixed activation threshold are inaccurate. Thus, the conventional cable equation works well for most neuroengineering applications, and the presented modeling approach is well suited to address the exceptions.
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Affiliation(s)
- Boshuo Wang
- Department of Psychiatry and Behavioral Sciences, School of Medicine, Duke University, Durham, NC 27710, United States of America
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20
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Chang YC, Haji Ghaffari D, Chow RH, Weiland JD. Stimulation strategies for selective activation of retinal ganglion cell soma and threshold reduction. J Neural Eng 2019; 16:026017. [PMID: 30560810 PMCID: PMC6648650 DOI: 10.1088/1741-2552/aaf92b] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
OBJECTIVE Retinal prosthetic implants restore partial vision to patients blinded due to outer retinal degeneration, using a camera-guided multielectrode array (MEA) that electrically stimulates surviving retinal neurons. Commercial epi-retinal prostheses use millisecond-scale charge-balanced, symmetric, cathodic-first biphasic pulses to depolarize retinal ganglion cells (RGCs) and bipolar cells (BCs), frequently creating oblong perceptions of light related to axonal activation of RGCs. Stimulation strategies that avoid axonal stimulation and decrease the threshold of targeted neurons may significantly improve prosthetic vision in terms of spatial resolution and power efficiency. APPROACH We developed a virus-transduced genetically encoded calcium indicator (GECI) GCaMP6f and microscopy platform for calcium imaging to record the neural activity from RGCs at single-cell resolution in wholemount retinas. Multiple stimulation paradigms were applied through a microelectrode array (MEA) with transparent indium tin oxide electrodes. The evoked neuronal activities were converted to corresponding 2D calcium imaging transient pattern and spatial threshold map to identify the ideal focal response which corresponds to optimal percept in patient. MAIN RESULTS The proposed optical system with GCaMP6f is capable of recording from population of mouse RGCs in real time during electrical stimulation with precise location information relative to the stimulation sites. Optimal duration and phase order of pulse were identified to avoid axonal stimulation and selectively activate targeted RGC somas, without requiring a significant increase in stimulation charge. Additionally, we show that reduced stimulus threshold can be achieved with the special design of asymmetric anodic-first pulse. SIGNIFICANCE Our findings support the possibility of manipulating the responses of RGCs through varying the stimulation waveform. Focal response can be achieved with relative short duration (⩽120 μs) pulses, and can be improved by reversing the standard phase order. The RGCs threshold can be significantly reduced by 33.3%-50% in terms of charge through applying hyperpolarizing pre-pulses with a 20:1 ratio (pre-pulse:stimulus pulse). The results support the future retinal prosthesis design that potentially forms more ideal shape perception with higher spatial resolution and power efficiency.
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Affiliation(s)
- Yao-Chuan Chang
- Center for Bioelectronic Medicine & Biomedical Science, Feinstein Institute for Medical Research, Manhasset, NY 11030, United States of America
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21
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Shalbaf F, Lovell NH, Dokos S, Trew M, Vaghefi E. Foveal eccentricity can influence activation threshold in subretinal electrical stimulation. Biomed Phys Eng Express 2019. [DOI: 10.1088/2057-1976/ab0b85] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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22
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Rathbun DL, Ghorbani N, Shabani H, Zrenner E, Hosseinzadeh Z. Spike-triggered average electrical stimuli as input filters for bionic vision—a perspective. J Neural Eng 2018; 15:063002. [DOI: 10.1088/1741-2552/aae493] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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23
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Esler TB, Maturana MI, Kerr RR, Grayden DB, Burkitt AN, Meffin H. Biophysical basis of the linear electrical receptive fields of retinal ganglion cells. J Neural Eng 2018; 15:055001. [PMID: 29889051 DOI: 10.1088/1741-2552/aacbaa] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Responses of retinal ganglion cells to direct electrical stimulation have been shown experimentally to be well described by linear-nonlinear models. These models rely on the simplifying assumption that retinal ganglion cell responses to stimulation with an array of electrodes are driven by a simple linear weighted sum of stimulus current amplitudes from each electrode, known as the 'electrical receptive field'. OBJECTIVE This paper aims to demonstrate the biophysical basis of the linear-nonlinear model and the electrical receptive field to facilitate the development of improved stimulation strategies for retinal implants. APPROACH We compare the linear-nonlinear model of subretinal electrical stimulation with a multi-layered, biophysical, volume conductor model of retinal stimulation. MAIN RESULTS Our results show that the linear electrical receptive field of the linear-nonlinear model matches the transmembrane currents induced by electrodes (the activating function) at the site of the high-density sodium channel band with only minor discrepancies. The discrepancies are mostly eliminated by including axial current flow originating from adjacent cell compartments. Furthermore, for cells where a single linear electrical receptive field is insufficient, we show that cell responses are likely driven by multiple sites of action potential initiation with multiple distinct receptive fields, each of which can be accurately described by the activating function. SIGNIFICANCE This result establishes that the biophysical basis of the electrical receptive field of the linear-nonlinear model is the superposition of transmembrane currents induced by different electrodes at and near the site of action potential initiation. Together with existing experimental support for linear-nonlinear models of electrical stimulation, this provides a firm basis for using this much simplified model to generate more optimal stimulation patterns for retinal implants.
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Affiliation(s)
- Timothy B Esler
- NeuroEngineering Laboratory, Department of Biomedical Engineering, The University of Melbourne, Australia
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24
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Walston ST, Chow RH, Weiland JD. Direct measurement of bipolar cell responses to electrical stimulation in wholemount mouse retina. J Neural Eng 2018. [PMID: 29513646 DOI: 10.1088/1741-2552/aab4ed] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
OBJECTIVE This in vitro investigation examines the response of retinal bipolar cells to extracellular electrical stimulation. APPROACH In vitro investigations characterizing the response of retinal neurons to electrical stimulation have primarily focused on retinal ganglion cells because they are the output neurons of the retina and their superficial position in the retina makes them readily accessible to in vitro recording techniques. Thus, the majority of information regarding the response of inner retinal neurons has been inferred from ganglion cell activity. Here we use patch clamp electrophysiology to directly record electrically-evoked activity in bipolar cells within the inner retina of normal Tg(Gng13-EGFP)GI206Gsat and degenerate rd10 Tg(Gng13-EGFP)GI206Gsat mice using a wholemount preparation. MAIN RESULTS Bipolar cells respond to electrical stimulation with time-locked depolarizing voltage transients. The latency of the response declines with increases in stimulation amplitude. A desensitizing response is observed during repeated stimulation with 25 ms biphasic current pulses delivered at pulse rates greater than 6 pps. A burst of long-latency (200-1000 ms) inhibitory postsynaptic potentials are evoked by the stimulus and the burst exhibits evidence of a lower and upper stimulation threshold. SIGNIFICANCE These results provide insights into the various types of bipolar cell activity elicited by electrical stimulation and may be useful for future retinal prosthesis stimulation protocols. This investigation uses patch clamp electrophysiology to provide direct analysis of ON-type bipolar cell responses to electrical stimulation in a wholemount retina preparation. It explores the effects of variable stimulus amplitudes, pulse widths, and frequencies in both normal and degenerate retina. The analysis adds to a body of work largely based upon indirect measurements of bipolar cell activity, and the methodology demonstrates an alternative retina preparation technique in which to acquire single-cell activity.
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Affiliation(s)
- Steven T Walston
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90007, United States of America
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Esler TB, Kerr RR, Tahayori B, Grayden DB, Meffin H, Burkitt AN. Minimizing activation of overlying axons with epiretinal stimulation: The role of fiber orientation and electrode configuration. PLoS One 2018; 13:e0193598. [PMID: 29494655 PMCID: PMC5833203 DOI: 10.1371/journal.pone.0193598] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2017] [Accepted: 02/14/2018] [Indexed: 12/19/2022] Open
Abstract
Currently, a challenge in electrical stimulation of the retina with a visual prosthesis (bionic eye) is to excite only the cells lying directly under the electrode in the ganglion cell layer, while avoiding excitation of axon bundles that pass over the surface of the retina in the nerve fiber layer. Stimulation of overlying axons results in irregular visual percepts, limiting perceptual efficacy. This research explores how differences in fiber orientation between the nerve fiber layer and ganglion cell layer leads to differences in the electrical activation of the axon initial segment and axons of passage. Approach. Axons of passage of retinal ganglion cells in the nerve fiber layer are characterized by a narrow distribution of fiber orientations, causing highly anisotropic spread of applied current. In contrast, proximal axons in the ganglion cell layer have a wider distribution of orientations. A four-layer computational model of epiretinal extracellular stimulation that captures the effect of neurite orientation in anisotropic tissue has been developed using a volume conductor model known as the cellular composite model. Simulations are conducted to investigate the interaction of neural tissue orientation, stimulating electrode configuration, and stimulation pulse duration and amplitude. Main results. Our model shows that simultaneous stimulation with multiple electrodes aligned with the nerve fiber layer can be used to achieve selective activation of axon initial segments rather than passing fibers. This result can be achieved while reducing required stimulus charge density and with only modest increases in the spread of activation in the ganglion cell layer, and is shown to extend to the general case of arbitrary electrode array positioning and arbitrary target volume. Significance. These results elucidate a strategy for more targeted stimulation of retinal ganglion cells with experimentally-relevant multi-electrode geometries and achievable stimulation requirements.
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Affiliation(s)
- Timothy B. Esler
- Department of Biomedical Engineering, The University of Melbourne, Parkville, Victoria, Australia
- * E-mail:
| | - Robert R. Kerr
- Department of Biomedical Engineering, The University of Melbourne, Parkville, Victoria, Australia
- Seer Medical, Melbourne, Victoria, Australia
| | - Bahman Tahayori
- Monash Institute of Medical Engineering, Monash University, Clayton, Victoria, Australia
| | - David B. Grayden
- Department of Biomedical Engineering, The University of Melbourne, Parkville, Victoria, Australia
- Centre for Neural Engineering, The University of Melbourne, Parkville, Victoria, Australia
| | - Hamish Meffin
- National Vision Research Institute, Australian College of Optometry, Carlton, Victoria, Australia
- ARC Centre of Excellence for Integrative Brain Function, Optometry & Vision Science, The University of Melbourne, Parkville, Victoria, Australia
| | - Anthony N. Burkitt
- Department of Biomedical Engineering, The University of Melbourne, Parkville, Victoria, Australia
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Weiland JD, Walston ST, Humayun MS. Electrical Stimulation of the Retina to Produce Artificial Vision. Annu Rev Vis Sci 2018; 2:273-294. [PMID: 28532361 DOI: 10.1146/annurev-vision-111815-114425] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Retinal prostheses aim to restore vision to blind individuals suffering from retinal diseases such as retinitis pigmentosa and age-related macular degeneration. These devices function by electrically stimulating surviving retinal neurons, whose activation is interpreted by the brain as a visual percept. Many prostheses are currently under development. They are categorized as epiretinal, subretinal, and suprachoroidal prostheses on the basis of the placement of the stimulating microelectrode array. Each can activate ganglion cells through direct or indirect stimulation. The response of retinal neurons to these modes of stimulation are discussed in detail and are placed in context of the visual percept they are likely to evoke. This article further reviews challenges faced by retinal prosthesis and discusses potential solutions to address them.
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Affiliation(s)
- James D Weiland
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California 90007; .,USC Roski Eye Institute, University of Southern California, Los Angeles, California 90033.,Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, California 90033
| | - Steven T Walston
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California 90007;
| | - Mark S Humayun
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California 90007; .,USC Roski Eye Institute, University of Southern California, Los Angeles, California 90033.,Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, California 90033
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Rattay F, Bassereh H, Fellner A. Impact of Electrode Position on the Elicitation of Sodium Spikes in Retinal Bipolar Cells. Sci Rep 2017; 7:17590. [PMID: 29242502 PMCID: PMC5730545 DOI: 10.1038/s41598-017-17603-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 11/29/2017] [Indexed: 01/29/2023] Open
Abstract
Bipolar cells of the magnocellular pathway in the primate retina can generate action potentials because they have an axonal segment with high sodium channel density, comparable to the sodium channel band in retinal ganglion cells or pyramidal cells. The similarity between the non-human primate and the human retina is of interest for the research on retinal implants for the blind, and especially, the conditions to elicit sodium spikes in bipolar cells using extracellular stimulation. A comparison of excitation characteristics of three model neurons, a bipolar cell, a retinal ganglion cell, and a cortical pyramidal cell, demonstrates the similarities and differences regarding stimulation with microelectrodes. Moving a microelectrode parallel to the axon of a neuron commonly allows to generate spikes for every position - and this rule holds both for cathodic and anodic pulses. However, for the simulated bipolar cell anodic pulses cannot generate sodium spikes directly. Further, there is only a small region for electrode placing where extracellular cathodic stimulation causes direct spike initiation in the sodium channel band. For all other positions, a sodium spike can only be generated by antidromic current flow originating from strongly depolarized terminals.
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Affiliation(s)
- Frank Rattay
- Institute of Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria.
| | - Hassan Bassereh
- Institute of Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria
| | - Andreas Fellner
- Institute of Analysis and Scientific Computing, Vienna University of Technology, Vienna, Austria
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28
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Chang YC, Weiland JD. Stimulation Strategies for Selective Activation of Retinal Ganglion Cells. INTERNATIONAL IEEE/EMBS CONFERENCE ON NEURAL ENGINEERING : [PROCEEDINGS]. INTERNATIONAL IEEE EMBS CONFERENCE ON NEURAL ENGINEERING 2017; 2017:345-348. [PMID: 31391873 DOI: 10.1109/ner.2017.8008361] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Retinal prosthetic implants have shown potential to restore partial vision to patients blinded by retinitis pigmentosa or dry age-related macular degeneration, via a camera-driven multielectrode array that electrically stimulates surviving retinal neurons. Commercial epi-retinal prostheses mostly use charge-balanced symmetric cathodic-first biphasic pulses to depolarize retinal ganglion cells (RGCs) and bipolar cells (BCs), resulting in the perception of light in blind patients. However, previous clinical study for patients with Argus II epiretinal implants reported most percepts evoked by single electrode stimulation were elongated and aligned with estimated axon path of retinal ganglion cells, suggesting the activation of axon bundles. In this project, using an established genetically encoded calcium indicator (GECI), we performed in vitro calcium imaging for different stimulation paradigms, focusing primarily on short duration pulse that can avoid axonal stimulation and selective activate targeted RGC soma. The findings support the possibility to manipulate the responses of RGCs through varying the stimulation waveform, thus potentially forming more ideal shape perception with higher spatial resolution in future retinal prosthesis design.
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Affiliation(s)
- Yao-Chuan Chang
- University of Southern California, Los Angeles, CA 90033, USA
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29
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Esler T, Burkitt AN, Grayden DB, Kerr RR, Tahayori B, Meffin H. A computational model of orientation-dependent activation of retinal ganglion cells. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2017; 2016:5447-5450. [PMID: 28269490 DOI: 10.1109/embc.2016.7591959] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Currently, a challenge in electrical stimulation for epiretinal prostheses is the avoidance of stimulation of axons of passage in the nerve fiber layer that originate from distant regions of the ganglion cell layer. A computational model of extracellular stimulation that captures the effect of neurite orientation in anisotropic tissue is developed using a modified version of the standard volume conductor model, known as the cellular composite model, embedded in a four layer model of the retina. Simulations are conducted to investigate the interaction of neural tissue orientation, electrode placement, and stimulation pulse duration and amplitude. Using appropriate multiple electrode configurations and higher frequency stimulation, preferential activation of the axon initial segment is shown to be possible for a range of realistic electrode-retina separation distances. These results establish a quantitative relationship between the time-course of stimulation and physical properties of the tissue, such as fiber orientation.
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Eleftheriou CG, Zimmermann JB, Kjeldsen HD, David-Pur M, Hanein Y, Sernagor E. Carbon nanotube electrodes for retinal implants: A study of structural and functional integration over time. Biomaterials 2016; 112:108-121. [PMID: 27760395 PMCID: PMC5123641 DOI: 10.1016/j.biomaterials.2016.10.018] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2016] [Revised: 10/08/2016] [Accepted: 10/11/2016] [Indexed: 12/15/2022]
Abstract
The choice of electrode material is of paramount importance in neural prosthetic devices. Electrodes must be biocompatible yet able to sustain repetitive current injections in a highly corrosive environment. We explored the suitability of carbon nanotube (CNT) electrodes to stimulate retinal ganglion cells (RGCs) in a mouse model of outer retinal degeneration. We investigated morphological changes at the bio-hybrid interface and changes in RGC responses to electrical stimulation following prolonged in vitro coupling to CNT electrodes. We observed gradual remodelling of the inner retina to incorporate CNT assemblies. Electrophysiological recordings demonstrate a progressive increase in coupling between RGCs and the CNT electrodes over three days, characterized by a gradual decrease in stimulation thresholds and increase in cellular recruitment. These results provide novel evidence for time-dependent formation of viable bio-hybrids between CNTs and the retina, demonstrating that CNTs are a promising material for inclusion in retinal prosthetic devices.
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Affiliation(s)
- Cyril G Eleftheriou
- Institute of Neuroscience, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, United Kingdom
| | - Jonas B Zimmermann
- Institute of Neuroscience, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, United Kingdom
| | - Henrik D Kjeldsen
- Institute of Neuroscience, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, United Kingdom
| | - Moshe David-Pur
- School of Electrical Engineering, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel
| | - Yael Hanein
- School of Electrical Engineering, Tel-Aviv University, Ramat-Aviv, Tel-Aviv, 69978, Israel
| | - Evelyne Sernagor
- Institute of Neuroscience, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, United Kingdom.
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31
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Goetz GA, Palanker DV. Electronic approaches to restoration of sight. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2016; 79:096701. [PMID: 27502748 PMCID: PMC5031080 DOI: 10.1088/0034-4885/79/9/096701] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Retinal prostheses are a promising means for restoring sight to patients blinded by the gradual atrophy of photoreceptors due to retinal degeneration. They are designed to reintroduce information into the visual system by electrically stimulating surviving neurons in the retina. This review outlines the concepts and technologies behind two major approaches to retinal prosthetics: epiretinal and subretinal. We describe how the visual system responds to electrical stimulation. We highlight major differences between direct encoding of the retinal output with epiretinal stimulation, and network-mediated response with subretinal stimulation. We summarize results of pre-clinical evaluation of prosthetic visual functions in- and ex vivo, as well as the outcomes of current clinical trials of various retinal implants. We also briefly review alternative, non-electronic, approaches to restoration of sight to the blind, and conclude by suggesting some perspectives for future advancement in the field.
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Affiliation(s)
- G A Goetz
- Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA. Neurosurgery, Stanford University, Stanford, CA 94305, USA
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32
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Werginz P, Rattay F. The impact of calcium current reversal on neurotransmitter release in the electrically stimulated retina. J Neural Eng 2016; 13:046013. [DOI: 10.1088/1741-2560/13/4/046013] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Loizos K, RamRakhyani AK, Anderson J, Marc R, Lazzi G. On the computation of a retina resistivity profile for applications in multi-scale modeling of electrical stimulation and absorption. Phys Med Biol 2016; 61:4491-505. [PMID: 27223656 DOI: 10.1088/0031-9155/61/12/4491] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This study proposes a methodology for computationally estimating resistive properties of tissue in multi-scale computational models, used for studying the interaction of electromagnetic fields with neural tissue, with applications to both dosimetry and neuroprosthetics. Traditionally, models at bulk tissue- and cellular-level scales are solved independently, linking resulting voltage from existing resistive tissue-scale models as extracellular sources to cellular models. This allows for solving the effects that external electric fields have on cellular activity. There are two major limitations to this approach: first, the resistive properties of the tissue need to be chosen, of which there are contradicting measurements in literature; second, the measurements of resistivity themselves may be inaccurate, leading to the mentioned contradicting results found across different studies. Our proposed methodology allows for constructing computed resistivity profiles using knowledge of only the neural morphology within the multi-scale model, resulting in a practical implementation of the effective medium theory; this bypasses concerns regarding the choice of resistive properties and accuracy of measurement setups. A multi-scale model of retina is constructed with an external electrode to serve as a test bench for analyzing existing and resulting resistivity profiles, and validation is presented through the reconstruction of a published resistivity profile of retina tissue. Results include a computed resistivity profile of retina tissue for use with a retina multi-scale model used to analyze effects of external electric fields on neural activity.
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Affiliation(s)
- Kyle Loizos
- Department of Electrical and Computer Engineering, University of Utah, UT 84112, USA
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34
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Analytical solution for time-dependent potentials in a fiber stimulated by an external electrode. Med Biol Eng Comput 2016; 54:1719-1725. [DOI: 10.1007/s11517-016-1459-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 01/29/2016] [Indexed: 10/22/2022]
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Guo T, Tsai D, Morley JW, Suaning GJ, Kameneva T, Lovell NH, Dokos S. Electrical activity of ON and OFF retinal ganglion cells: a modelling study. J Neural Eng 2016; 13:025005. [PMID: 26905646 DOI: 10.1088/1741-2560/13/2/025005] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Retinal ganglion cells (RGCs) demonstrate a large range of variation in their ionic channel properties and morphologies. Cell-specific properties are responsible for the unique way RGCs process synaptic inputs, as well as artificial electrical signals such as that from a visual prosthesis. A cell-specific computational modelling approach allows us to examine the functional significance of regional membrane channel expression and cell morphology. APPROACH In this study, an existing RGC ionic model was extended by including a hyperpolarization activated non-selective cationic current as well as a T-type calcium current identified in recent experimental findings. Biophysically-defined model parameters were simultaneously optimized against multiple experimental recordings from ON and OFF RGCs. MAIN RESULTS With well-defined cell-specific model parameters and the incorporation of detailed cell morphologies, these models were able to closely reconstruct and predict ON and OFF RGC response properties recorded experimentally. SIGNIFICANCE The resulting models were used to study the contribution of different ion channel properties and spatial structure of neurons to RGC activation. The techniques of this study are generally applicable to other excitable cell models, increasing the utility of theoretical models in accurately predicting the response of real biological neurons.
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Affiliation(s)
- Tianruo Guo
- Graduate School of Biomedical Engineering, UNSW Australia, Sydney, NSW 2052, Australia
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Al Abed A, Lovell NH, Suaning G, Dokos S. A model of electrical stimulation of a retinal cell population using a multi-electrode array. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:2287-90. [PMID: 26736749 DOI: 10.1109/embc.2015.7318849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A novel computational modelling approach is employed to investigate the response of a population of retinal ganglion cells (RGCs) to external electrical stimulation. Current is delivered via a multi-electrode array design that would be employed in a future retinal prosthesis device being developed by our group. The RGCs are morphologically realistic and allow examination of the biophysical responses of intracellular compartments to externally applied currents. A number of stimulation paradigms are simulated including the use of monopolar, hexapolar and quasi-monopolar return paths. The model provides a powerful simulation tool to test and optimize electrical stimulation strategies for future retinal prosthesis devices.
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Shalbaf F, Du P, Lovell NH, Dokos S, Vaghefi E. A 3D-continuum bidomain model of retinal electrical stimulation using an anatomically detailed mesh. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:2291-4. [PMID: 26736750 DOI: 10.1109/embc.2015.7318850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A continuum bidomain model of sub-retinal electrical stimulation on an anatomically detailed mesh of retina is presented. The underlying geometry is made up of 256 B-scans of optical coherence tomography (OCT) images of a healthy human retina, covering approximately 6×2 mm(2) centered on the macula. The OCT images are initially segmented and digitized into five major retinal layers comprising passive and active retinal cell types. This computational mesh is then used to model a subretinal hexapolar biphasic electrical stimulation. Our results indicate that the ultra-structure of the retina results in an asymmetric spatial extracellular potential distribution, leading to an irregular pattern of retinal ganglion cell activation. This finding is in contrast to focal circular activation previously reported in retinal electrical stimulation modeling with a uniform mesh.
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Luo YHL, da Cruz L. The Argus® II Retinal Prosthesis System. Prog Retin Eye Res 2016; 50:89-107. [PMID: 26404104 DOI: 10.1016/j.preteyeres.2015.09.003] [Citation(s) in RCA: 188] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Revised: 08/25/2015] [Accepted: 09/17/2015] [Indexed: 11/25/2022]
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Cao X, Sui X, Lyu Q, Li L, Chai X. Effects of different three-dimensional electrodes on epiretinal electrical stimulation by modeling analysis. J Neuroeng Rehabil 2015; 12:73. [PMID: 26311232 PMCID: PMC4551567 DOI: 10.1186/s12984-015-0065-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 08/19/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. The design of stimulating electrodes plays a crucial role in the performance of epiretinal prostheses. The objective of this study was to investigate, through computational modeling analysis, the effects on the excitation of retinal ganglion cells (RGCs) when different three-dimensional (3-D) electrodes were placed in the epiretinal space. METHODS 3-D finite element models of retinal electrical stimulation were created in COMSOL using a platinum microelectrode, a vitreous body, multi-layered retinal tissue, and retinal pigment epithelium (RPE). Disk and non-planar electrodes with different 3-D structures were used in the epiretinal electrical stimulation. In addition, a multi-RGC model including ionic mechanisms was constructed in NEURON to study the excitability of RGCs in response to epiretinal electrical stimulation by different types of electrodes. Threshold current, threshold charge density, and the activated RGC area were the three key factors used to evaluate the stimulating electrode's performance. RESULTS As the electrode-retina distance increased, both threshold current and threshold charge density showed an approximately linear relationship. Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density. Non-planar electrodes evoked different activation responses in RGCs than the disk electrode. Concave electrodes produced superior stimulation localization and electrode safety while convex electrodes performed relatively poorly. CONCLUSIONS Investigation of epiretinal electrical stimulation using different 3-D electrodes would further the optimization of electrode design and help improve the performance of epiretinal prostheses. The combination of finite element analysis in COMSOL and NEURON software provides an efficient way to evaluate the influences of various 3-D electrodes on epiretinal electrical stimulation. Non-planar electrodes had larger threshold currents than disk electrodes. Of the five types of electrodes, concave hemispherical electrodes may be the ideal option, considering their superior stimulation localization and electrode safety.
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Affiliation(s)
- Xun Cao
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Xiaohong Sui
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Qing Lyu
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Liming Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
| | - Xinyu Chai
- School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China.
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40
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Werginz P, Benav H, Zrenner E, Rattay F. Modeling the response of ON and OFF retinal bipolar cells during electric stimulation. Vision Res 2014; 111:170-81. [PMID: 25499837 PMCID: PMC4457536 DOI: 10.1016/j.visres.2014.12.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2014] [Revised: 11/11/2014] [Accepted: 12/02/2014] [Indexed: 11/15/2022]
Abstract
Retinal implants allowing blind people suffering from diseases like retinitis pigmentosa and macular degeneration to regain rudimentary vision are struggling with several obstacles. One of the main problems during external electric stimulation is the co-activation of the ON and OFF pathways which results in mutual impairment. In this study the response of ON and OFF cone retinal bipolar cells during extracellular electric stimulation from the subretinal space was examined. To gain deeper insight into the behavior of these cells sustained L-type and transient T-type calcium channels were integrated in the synaptic terminals of reconstructed 3D morphologies of ON and OFF cone bipolar cells. Intracellular calcium concentration in the synaptic regions of the model neurons was investigated as well since calcium influx is a crucial parameter for cell-to-cell activity between bipolar cells and retinal ganglion cells. It was shown that monophasic stimulation results in significant different calcium concentrations in the synaptic terminals of ON and OFF bipolar cells. Intracellular calcium increased to values up to fourfold higher in the OFF bipolar model neuron in comparison to the ON bipolar cell. Furthermore, geometric properties strongly influence the activation of bipolar cells. Monophasic, biphasic, single and repetitive pulses with similar lengths, amplitudes and polarities were applied to the two model neurons.
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Affiliation(s)
- P Werginz
- Institute for Analysis and Scientific Computing, Vienna University of Technology, 1040 Vienna, Austria
| | - H Benav
- Center for Ophthalmology, University of Tübingen, 72076 Tübingen, Germany
| | - E Zrenner
- Center for Ophthalmology, University of Tübingen, 72076 Tübingen, Germany; Center for Integrative Neurosciences, University of Tübingen, 72076 Tübingen, Germany
| | - F Rattay
- Institute for Analysis and Scientific Computing, Vienna University of Technology, 1040 Vienna, Austria.
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41
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Abramian M, Lovell NH, Morley JW, Suaning GJ, Dokos S. Activation and inhibition of retinal ganglion cells in response to epiretinal electrical stimulation: a computational modelling study. J Neural Eng 2014; 12:016002. [PMID: 25426958 DOI: 10.1088/1741-2560/12/1/016002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Retinal prosthetic devices aim to restore sight in visually impaired people by means of electrical stimulation of surviving retinal ganglion cells (RGCs). This modelling study aims to demonstrate that RGC inhibition caused by high-intensity cathodic pulses greatly influences their responses to epiretinal electrical stimulation and to investigate the impact of this inhibition on spatial activation profiles as well as their implications for retinal prosthetic device design. Another aim is to take advantage of this inhibition to reduce axonal activation in the nerve fibre layer. APPROACH A three-dimensional finite-element model of epiretinal electrical stimulation was utilized to obtain RGC activation and inhibition threshold profiles for a range of parameters. MAIN RESULTS RGC activation and inhibition thresholds were highly dependent on cell and stimulus parameters. Activation thresholds were 1.5, 3.4 and 11.3 μA for monopolar electrodes with 5, 20 and 50 μm radii, respectively. Inhibition to activation threshold ratios were mostly within the range 2-10. Inhibition significantly altered spatial patterns of RGC activation. With concentric electrodes and appropriately high levels of stimulus amplitudes, activation of passing axons was greatly reduced. SIGNIFICANCE RGC inhibition significantly impacts their spatial activation profiles, and therefore it most likely influences patterns of perceived phosphenes induced by retinal prosthetic devices. Thus this inhibition should be taken into account in future studies concerning retinal prosthesis development. It might be possible to utilize this inhibitory effect to bypass activation of passing axons and selectively stimulate RGCs near their somas and dendrites to achieve more localized phosphenes.
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Affiliation(s)
- Miganoosh Abramian
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia
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42
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Kameneva T, Zarelli D, Nešić D, Grayden DB, Burkitt AN, Meffin H. A comparison of open-loop and closed-loop stimulation strategies to control excitation of retinal ganglion cells. Biomed Signal Process Control 2014. [DOI: 10.1016/j.bspc.2014.07.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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43
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Werginz P, Fried SI, Rattay F. Influence of the sodium channel band on retinal ganglion cell excitation during electric stimulation--a modeling study. Neuroscience 2014; 266:162-77. [PMID: 24560986 PMCID: PMC4423397 DOI: 10.1016/j.neuroscience.2014.01.067] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Revised: 12/10/2013] [Accepted: 01/26/2014] [Indexed: 11/28/2022]
Abstract
Electric stimulation using retinal implants allows blind people to re-experience a rudimentary kind of vision. The elicited percepts or so called 'phosphenes' are highly inconstant and therefore do not restore vision properly. The better knowledge of how retinal neurons, especially retinal ganglion cells, respond to electric stimulation will help to develop more sophisticated stimulation strategies. Special anatomic and physiologic properties like a band of highly dense sodium channels in retinal ganglion cells may help to achieve a focal activation of target cells and as a result better restoration of vision. A portion of retinal ganglion cell axons, about 40μm from the soma and between 25 and 40μm in length, shows a specific biophysical property. Electrode locations close to a band of highly dense sodium channels which were identified immunochemically show lowest thresholds during electric stimulation. The (modeled) thresholds for this kind of structure result in lowest thresholds as well. The influence on the location where action potentials are generated within the axon is far reaching. When a stimulating electrode is positioned far outside the actual band region the site of spike initiation still remains within the sodium channel band. These findings suggest to further examine the key mechanisms of activation for retinal ganglion cells because focal activation without influencing passing axons of neurons located far away can improve the outcome of electric stimulation and therefore the development of retinal implants.
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Affiliation(s)
- P Werginz
- Institute for Analysis and Scientific Computing, Vienna University of Technology, 1040 Vienna, Austria
| | - S I Fried
- Department of Neurosurgery, Massachusetts General Hospital, 02114 Boston, USA
| | - F Rattay
- Institute for Analysis and Scientific Computing, Vienna University of Technology, 1040 Vienna, Austria.
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Abstract
Retinal prosthesis has been translated from the laboratory to the clinic over the past two decades. Currently, two devices have regulatory approval for the treatment of retinitis pigmentosa. These devices provide partial sight restoration and patients use this improved vision in their everyday lives. Improved mobility and object detection are some of the more notable findings from the clinical trials. However, significant vision restoration will require both better technology and improved understanding of the interaction between electrical stimulation and the retina. This paper reviews the recent clinical trials and highlights technology breakthroughs that will contribute to next generation of retinal prostheses.
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45
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Abramian M, Lovell NH, Habib A, Morley JW, Suaning GJ, Dokos S. Quasi-monopolar electrical stimulation of the retina: a computational modelling study. J Neural Eng 2014; 11:025002. [PMID: 24556561 DOI: 10.1088/1741-2560/11/2/025002] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE In this study we investigated the feasibility of quasi-monopolar (QMP) electrical stimulation for retinal implant devices, using a computational model of the retinal ganglion cell layer. APPROACH When used with hexagonally arrayed multiple electrodes, QMP stimulation is a hybrid of hexapolar and conventional monopolar stimulus modes. In hexapolar mode, each active electrode is surrounded by six guards which collectively return the stimulus current, whereas in monopolar mode the injected stimulus current is returned through a distant return electrode. The QMP paradigm, on the other hand, distributes the return current between the guard electrodes as well as the distant return. The electrodes tested were 25, 50 and 100 µm in diameter, with hexagonally arranged centre-to-centre spacing of either double or quadruple this diameter. MAIN RESULTS Simulation results indicated that electrode size had minimal effects on subretinal threshold currents, whilst electrode configuration and centre-to-centre spacing played major roles in determining thresholds and spatial activation patterns. Threshold charge densities for 50 and 100 µm electrodes were generally within the safe limit. SIGNIFICANCE We found that QMP stimulation offers greater advantages compared to monopolar and hexapolar stimulation, in that it combines the low thresholds of monopolar stimulation with the localized spatial activation achieved with hexapolar electrodes during parallel stimulation.
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Affiliation(s)
- Miganoosh Abramian
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Australia
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Joucla S, Glière A, Yvert B. Current approaches to model extracellular electrical neural microstimulation. Front Comput Neurosci 2014; 8:13. [PMID: 24600381 PMCID: PMC3928616 DOI: 10.3389/fncom.2014.00013] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Accepted: 01/30/2014] [Indexed: 11/13/2022] Open
Abstract
Nowadays, high-density microelectrode arrays provide unprecedented possibilities to precisely activate spatially well-controlled central nervous system (CNS) areas. However, this requires optimizing stimulating devices, which in turn requires a good understanding of the effects of microstimulation on cells and tissues. In this context, modeling approaches provide flexible ways to predict the outcome of electrical stimulation in terms of CNS activation. In this paper, we present state-of-the-art modeling methods with sufficient details to allow the reader to rapidly build numerical models of neuronal extracellular microstimulation. These include (1) the computation of the electrical potential field created by the stimulation in the tissue, and (2) the response of a target neuron to this field. Two main approaches are described: First we describe the classical hybrid approach that combines the finite element modeling of the potential field with the calculation of the neuron's response in a cable equation framework (compartmentalized neuron models). Then, we present a “whole finite element” approach allowing the simultaneous calculation of the extracellular and intracellular potentials, by representing the neuronal membrane with a thin-film approximation. This approach was previously introduced in the frame of neural recording, but has never been implemented to determine the effect of extracellular stimulation on the neural response at a sub-compartment level. Here, we show on an example that the latter modeling scheme can reveal important sub-compartment behavior of the neural membrane that cannot be resolved using the hybrid approach. The goal of this paper is also to describe in detail the practical implementation of these methods to allow the reader to easily build new models using standard software packages. These modeling paradigms, depending on the situation, should help build more efficient high-density neural prostheses for CNS rehabilitation.
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Affiliation(s)
- Sébastien Joucla
- Université de Bordeaux, Institut des Neurosciences Cognitives et Intégratives d'Aquitaine, UMR5287 Bordeaux, France ; CNRS, Institut des Neurosciences Cognitives et Intégratives d'Aquitaine, UMR5287 Bordeaux, France
| | | | - Blaise Yvert
- Université de Bordeaux, Institut des Neurosciences Cognitives et Intégratives d'Aquitaine, UMR5287 Bordeaux, France ; CNRS, Institut des Neurosciences Cognitives et Intégratives d'Aquitaine, UMR5287 Bordeaux, France ; Inserm, Clinatec, U1167 Grenoble, France ; CEA, LETI, Clinatec Grenoble, France
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Veraart C, Duret F, Brelén M, Oozeer M, Delbeke J. Vision rehabilitation in the case of blindness. Expert Rev Med Devices 2014; 1:139-53. [PMID: 16293017 DOI: 10.1586/17434440.1.1.139] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
This article examines the various vision rehabilitation procedures that are available for early and late blindness. Depending on the pathology involved, several vision rehabilitation procedures exist, or are in development. Visual aids are available for low vision individuals, as are sensory aids for blind persons. Most noninvasive sensory substitution prostheses as well as implanted visual prostheses in development are reviewed. Issues dealing with vision rehabilitation are also discussed, such as problems of biocompatibility, electrical safety, psychosocial aspects, and ethics. Basic studies devoted to vision rehabilitation such as simulation in mathematical models and simulation of artificial vision are also presented. Finally, the importance of accurate rehabilitation assessment is addressed, and tentative market figures are given.
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Affiliation(s)
- Claude Veraart
- Neural Rehabilitation Engineering Laboratory, Universite catholique de Louvain, 54 Avenue Hippocrate Box UCL-54.46, B-1200 Brussels, Belgium.
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Abstract
PURPOSE OF REVIEW Outer retinal degenerations such as retinitis pigmentosa can cause profound vision loss. Various treatment strategies are being pursued to potentially restore functional vision in these patients. RECENT FINDINGS Advances in retinal prostheses have restored some vision in patients previously blind from retinitis pigmentosa. Optogenetics is another area that shows promise for restoration of vision. Transcorneal electrostimulation shows some efficacy to treat these patients as well. SUMMARY We review recent advances in optogenetics, visual prosthesis and electrostimulation to treat outer retinal degenerations.
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Al Abed A, Lovell NH, Suaning GJ, Dokos S. A continuum neuronal tissue model based on a two-compartmental representation of cells. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2013:6543-6. [PMID: 24111241 DOI: 10.1109/embc.2013.6611054] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Although significant advances have been made in continuum modeling of cardiac and smooth muscle tissue, the progress in neuronal continuum modeling has been slower. In this paper, a continuum neuronal tissue model based on a two-compartmental representation of cells is presented. Each neuron is described using both a somatic compartment modeled by the classical Hodgkin-Huxley current kinetics and a dendritic compartment based on a passive RC formulation. In addition, a synaptic current is fed into the dendritic compartment to account for the presynaptic influence of cells located within the dendritic field of each soma. A number of cases are simulated, including intracellular current injection into either the dendritic or somatic compartments, as well as extracellular current stimulation with and without synaptic input into neurons. The model incorporates a number of parameters controlling neuronal excitability which can be adjusted to validate each neuron's responses against experimental data, allowing for the modeling of different neuronal cell types and behaviors.
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The Argus™ II retinal prosthesis: Factors affecting patient selection for implantation. Prog Retin Eye Res 2013; 36:1-23. [DOI: 10.1016/j.preteyeres.2013.01.002] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Revised: 12/20/2012] [Accepted: 01/04/2013] [Indexed: 01/20/2023]
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