The Experts below are selected from a list of 13335 Experts worldwide ranked by ideXlab platform
Gregg J. Suaning - One of the best experts on this subject based on the ideXlab platform.
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Differential electrical responses in retinal ganglion cell subtypes: effects of synaptic blockade and Stimulating Electrode location.
Journal of neural engineering, 2018Co-Authors: Chih Yu Yang, David Tsai, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. LovellAbstract:OBJECTIVE Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. APPROACH Using whole-cell patch clamp, we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of Stimulating Electrode location on the differences in stimulation thresholds between ON and OFF RGCs. MAIN RESULTS With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154; p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 µA to 22.3 ± 2.1 µA) over those of OFF RGCs (from 13.2 ± 0.7 µA to 13.1 ± 1.1 µA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the Stimulating Electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. SIGNIFICANCE Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.
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high amplitude electrical stimulation can reduce elicited neuronal activity in visual prosthesis
Scientific Reports, 2017Co-Authors: Alejandro Barrigarivera, Chih Yu Yang, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. Lovell, Amr Al AbedAbstract:Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow Stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of visual prostheses. As the conveyance of representation of complex visual scenes may require neighbouring Electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high Stimulating conditions in visual prostheses: (1) in vivo, using a suprachoroidal prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory Stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing Stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the Stimulating Electrode) being inhibited at certain Stimulating amplitudes, whilst other groups (far from the Stimulating Electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.
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performance of laser fabricated Stimulating Electrode arrays for a retinal prosthesis in saline
International IEEE EMBS Conference on Neural Engineering, 2009Co-Authors: Christopher W D Dodds, Nigel H. Lovell, Yan T Wong, P J Byrnespreston, M Rendl, Gregg J. SuaningAbstract:MicroElectrode arrays for a Stimulating retinal prosthesis were fabricated from laser etched platinum (Pt) foil encased in silicone. A total of 12 arrays were fabricated to test performance in saline. Hexagonal arrangements (N=6) with multiple (6) return Electrodes, as well as paired Electrodes (N=6) with single returns were constructed. Electron microscopy of the Electrode's surfaces was performed. Cyclic voltammetry was performed on all Electrodes to measure the real surface area. The Electrodes were submerged in saline in an incubator and biphasic pulses of ±162 µA and ±280 µA for 400 µs were applied at a rate of 67.1 Hz for 12 weeks. Microscopy and cyclic voltammetry were repeated and changes to the Electrode's surfaces were observed both by visual inspection of the micrographs and analysis of the cyclic voltammetry curves. Extensive corrosion to those Electrodes subjected to the higher current suggests a charge injection limit of less than the original 350µC/cm2 estimate. Analysis of different corrosion levels between the hexagonal and paired arrangements show that a hexagonally arranged Electrode array, with multiple return Electrodes, allows a greater stimulation current to be used without reaching the charge injection limit of the Electrodes.
Nigel H. Lovell - One of the best experts on this subject based on the ideXlab platform.
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Differential electrical responses in retinal ganglion cell subtypes: effects of synaptic blockade and Stimulating Electrode location.
Journal of neural engineering, 2018Co-Authors: Chih Yu Yang, David Tsai, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. LovellAbstract:OBJECTIVE Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. APPROACH Using whole-cell patch clamp, we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of Stimulating Electrode location on the differences in stimulation thresholds between ON and OFF RGCs. MAIN RESULTS With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154; p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 µA to 22.3 ± 2.1 µA) over those of OFF RGCs (from 13.2 ± 0.7 µA to 13.1 ± 1.1 µA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the Stimulating Electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. SIGNIFICANCE Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.
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high amplitude electrical stimulation can reduce elicited neuronal activity in visual prosthesis
Scientific Reports, 2017Co-Authors: Alejandro Barrigarivera, Chih Yu Yang, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. Lovell, Amr Al AbedAbstract:Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow Stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of visual prostheses. As the conveyance of representation of complex visual scenes may require neighbouring Electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high Stimulating conditions in visual prostheses: (1) in vivo, using a suprachoroidal prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory Stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing Stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the Stimulating Electrode) being inhibited at certain Stimulating amplitudes, whilst other groups (far from the Stimulating Electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.
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performance of laser fabricated Stimulating Electrode arrays for a retinal prosthesis in saline
International IEEE EMBS Conference on Neural Engineering, 2009Co-Authors: Christopher W D Dodds, Nigel H. Lovell, Yan T Wong, P J Byrnespreston, M Rendl, Gregg J. SuaningAbstract:MicroElectrode arrays for a Stimulating retinal prosthesis were fabricated from laser etched platinum (Pt) foil encased in silicone. A total of 12 arrays were fabricated to test performance in saline. Hexagonal arrangements (N=6) with multiple (6) return Electrodes, as well as paired Electrodes (N=6) with single returns were constructed. Electron microscopy of the Electrode's surfaces was performed. Cyclic voltammetry was performed on all Electrodes to measure the real surface area. The Electrodes were submerged in saline in an incubator and biphasic pulses of ±162 µA and ±280 µA for 400 µs were applied at a rate of 67.1 Hz for 12 weeks. Microscopy and cyclic voltammetry were repeated and changes to the Electrode's surfaces were observed both by visual inspection of the micrographs and analysis of the cyclic voltammetry curves. Extensive corrosion to those Electrodes subjected to the higher current suggests a charge injection limit of less than the original 350µC/cm2 estimate. Analysis of different corrosion levels between the hexagonal and paired arrangements show that a hexagonally arranged Electrode array, with multiple return Electrodes, allows a greater stimulation current to be used without reaching the charge injection limit of the Electrodes.
John W. Morley - One of the best experts on this subject based on the ideXlab platform.
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Differential electrical responses in retinal ganglion cell subtypes: effects of synaptic blockade and Stimulating Electrode location.
Journal of neural engineering, 2018Co-Authors: Chih Yu Yang, David Tsai, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. LovellAbstract:OBJECTIVE Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. APPROACH Using whole-cell patch clamp, we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of Stimulating Electrode location on the differences in stimulation thresholds between ON and OFF RGCs. MAIN RESULTS With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154; p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 µA to 22.3 ± 2.1 µA) over those of OFF RGCs (from 13.2 ± 0.7 µA to 13.1 ± 1.1 µA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the Stimulating Electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. SIGNIFICANCE Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.
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high amplitude electrical stimulation can reduce elicited neuronal activity in visual prosthesis
Scientific Reports, 2017Co-Authors: Alejandro Barrigarivera, Chih Yu Yang, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. Lovell, Amr Al AbedAbstract:Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow Stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of visual prostheses. As the conveyance of representation of complex visual scenes may require neighbouring Electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high Stimulating conditions in visual prostheses: (1) in vivo, using a suprachoroidal prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory Stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing Stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the Stimulating Electrode) being inhibited at certain Stimulating amplitudes, whilst other groups (far from the Stimulating Electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.
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An in-vivo paradigm for the evaluation of Stimulating Electrodes for use with a visual prosthesis.
ANZ journal of surgery, 2004Co-Authors: Vivek Chowdhury, John W. Morley, Minas T. CoroneoAbstract:Background: Electrical stimulation of the visual cortex with surface Electrodes is able to elicit basic visual perceptions in blind patients. The development of a visual prosthesis for the blind will require an in-vivo model for the optimization of cortical neurostimulation with multiElectrode arrays. Methods: In anaesthetized cats a bilateral craniotomy was performed and the dura was removed to expose the cerebral cortex. A prototype Stimulating Electrode array was placed on a gyrus in one hemisphere, and the transcallosal evoked response (TER) to cortical stimulation by this Electrode array was recorded at a homologueous region in the contralateral hemisphere. Results: The Stimulating Electrode array elicited TER of short latency (6.9 ms) in the contralateral hemisphere. Bipolar stimulation of adjacent Electrodes on the array evoked similar TER regardless of the polarity of stimulation. Electrodes spread apart on the array caused higher amplitude TER than Electrodes placed close together. MultiElectrode stimulation evoked lower amplitude TER than bipolar stimulation. Conclusions: This transcallosal model of cortical neurostimulation is a useful method to evaluate Electrode arrays and stimulation techniques in the development of a visual prosthesis.
Chih Yu Yang - One of the best experts on this subject based on the ideXlab platform.
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Differential electrical responses in retinal ganglion cell subtypes: effects of synaptic blockade and Stimulating Electrode location.
Journal of neural engineering, 2018Co-Authors: Chih Yu Yang, David Tsai, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. LovellAbstract:OBJECTIVE Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. APPROACH Using whole-cell patch clamp, we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of Stimulating Electrode location on the differences in stimulation thresholds between ON and OFF RGCs. MAIN RESULTS With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154; p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 µA to 22.3 ± 2.1 µA) over those of OFF RGCs (from 13.2 ± 0.7 µA to 13.1 ± 1.1 µA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the Stimulating Electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. SIGNIFICANCE Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.
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high amplitude electrical stimulation can reduce elicited neuronal activity in visual prosthesis
Scientific Reports, 2017Co-Authors: Alejandro Barrigarivera, Chih Yu Yang, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. Lovell, Amr Al AbedAbstract:Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow Stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of visual prostheses. As the conveyance of representation of complex visual scenes may require neighbouring Electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high Stimulating conditions in visual prostheses: (1) in vivo, using a suprachoroidal prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory Stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing Stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the Stimulating Electrode) being inhibited at certain Stimulating amplitudes, whilst other groups (far from the Stimulating Electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.
Socrates Dokos - One of the best experts on this subject based on the ideXlab platform.
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Differential electrical responses in retinal ganglion cell subtypes: effects of synaptic blockade and Stimulating Electrode location.
Journal of neural engineering, 2018Co-Authors: Chih Yu Yang, David Tsai, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. LovellAbstract:OBJECTIVE Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. APPROACH Using whole-cell patch clamp, we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of Stimulating Electrode location on the differences in stimulation thresholds between ON and OFF RGCs. MAIN RESULTS With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154; p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 µA to 22.3 ± 2.1 µA) over those of OFF RGCs (from 13.2 ± 0.7 µA to 13.1 ± 1.1 µA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the Stimulating Electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. SIGNIFICANCE Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.
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high amplitude electrical stimulation can reduce elicited neuronal activity in visual prosthesis
Scientific Reports, 2017Co-Authors: Alejandro Barrigarivera, Chih Yu Yang, Tianruo Guo, Socrates Dokos, Gregg J. Suaning, John W. Morley, Nigel H. Lovell, Amr Al AbedAbstract:Retinal electrostimulation is promising a successful therapy to restore functional vision. However, a narrow Stimulating current range exists between retinal neuron excitation and inhibition which may lead to misperformance of visual prostheses. As the conveyance of representation of complex visual scenes may require neighbouring Electrodes to be activated simultaneously, electric field summation may contribute to reach this inhibitory threshold. This study used three approaches to assess the implications of relatively high Stimulating conditions in visual prostheses: (1) in vivo, using a suprachoroidal prosthesis implanted in a feline model, (2) in vitro through electrostimulation of murine retinal preparations, and (3) in silico by computing the response of a population of retinal ganglion cells. Inhibitory Stimulating conditions led to diminished cortical activity in the cat. Stimulus-response relationships showed non-monotonic profiles to increasing Stimulating current. This was observed in vitro and in silico as the combined response of groups of neurons (close to the Stimulating Electrode) being inhibited at certain Stimulating amplitudes, whilst other groups (far from the Stimulating Electrode) being recruited. These findings may explain the halo-like phosphene shapes reported in clinical trials and suggest that simultaneous stimulation in retinal prostheses is limited by the inhibitory threshold of the retinal ganglion cells.