Monopolar vs. bipolar subretinal stimulation—An in vitro study

Gerhardt, Matthias; Groeger, Gillian; MacCarthy, Niall

doi:10.1016/j.jneumeth.2011.04.017

Cited by 22 publications

(21 citation statements)

References 37 publications

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“…One such configuration we assessed was the hexagonal return, first proposed by Lovell et al 39 Perceptual thresholds in our study with the hexagonal return were found to be on average 2.5 times higher than those using the monopolar return. In addition to being the first report of hexagonal stimulation in humans, this result is consistent with what has been seen in preclinical retinal implant studies, where between two times 19 and six times 40,41 higher thresholds for hexagonal stimulation compared to monopolar stimulation have been reported. Although our preclinical study showed that return configurations such as common ground and hexagonal produce a narrower spread of activation in the retina compared to monopolar stimulation, 19 the benefits of using such return configurations for retinal stimulation are at present unclear.…”

Section: Stimulus Parameter Influence On Thresholdssupporting

confidence: 90%

Factors Affecting Perceptual Thresholds in a Suprachoroidal Retinal Prosthesis

Shivdasani

Sinclair

Dimitrov

et al. 2014

Invest. Ophthalmol. Vis. Sci.

112

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With suprachoroidal stimulation, anodic-first pulses with a monopolar return are most efficacious. To enable high rates, an appropriate combination of pulse width and interphase gap must be chosen to ensure low thresholds and electrode voltages. Electrode-retina distance needs to be monitored carefully owing to its influence on thresholds. These results inform implantable stimulator specifications for a suprachoroidal retinal prosthesis. (ClinicalTrials.gov number, NCT01603576.).

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Section: Stimulus Parameter Influence On Thresholdssupporting

confidence: 90%

Factors Affecting Perceptual Thresholds in a Suprachoroidal Retinal Prosthesis

Shivdasani

Sinclair

Dimitrov

et al. 2014

Invest. Ophthalmol. Vis. Sci.

112

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“…Intracochlear electrodes often are in contact with fluid of relatively consistent impedance whereas the retinal electrodes are in contact with the choroid, which is comprised of a heterogeneous assortment of connective tissue and blood vessels. 54,55 However, this does indicate that FMP stimulation is not merely replicating HP stimulation. While this study does not detect any significant functional difference between the two modes, it is possible that there would be perceptual differences that we are unable to determine using our analysis method.…”

Section: Retinal and Cortical Selectivitymentioning

confidence: 90%

“…Current shunting via the highly conductive choroidal blood vessels also may contribute. 54,55 Higher thresholds may have consequences in a clinical scenario as higher charge levels are more likely to be damaging to the surrounding tissue. The fact that many channels did not reach a saturation of responses at the maximum safe charge injection limits also is concerning as the focusing methods may not be able to reach the same levels of brightness as MP stimulation.…”

Section: Cortical Thresholdsmentioning

confidence: 99%

Spatial Restriction of Neural Activation Using Focused Multipolar Stimulation With a Retinal Prosthesis

Spencer

Fallon

Thien

et al. 2016

Invest. Ophthalmol. Vis. Sci.

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Citation: Spencer TC, Fallon JB, Thien PC, Shivdasani MN. Spatial restriction of neural activation using focused multipolar stimulation with a retinal prosthesis. Invest Ophthalmol Vis Sci. 2016;57:3181-3191. DOI:10.1167/ iovs.16-19325 PURPOSE. The resolution provided by present state-of-the-art retinal prostheses is severely limiting for recipients, partly due to the broad spread of activation in the retina in response to monopolar (MP) electrical stimulation. Focused multipolar (FMP) stimulation has been shown to restrict neural activation in the cochlea compared to MP stimulation. We extended the FMP stimulation technique to a two-dimensional electrode array and compared its efficacy to MP and hexapolar (HP) stimulation in the retina.METHODS. Normally-sighted cats (n ¼ 6) were implanted with a suprachoroidal electrode array containing 42 electrodes. Multichannel multiunit spiking activity was recorded from the visual cortex in response to MP, HP, and FMP retinal stimulation.RESULTS. When inferring retinal spread using voltage recordings off the stimulating array, FMP stimulation showed significantly reduced voltages in regions surrounding the primary stimulating electrode. When measuring the retinal and cortical selectivity of neural responses, FMP and HP stimulation showed significantly higher selectivity compared to MP stimulation (separate 2-way ANOVAs, P < 0.05). However, the lowest cortical thresholds for each stimulating electrode were higher for FMP and HP compared to MP stimulation (1-way ANOVA, P < 0.001). No significant differences were observed between FMP and HP stimulation in any measures.CONCLUSIONS. Focused multipolar and HP stimulation using a two-dimensional array are promising techniques to reduce the spread of activation for a retinal prosthesis. Clinical application would be expected to result in smaller phosphenes; thus, reducing phosphene overlap between electrodes and increasing the resolution at the expense of higher thresholds for activation.

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“…4A). Second, we also note that the so-called loose patch clamp technique allows the measurement of action potentials of ganglion cells at a sealed membrane patch (Stett et al, 2000;Gerhardt et al, 2011). Even though the underlying mechanisms of these processes are very different, this further indicates that signaling at the membrane remains intact during pipette aspiration experiments.…”

Section: Response To Confined Amp Stimulimentioning

confidence: 92%

Signaling in chemotactic amoebae remains spatially confined to stimulated membrane regions

Gerhardt

Walz

Beta

2014

Journal of Cell Science

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Recent work has demonstrated that the receptor-mediated signaling system in chemotactic amoeboid cells shows typical properties of an excitable system. Here, we delivered spatially confined stimuli of the chemoattractant cAMP to the membrane of differentiated Dictyostelium discoideum cells to investigate whether localized receptor stimuli can induce the spreading of excitable waves in the G-protein-dependent signal transduction system. By imaging the spatiotemporal dynamics of fluorescent markers for phosphatidylinositol (3,4,5)-trisphosphate (PIP 3 ), PTEN and filamentous actin, we observed that the activity of the signaling pathway remained spatially confined to the stimulated membrane region. Neighboring parts of the membrane were not excited and no receptor-initiated spatial spreading of excitation waves was observed. To generate localized cAMP stimuli, either particles that carried covalently bound cAMP molecules on their surface were brought into contact with the cell or a patch of the cell membrane was aspirated into a glass micropipette to shield this patch against freely diffusing cAMP molecules in the surrounding medium. Additionally, the binding site of the cAMP receptor was probed with different surface-immobilized cAMP molecules, confirming results from earlier ligand-binding studies.

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Monopolar vs. bipolar subretinal stimulation—An in vitro study

Cited by 22 publications

References 37 publications

Factors Affecting Perceptual Thresholds in a Suprachoroidal Retinal Prosthesis

Factors Affecting Perceptual Thresholds in a Suprachoroidal Retinal Prosthesis

Spatial Restriction of Neural Activation Using Focused Multipolar Stimulation With a Retinal Prosthesis

Signaling in chemotactic amoebae remains spatially confined to stimulated membrane regions

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