Little is known about how the retina's response to electrical stimulation is modified by temperatures. In vitro experiments are often used to inform in vivo studies, hence it is important to understand what changes...
moreLittle is known about how the retina's response to electrical stimulation is modified by temperatures. In vitro experiments are often used to inform in vivo studies, hence it is important to understand what changes occur at physiological temperature. To investigate this, we recorded from eight RGCs in vitro at three temperatures; room temperature (24°C), 30°C and 34°C. Results show that response latencies and thresholds are reduced, bursting spike rates in response to stimulation increases, and the spiking becomes more consistently locked to the stimulus at higher temperatures.
There is a potential for improved efficacy of neural stimulation if stimulation levels can be modified dynamically based on the responses of neural tissue in real time. A neural model is developed that describes the response of neurons to...
moreThere is a potential for improved efficacy of neural stimulation if stimulation levels can be modified dynamically based on the responses of neural tissue in real time. A neural model is developed that describes the response of neurons to electrical stimulation and that is suitable for feedback control neuroprosthetic stimulation. Experimental data from NZ white rabbit retinae is used with a data-driven technique to model neural dynamics. The linear-nonlinear approach is adapted to incorporate spike history and to predict the neural response of ganglion cells to electrical stimulation. To validate the fitness of the model, the penalty term is calculated based on the time difference between each simulated spike and the closest spike in time in the experimentally recorded train. The proposed model is able to robustly predict experimentally observed spike trains.
This research takes a step towards discovering underlying ionic channel changes in the glaucomatous ganglion cells. Glaucoma is characterized by a gradual death of retinal ganglion cells. In this paper, we propose a hypothesis that the...
moreThis research takes a step towards discovering underlying ionic channel changes in the glaucomatous ganglion cells. Glaucoma is characterized by a gradual death of retinal ganglion cells. In this paper, we propose a hypothesis that the ionic channel concentrations change during the progression of glaucoma. We use computer simulation of a multi-compartment morphologically correct model of a mouse retinal ganglion cell to verify our hypothesis. Using published experimental data, we alter the morphology of healthy ganglion cells to replicate glaucomatous cells. Our results suggest that in glaucomatous cell, the sodium channel concentration decreases in the soma by 30% and by 60% in the dendrites, calcium channel concentration decreases by 10% in all compartments, and leak channel concentration increases by 40% in the soma and by 100% in the dendrites.
Retinal implants restore limited visual perception to blind implantees by electrical stimulation of surviving neurons. We consider the efficacy of two electrical stimulation parameters, frequency of stimulation and interphase gap between...
moreRetinal implants restore limited visual perception to blind implantees by electrical stimulation of surviving neurons. We consider the efficacy of two electrical stimulation parameters, frequency of stimulation and interphase gap between cathodic and anodic phases, on the required charge to reach a desired neuronal spike rate. Using a Hodgkin-Huxley model of a neuron, we find the most efficient means of achieving a desired spike rate for neurons by electrical stimulation is to use a stimulation frequency identical to the desired spike rate, as well as a long interphase gap.
ABSTRACT Electrical stimulation of the retina have been shown to restore rubimentary vision to people who lost thier photoreceptors due to degenerative eye diseases. Models of the electrophysiological properties of two classes of retinal...
moreABSTRACT Electrical stimulation of the retina have been shown to restore rubimentary vision to people who lost thier photoreceptors due to degenerative eye diseases. Models of the electrophysiological properties of two classes of retinal bipolar cells (RBCs) were constrained and validated using experimental data from the literature. The models were used to investigate the response of RBCs to sinusoidal electrical stimulation of varying frequencies. Modelling predicts that the class of RBCs with low-voltage activated Ca2+ current is more responsive to sinusoidal stimulation at lower frequencies (2-10Hz), than at higher frequency (100 Hz).
There are 16 morphologically defined classes of rats retinal ganglion cells (RGCs). Using computer simulation of a realistic anatomically correct A1 mouse RGC, we investigate the effect of the...
moreThere are 16 morphologically defined classes of rats retinal ganglion cells (RGCs). Using computer simulation of a realistic anatomically correct A1 mouse RGC, we investigate the effect of the cell's morphology on its impulse waveform, using the first-, and second-order time derivatives as well as the phase plot features. Using whole cell patch clamp recordings, we recorded the impulse waveform for each of the rat RGCs types. While we found some clear differences in many features of the impulse waveforms for A2 and B2 cells compared to other cell classes, many cell types did not show clear differences.
Retinal ganglion cells (RGCs) are the sole output neurons of the retina that carry information about a visual scene to the brain. By stimulating RGCs with electrical stimulation, it is possible to elicit a sensation of light for people...
moreRetinal ganglion cells (RGCs) are the sole output neurons of the retina that carry information about a visual scene to the brain. By stimulating RGCs with electrical stimulation, it is possible to elicit a sensation of light for people with macular degeneration or retinitis pigmentosa. To investigate the responses of RGCs to high frequency bi-phasic pulse train stimulation, we use previously constrained models of multi-compartment OFF RGCs. The morphologies of mouse RGCs are taken from the Chalupa set of the NeuroMorpho database. The cell models are divided into compartments representing the dendrites, soma and axon that vary between the cells. A total of 132 cells are simulated in the NEURON environment. Results show that the cell morphology plays an important role in the response characteristics of the cell to high frequency bi-phasic pulse train stimulation.
ABSTRACT In this paper we address the stabilization problem of the nonlinear feedback systems with quantized measurements in the presence of bounded disturbances. Building on an approach applied in [Liberzon, Nesic, 2004] to the linear...
moreABSTRACT In this paper we address the stabilization problem of the nonlinear feedback systems with quantized measurements in the presence of bounded disturbances. Building on an approach applied in [Liberzon, Nesic, 2004] to the linear time-invariant systems with quantized feedback, we extend the results of [Kameneva, Nesic, 2008] to the quantized control systems with nonlinear dynamics. Using the time-sampled scheme proposed in [Liberzon, Nesic, 2004] and later used in [Kameneva, Nesic, 2008], we show that the nonlinear gain h stability is achievable for the nonlinear systems with quantized feedback.
In patients who have lost their photoreceptors due to retinal degenerative diseases, it is possible to restore rudimentary vision by electrically stimulating surviving neurons. AII amacrine cells, which reside in the inner plexiform...
moreIn patients who have lost their photoreceptors due to retinal degenerative diseases, it is possible to restore rudimentary vision by electrically stimulating surviving neurons. AII amacrine cells, which reside in the inner plexiform layer, split the signal from rod bipolar cells into ON and OFF cone pathways. As a result, it is of interest to develop a computational model to aid in the understanding of how these cells respond to the electrical stimulation delivered by a prosthetic implant. The aim of this work is to develop and constrain parameters in a single-compartment model of an AII amacrine cell using data from whole-cell patch clamp recordings. This model will be used to explore responses of AII amacrine cells to electrical stimulation. Single-compartment Hodgkin-Huxley-type neural models are simulated in the NEURON environment. Simulations showed successful reproduction of the potassium currentvoltage relationship and some of the spiking properties observed in vitro.
It is possible to cause a sensation of light in patients who have lost photoreceptors due to degenerative eye diseases by targeting surviving neurons with electrical stimulation by means of visual prosthetic devices. All stimulation...
moreIt is possible to cause a sensation of light in patients who have lost photoreceptors due to degenerative eye diseases by targeting surviving neurons with electrical stimulation by means of visual prosthetic devices. All stimulation strategies in currently used visual prostheses are open-loop, that is, the stimulation parameters do not depend on the level of activation of neurons surrounding stimulating electrodes. In this paper, we investigate a closed-loop stimulation strategy using computer simulations of previously constrained models of ON and OFF retinal ganglion cells. Using a proportional-integral-type controller we show that it is possible to control activation level of both types of retinal ganglion cells. We also demonstrate that the controller tuned for a particular combination of synaptic currents continues to work during retina degeneration when excitatory currents are reduced by 20%.
The aim of this work was to investigate how retinal ganglion cells (RGCs) respond to repetitive electrical stimulation in degenerative retina. The response of modeled ON and OFF cells was examined to bi-phasic pulse train stimulation of...
moreThe aim of this work was to investigate how retinal ganglion cells (RGCs) respond to repetitive electrical stimulation in degenerative retina. The response of modeled ON and OFF cells was examined to bi-phasic pulse train stimulation of varying frequencies. Previously developed models of RGCs were extended to include an experimentally observable balance of excitatory and inhibitory currents in degenerative retina. The phenomena of fading and dark phosphenes with retinal implants were investigated. A hypothesis for a mechanism contributing to these phenomena was formulated.
A model of the electrophysiological properties of ON and OFF retinal ganglion cells (RGCs) was constrained and validated using experimental data from the literature. Our simulations support experimental findings that differences in the...
moreA model of the electrophysiological properties of ON and OFF retinal ganglion cells (RGCs) was constrained and validated using experimental data from the literature. Our simulations support experimental findings that differences in the magnitude of the T-type Ca(2+) current explain differences in the intrinsic electrophysiology of ON and OFF RGCs. The models are used to investigate the potential for differential stimulation of ON and OFF RGCs during neuroprosthetic stimulation with sinusoidal current. The model predicts that OFF cells fire preferential over ON cells in a frequency band around 10 Hz.