Sub-threshold Pre-pulse for Retinal Prosthesis Resolution
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Solution Overview
Problem
Current retinal prostheses face challenges in achieving high spatial resolution due to the lower resolution of electrode arrays compared to a healthy retina and the inability to mimic natural eye movements, leading to reduced image stability and contrast perception in visually impaired individuals.
Innovation Solution
The method involves selectively stimulating smaller retinal ganglion cells using sub-threshold anodic pre-pulses and supra-threshold cathodic pulses to maintain high spatial resolution, while avoiding larger cells, and utilizing a retinal prosthesis with an electrode array attached to the epiretinal surface to simulate natural neural processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional supra-threshold stimulation is used to activate retinal neurons, then visual perception is achieved, but spatial resolution is reduced due to activation of larger cells and spread of stimulation
Solution Approach 1:
The patent applies sub-threshold anodic pre-pulses before supra-threshold cathodic pulses to selectively hyperpolarize larger retinal ganglion cells. This preliminary action creates a state where larger cells are less likely to fire action potentials in response to subsequent stimulation, while smaller cells remain unaffected and can still be activated by the supra-threshold pulse, thereby improving spatial resolution
Solution Approach 2:
The patent uses differential pulse polarity (anodic vs. cathodic) and timing (pre-pulse vs. main pulse) to create selective stimulation effects on different cell types. The anodic pre-pulse specifically targets larger cells with their larger membrane surface area, while the subsequent cathodic pulse selectively activates smaller cells that were not hyperpolarized, achieving local quality differentiation in neural activation
2Productivity
If electrode arrays are used for retinal stimulation, then visual prosthesis function is achieved, but resolution is lower compared to healthy retina due to electrode spacing and compression effects
Solution Approach 1:
The patent changes the temporal parameters of stimulation by introducing a two-phase pulse protocol: a sub-threshold anodic pre-pulse followed by a supra-threshold cathodic pulse. This parameter change allows selective modulation of neuronal excitability states, enabling higher effective resolution from the same electrode array by preferentially activating smaller cells with smaller receptive fields
Solution Approach 2:
By applying the anodic pre-pulse before the main cathodic stimulus, the system prepares the neural tissue in a specific state where larger cells are hyperpolarized and less responsive, while smaller cells maintain normal excitability. This preliminary action compensates for the inherent resolution limits of electrode arrays by creating selective vulnerability to the main stimulus
3Power
If larger retinal ganglion cells are stimulated, then stronger visual signals are produced, but spatial detail and fine contrast perception are lost
Solution Approach 1:
The patent applies an anodic pre-pulse that hyperpolarizes larger retinal ganglion cells, creating a preliminary anti-action that reduces their excitability. This prevents these large cells from generating strong action potentials in response to subsequent cathodic stimulation, thereby reducing the dominance of large-cell signals that would otherwise wash out fine spatial detail and contrast information
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the perception of fine details and maintains image contrast by selectively activating smaller cells, improving the resolution and stability of artificial vision provided by the prosthesis.
Implementation Method 1
sub-threshold anodic pre-pulses to hyperpolarize the membrane potential of a population of retinal ganglion cells
Implementation Method 2
subsequently stimulating the population of retinal ganglion cells with a supra-threshold cathodic pulse
Data Source
AI summary
In order to generate the smallest phosphenes possible, it is advantageous to selectively stimulate smaller cells. By hyperpolarizing the somas of the large cells selectively with sub-threshold anodic ‘pre-pulse’ stimuli (making them more difficult to stimulate) and then selectively depolarize the smaller cells one can selectively stimulate smaller cells. Alternatively, one can hyperpolarize the dendrites of the cells with larger dendritic fields by applying sub-threshold anodic currents on surrounding electrodes and then depolarizing the smaller cells in the center. Further, one can manipulate the phases of an individual biphasic wave to affect selective stimulation resulting in more focal responses. It is possible to increase resolution with the ‘pre-pulse’ described above. One can also effect resolution by modifying the pulse order of the cathodic and anodic phases. Further, one can isolate the effect of the phases by separating them in time (long inter-phase interval) or by making one of the phases long and low amplitude—always keeping equal total charge for the two phases. As an example, one can preferentially stimulate smaller ganglion cells by providing a longer sub-threshold anodic pulse balanced with a shorter supra-threshold cathodic pulse. Preferentially stimulating the smaller ganglion cells will allow stimulation of different brightness levels while maintaining high spatial resolution.