No abstract

No abstract

BackgroundEpiretinal prosthesis is one device for the treatment of blindness, which target retinal ganglion cells (RGCs) by electrodes on retinal surface. The stimulating current of epiretinal prosthesis is an important factor that influences the safety threshold and visual perception. Stochastic resonance (SR) can be used to enhance the detection and transmission of subthreshold stimuli in neurons. Here, it was assumed that SR was a potential way to improve the performance of epiretinal prosthesis. The effect of noises on the response of RGCs to electrical stimulation and the energy of stimulating current was studied based on a RGC model.MethodsThe RGC was modeled as a multi-compartment model consisting of dendrites and its branches, soma and axon. To evoke SR, a subthreshold signal, a series of bipolar rectangular pulse sequences, plus stochastic biphasic pulse sequences as noises, were used as a stimulus to the model. The SR-type behavior in the model was characterized by a “power norm” measure. To decrease energy consumption of the stimulation waveform, the stochastic biphasic pulse sequences were only added to the cathode and anode phase of the subthreshold pulse and the noise parameters were optimized by using a genetic algorithm (GA).ResultsWhen certain intensity of noise is added to the subthreshold signal, RGC model can fire. With the noise’s RMS amplitudes increased, more spikes were elicited and the curve of power norm presents the inverted U-like graph. The larger pulse width of stochastic biphasic pulse sequences resulted in higher power norm. The energy consumption and charges of the single bipolar rectangular pulse without noise in threshold level are 468.18 pJ, 15.30 nC, and after adding optimized parameters’s noise to the subthreshold signal, they became 314.8174 pJ, 11.9281 nC and were reduced by 32.8 and 22.0%, respectively.ConclusionsThe SR exists in the RGC model and can enhance the representation of RGC model to the subthreshold signal. Adding the stochastic biphasic pulse sequences to the cathode and anode phase of the subthreshold signal helps to reduce stimulation threshold, energy consumption and charge of RGC stimulation. These may be helpful for improving the performance of epiretinal prosthesis.

No abstract

Extracellular electrical stimulation of optic nerve can evoke both excitatory and localized visual sensations. These nerve responses are a potential substrate for restoring some function of vision to blind or near-blind patients. Optic nerve stimulation is a developing therapeutical method to treat blind subjects who still have functional retinal ganglion cells. However, the small diameter of optic nerve presents a challenge to determine the optimal geometry and position of spiral cuff electrode for evoking these responses. In order to determine the optimal spiral cuff electrode structure, a finite element model of optic nerve and surrounding structures were generated to simulate extracellular electrical stimulation. During simulation, variety of electrode structures were applied, and thickness of cerebrospinal fluid (CSF) was considered. Numerical calculations were performed by means of finite element method in three dimensions. The stimulation results indicate that bipolar electrodes can excite nerve, but the stimulation of tripolar electrodes structure is more effective. The thickness of CSF influences the stimulation results.