The Study Of Electrical Nerve Stimulation Device On Visual Cortex Using Current Steering Technology

Visual cortex visual prosthesis is used to restore visual function for patients with blindness.It converts the image information of the outside world into multiple channel electrical stimulation pulses and stimulate patient’s visual cortex through the microelectrode array to generate phosphine.The resolution of the optical illusion directly affects the quality of the visual function reconstruction. Using the finite number of electrodes to achieve electrical stimulation mode with high resolution is one of the bottleneck of visual cortex visual prosthesis.Virtual channel technique provides the possibility,virtual channel also known as current steering,can selectively activate the specific location of nerve area between two electrodes by applying current stimulation synchronously on the two adjacent electrodes to achieve the effect of increasing the number of effective stimulus channels.so, visual cortex neural electrical stimulator based on the current steering is the important research content of visual cortex visual prosthesis.The paper designs a set of visual cortex neural electrical stimulator based on current steering on the basis of analyzing the research around the world of nerve electrical technology.The system adopts MSP430F149 as the master control chip,by configurating stimulation waveform generating circuit,amplitude modulation circuit,single polarity input and bipolar output voltage controlled constant current circuit,and using serial port to communicate with PC to complete the design of the whole system.The design of system is composed of hardware design and software design.In the design of hardware circuit,Power circuit supplies the power for every module,MSP430F149 controls stimulation waveform generating circuit,serial communication circuit and amplitude modulation circuit composed of programmable digital potentiometer,the single polarity input and bipolar output voltage controlled constant current circuit is used to convert the single polarity voltage signal generated by stimulation waveform generating circuit into bipolar current signal,and serial port communication circuit is used to implement the communication between MSP430F149 and PC.The software design of system includes the PLC program design and PC software design.PLC program is written by C language and the development environment is the IAR EW430, the main function of the program is to generate voltage waveform of which current steering factor,frequency,pulse width and intensity can change, intensity program to control the amplitude modulation circuit,and serial port communication to realize the communication between MSP430F149 and PC.The PC is designed by VB to control the stimulator,the PC interface contains four parameters,such as current steeing,frequency,pulse width and intensity.By test,MSP430F149 has a good communication with PC and can generate voltage waveform which meets the requirements,also,the output voltage waveform throught the voltage cotrolled constant current circuit has good voltage/current switching linear and constant current characteristic within a certain range of load.At the same time,the SD rats experiment was carried using the current steering visual cortex neural electrical stimulator, implanting two stimulating electrodes and multichannel recording electrodes into the visual cortex of SD rats and processing the recording data of neural response.Result show that visual cortex gives response to stimulation,and the current steering neural stimulator is feasible.