The Design of Cochlea Vestibular Stimulator

Abstract：Cochlea scale vestibule dysfunction may cause many diseases such as dizziness. Vestibular prosthesis can be used to replace absent vestibular function and alleviate the suffering of patients. After the prosthesis was used by many patients, people found that it can also alleviate the pain caused by tinnitus.

Vestibular electrical stimulation is the core of vestibular prosthesis。The original method of vestibular electrical stimulation may cause signal interference between channels. To Solve this problem, we propose a new method which name is Continuous Alternately Sampling.

Introduction

In the 1980s, Kuk et al. proposed the possibility of electrical stimulation of tinnitus. As the number of patients with cochlear implants has increased, it has been found that another effect of electrically stimulating the cochlea to produce hearing is to suppress tinnitus by electrical stimulation. Many patients with deafness have tinnitus, and it is reported that 77% or more of tinnitus patients disappear or are significantly relieved after undergoing cochlear implantation.

The animal experiments published by Gong and Merfeld in 2000 showed that the implanted electrodes can be used to stimulate the vestibular nerves that innervate the horizontal semicircular canal, thereby transmitting horizontal rotation information to the nervous system. In normal guinea pigs, due to the vestibular eye movement, the eyeball will rotate with the angular velocity of the head rotation, as shown in the first curve of Figure 1. After the semicircular canal is blocked by surgery, the vestibular system can no longer feel the movement. The rotation of the part, so the eyeball no longer rotates, as shown in curve B. Curve C shows that if the artificial vestibular organ is activated, the vestibular eye movement will partially recover. The guinea pig eye follows The rotation of the artificial vestibular device is rotated, similar to the eye movement caused by the normal vestibular organ.

Researchers at Harvard Medical School have shown that information transmitted by artificial vestibular devices not only causes reflexive responses in animals, but can also be accepted and utilized by more advanced nerve centers. Experimental animals continue to use artificial vestibular devices for more than three months. The researchers found that the animal’s nervous system can gradually learn how to make better use of this unnatural artificial information. They also confirmed that long-term electrical stimulation did not damage the nerves.The vestibular ocular reflex produced by electrical stimulation does not completely coincide with the natural reflex, but when the animal wears the artificial vestibular device for a period of time, it will slowly adjust and gradually conform.

Phillips and Rubinstein of the University of Washington found that the information provided by electrical stimulation can reinforce the natural susceptibility of the stimulated semicircular canal. This finding suggests that artificial vestibular organs can also be used in patients with reduced vestibular function. Guyot et al. at the University of Geneva repeated the results of experiments conducted by researchers at Harvard Medical School on animals.

At present, there are many problems in the artificial vestibular devices, one of which is the mutual interference between the channels in the multi-channel device. CIS strategy has been successfully applied in cochlear implants, we improve the CIS and use dynamic compensation to overcome side-effects.

Methods

In order to solve the problems existing in the current multi-channel artificial vestibular device, we use the Continuous Interleaved Sampling (CIS) method which is successfully applied in the cochlear implant device. The core of this method is to use a constant stimulation pulse frequency, the pulse between each channel has a constant offset in time, and the pulses of each channel do not overlap each other, as shown in Figure 2. The amplitude of each stimulation pulse is controlled by the envelope of the input signal of the corresponding channel. Constant pulse frequencies are typically in 100 to 1000 Hz.

Materials

Vestibular prosthesis system structure includes Filter, A/D, D/A, modulation, generator of pulse signal. Analog signal converted into digital signal after passing the filter. digital signal will be processed by processor and then send to D/A to convert analog. Modulation will transform the pulse signal witch produce by signal generator to AM electrical stimulation signal. This system designed in Cypress PSoC witch can reduce the circuit scale. Figure 3 is the circuit diagram of the Vestibular prosthesis system.

Results

I have not finished this design yet, so I just simulated the performance of filter on computer, and Figure 4 is the simulated results.

As we can see in Figure 4, the frequency response curve has the lowest amplitude on 50Hz, the filter have good performance.

Conclusion and Discussion

The power we used in our daily life is 50Hz, so filtering 50Hz is the most important step in my design, it will affect the next level of circuit badly. It’s performance is good, but not excellent. I need to adjust parameters of the filter in the future, or I can also redesign the filter’s structure to improve the performance.

Acknowledgements

I would like to express my gratitude to all those who helped me during the designing of this system. My deepest gratitude goes first and foremost to Professor Wang, my supervisor, for his constant encouragement and guidance.

References

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