Characterizing the reduction of stimulation artifact noise in a tripolar nerve cuff electrode by application of a conductive shield layer

Parisa Sabetian, Bita Sadeghlo, Chengran Harvey Zhang, Paul B Yoo. 

Medical Engineering and Physics (2017)

Nerve cuff electrodes are designed to record activity from a bundle of axons and are able to create excellent nerve recordings, but they are limited by a high signal to noise ratio. This study uses a conductive shield layer (CSL) to reduce the noise contamination of nerve recordings. 

All experiments were non-survival and involved six Spraque Dawley rats anesthetized using isoflurane. The nerve cuff electrode was placed on the sciatic nerve. Simulated external noise was created by introducing a change in resistance with the nerve cuff electrode. The electrode imbalance ratio was increased to further increase the noise levels. The CSL was then added and simulations were conducted with it and without. Results showed that the simulated noise amplitude was significantly reduced by an average of 80% when the CSL was added. They then tested the electrical conductivity of the CSL to see if it had an effect on the magnitude of the noise. The electrode imbalance ratio was set at 10 and the conductivity of the CSL was increased. The results exhibited that the amplitude of the noise was reduced by about 85% when the conductivity of the CSL had values between 1E-1 S/m (siemens per meter) and 1E4 S/m. 

Changing the geometry of the CSL was also tested. When the length of the CSL was increased there was a significant noise reduction. When the CSL was 77% of the cuff, there was a noise reduction of about 34%. When the CSL was made to match the size of the cuff, the noise was reduced by 86%. When observing how the CSL reduced the noise, it was shown that the CSL causes a more uniform potential gradient over the cuff. The noise generated a large potential gradient along the nerve cuff (8.6 mV), but that was significantly reduced when the CSL was added (1.8 mV).

In conclusion, external electrical noise can cause errors in recorded neural activity when using nerve cuff electrodes. The conductive shield layer can offer a solution to the limitations of the cuff electrode and help to create a more accurate animal nerve recording. While we do not use a nerve cuff electrode in our lab, I am interesting in learning about the solutions to external noise reduction in nerve recordings. This past week I have begun to dig deeper into some abnormalities I came across within the nerve recordings and have been curious about the different methods of reduction.

Paul