Recording Low-Noise Directionally Peripheral Nerve Activity with a Novel Nerve Cuff Electrode

Sabetian,Parisa  1  ;    Koh, Ryan  1, 2  ;   Zariffa, José  1, 2, 3  ;   Yoo, Paul  1, 3  

1.   Institute of Biomaterials and Biomedical Engineering, University of Toronto;    2.   Toronto Rehabilitation Institute (TRI) - University Health Network (UHN) ;    3.   Department of Electrical and Computer Engineering, University of Toronto  

Background and Objective: Advances in electrode technology have facilitated the development of neuroprostheses for restoring motor/sensory function in disabled individuals. Artificial sensors and their detection algorithms provide reliable performance in different functional electrical stimulation (FES) system. However, they present problems, such as the need for frequent calibration, subject encumbrance, and cosmetic unacceptability, due to sensor dimensions and appearance. Neural recordings can also provide useful information regarding specific sensory or motor function that can be applied to FES systems for persons with spinal cord injury or stroke patients. Among myriad neural interfaces, the cuff electrode is an attractive tool for communicating with the peripheral nervous system. The tripolar cuff electrode is the most common nerve cuff design; however, the physical symmetry of this configuration generates compound action potential (CAP) recordings that are identical regardless of whether the neural activity is afferent or efferent in nature. The goal of this study is to design a nerve cuff configuration able to achieve low-noise directionally-sensitive recording of peripheral nerve activity. 

Method: We investigated the feasibility of using a tetrapolar (4 electrode contacts) nerve cuff. The rational for this design was based on the use of two sets of tripolar electrode signals which are measured differentially in a bipolar configuration for differentiating recorded efferent/afferent neural activity. In this manner, we obtained two low-noise signals that are subtracted to yield a directionally-sensitive ENG. A finite element model was implemented (Comsol Multiphysics) to simulate 800 CAPs recorded by a tetrapolar nerve cuff electrodes for 3um, 5um, 10um and 20um fibers. A spatiotemporal template matching algorithm was applied to discriminate afferent and efferent activity.

Results: The afferent/efferent signal-to-noise ratio classification accuracy was 78.6 ± 24.9% across 4 different noise levels (e.g., 0 dB, -5 dB, -12 dB, and -20 dB) corresponding to each fiber’s signal. In vivo experiments in anesthetized rats confirmed that the CAPs from the sciatic nerve were recorded in response to potassium chloride (KCl) applied to the proximal and distal direction of bipolar cuff electrode with opposite polarity.

Conclusion: The preliminary computational results indicate that directional sensitivity can be achieved using tetrapolar cuff electrode. In addition, our preliminary experimental results introduced a novel animal model to record non-electrically evoked CAP in both afferent and efferent pathways using bipolar electrode. Future studies will be aimed at investigating the feasibility of using tetrapolar electrode to record ‘directionally-sensitive’ neural activity applying KCl.